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Anchor Manual 2010

The Guide to Anchoring

anchor manual 2010

No part of this book may be reproduced in any form, by print, copy or in any other way without

written permission of vryhof.

Vryhof, Stevin, Stevpris, Stevshark, Stevtensioner and Stevmanta are registered trade marks.

Vryhof reserves all intellectual and industrial property rights such as any and all of their patent,

trademark, design, manufacturing, reproduction, use and sales rights thereto and to any article

disclosed therein.

All information in this manual is subject to change without prior notice. Vryhof Anchors is not

liable and/or responsible in any way for the information provided in this manual.

First edition published 1984. Print run 7,500 copies.

Second edition published 1990. Print run 7,500 copies.

Reprint second edition. Print run 5,000 copies.

Third edition published 2000. Print run 2,500 copies.

Reprint third edition print run 1,500 copies.

Second reprint third edition print run 1,000 copies.

First print fourth edition published 2006 print run 1,000 copies.

Second print fourth edition print run 1,000 copies.

Third print fourth edition print run 1,000 copies.

Fourth print fourth edition print run 1,000 copies.

Vryh of Anchors BV

P.O. Box 109, 2900 AC Capelle a/d Yssel, The Neth er lands

www.vryhof.com vryhof@vryhof.com

Since the beginning of exploration of oil & gas offshore the art of anchoring

has taken a dramatic turn. Vryhof Anchors was one of the pioneers and

achieved holding powers up to 25 times an anchor's own weight.

Consequently the company soon emerged as market leader in anchor

design and manufacturing and with over 7500 units sold, its anchors are

the most applied offshore.

Vryhof understood that clients’ needs cannot be satisfied by supply of

standard hardware alone. With best-in-class sales services it shared technology

to create fit-for-purpose mooring systems; it initiated lease/purchase

concepts and introduced an alliance of leading mooring component manu-

facturers in order to more efficiently serve a changing offshore industry in

the 1990s.

Exploration in ever deeper waters and more remote locations has encour-

aged the development of more advanced mooring solutions. Consequently

Vryhof anchor holding powers now reach beyond 75x their weight. Once

again, the industry welcomes new ways of cooperation to include supply of

complete mooring systems and lease concepts.

This sets the stage for Vryhof, who under new private ownership and with

a presence in major offshore arena’s will continue to responsibly introduce

quality designs in pace with industry's requirements; to explore opportunities

to approach clients in an open, sincere, professional manner and take its

world class services well into a new era for the benefit and satisfaction of its

clients.

Company profile

Introduction

A stone and something that looked like a rope. For millennia this was the

typical anchor. Over the last 25 years of more recent history, vryhof has

brought the art to a more mature status. They have grown into a world

leader in engineering and manufacturing of mooring systems for all kinds

of floating structures. In doing so the company has secured numerous

anchor and ancillary equipment patents, and shared its experience with others.

The company understands that the needs of the industry can not be satisfied

by the supply of standard hard-ware only. Universal and tailored solutions

rooted in proven engineering should be based on long practical experience.

Vryhof has been and will be introducing new and original anchor designs

well into the 21st century. With their products, advice and this manual, it

shares this knowledge with those who are daily faced with complex mooring

situations.

This manual is intended as a means of reference for all who purchase, use,

maintain, repair or are in any way involved with anchors. Though written

from one anchor manufacturer’s standpoint, the information contained

herein is applicable to many types of anchors. Total objectivity is, of course,

impossible.

It is hoped this manual will contribute to the work and success of all who

work with anchors. They are the only fixed reference point for many of the

floating structures on the world’s often turbulent waters.

General

Mooring systems

Mooring systems have been around just as long as man has felt the need for

anchoring a vessel at sea. These systems were used, and are still used, on

ships and consisted of one or more lines connected to the bow or stern of

the ship. Generally the ships stayed moored for a short duration of time

(days).

When the exploration and production of oil and gas started offshore, a

need for more permanent mooring systems became apparent. Numerous

different mooring systems have been developed over the years, of which a

short selection is presented here.

Semi-submersible drilling rig - generally the semi-submersibles are

moored using an eight point mooring. Two mooring lines come together at

each of the columns of the semi-submersible.

CALM buoy - generally the buoy will be moored using four or more moor-

ing lines at equally spaced angles. The mooring lines generally have a cate-

nary shape. The vessel connects to the buoy with a single line and is free to

weathervane around the buoy.

SALM buoy - these types of buoys have a mooring that consists of a single

mooring line attached to an anchor point on the seabed, underneath the

buoy. The anchor point may be gravity based or piled.

Turret mooring - this type of mooring is generally used on FPSOs and FSOs

in more harsh environments. Multiple mooring lines are used, which come

together at the turntable built into the FPSO or FSO. The FPSO or FSO is able

to rotate around the turret to obtain an optimal orientation relative to the

prevailing weather conditions.



semi-sub mooring



typical turret mooring

fig. 1-01

catenary system

fig. 1-02

taut leg system

Spread mooring - generally used on FPSOs and FSOs in milder environ-

ments. The mooring lines are directly connected to the FPSO or FSO at both

the stern and bow of the vessel.

When oil and gas exploration and production was conducted in shallow to

deep water, the most common mooring line configuration was the catenary

mooring line consisting of chain or wire rope. For exploration and produc-

tion in deep to ultra-deep water, the weight of the mooring line starts to

become a limiting factor in the design of the floater. To over-

come this problem new solutions were developed consisting of synthetic

ropes in the mooring line (less weight) and/or a taut leg mooring system

(fig. 1-01 and fig. 1-02).

The major difference between a catenary mooring and a taut leg mooring

is that where the catenary mooring arrives at the seabed horizontally, the

taut leg mooring arrives at the seabed at an angle. This means that in a taut

leg mooring the anchor point has to be capable of resisting both horizontal

and vertical forces, while in a catenary mooring the anchor point is only sub-

jected to horizontal forces. In a catenary mooring, most of the restoring

forces are generated by the weight of the mooring line. In a taut leg

mooring, the restoring forces are generated by the elasticity of the mooring

line.

An advantage of a taut leg mooring over the catenary mooring is that the

footprint of the taut leg mooring is smaller than the footprint of the cate-

nary mooring, i.e. the mooring radius of the taut leg mooring will be small-

er than the mooring radius of a catenary mooring for a similar application.

Mooring systems 7

fig. 1-03

fig. 1-04

Mooring components

A typical mooring system can be divided in three different components, the

mooring line, the connectors and the anchor point.

Mooring line

Chain

The most common product used for mooring lines is chain which is available

in different diameters and grades. Two different designs of chain are used

frequently, studlink and studless chain. The studlink chain is most common-

ly used for moorings that have to be reset numerous times during their life-

time, for instance semi-submersibles, while studless link chain is often used

for permanent moorings (FPSOs, buoys, FSOs). A chain mooring line can be

terminated in either a common link or an end link (fig. 1-03).

Wire rope

When compared to chain, wire rope has a lower weight than chain, for the

same breaking load and a higher elasticity. Common wire ropes used in off-

shore mooring lines are six strand and spiral strand. The wire rope is termi-

nated with a socket (for instance open spelter, closed spelter, CR) for con-

nection to the other components in the mooring system. Generally wire

rope is more prone to damage and corrosion than chain (fig. 1-04).

Synthetic fibre rope

A recent development is the use of synthetic fibre ropes as mooring line.

Typical materials that can be used are polyester and high modulus polyeth-

ylene (Dyneema). The major advantage of synthetic fibre ropes is the light

weight of the material and the high elasticity. The synthetic fibre rope is

generally terminated with a special spool and shackle for connection to the

other components in the mooring system.

Mooring components

fig. 1-05

fig. 1-06

fig. 1-07

fig. 1-08

Connectors

Shackles

The shackle is a connector that is very common in the offshore industry. It

consists of a bow, which is closed by a pin. Many different types of shackles

are available, depending on the application. The shackle can be used in

both temporary and permanent moorings (fig. 1-05).

Connecting link kenter type

The connecting link kenter type is most commonly used for the connection

of two pieces of chain mooring line, where the terminations of the two

pieces have the same dimensions. The connecting link kenter type has the

same outside length as a chain link of the same diameter. Generally

connecting links kenter type are not used in permanent mooring

systems, as they have a shorter fatigue life than the chain (fig. 1-06).

Connecting link pear shaped

The pear shaped connecting link is similar to the connecting link kenter

type, except that it is used for the connection of two pieces of mooring line

with terminations that have different dimensions. Like the connecting link

kenter type, the pear shaped connecting links are not used in permanent

mooring systems (fig. 1-07).

Connecting link c type

Like the connecting link kenter type, the connecting link c type is used for

the connection of two pieces of mooring line with terminations that have

the same dimensions. The major difference between the kenter type and

the c type is the way that the connector is opened and closed. This connec-

tor is generally not used in permanent moorings (fig. 1-08).

Mooring components

Swivels

A swivel is used in a mooring system, generally of a temporary type, to

relieve the twist and torque that builds up in the mooring line. The swivel is

often placed a few links from the anchor point, although it can also be

placed between a section of chain and a section of wire rope. There are

many different types of swivels available, although a disadvantage of most

common swivels is that they may not function while under load, which is

caused by high friction inside the turning mechanism. A new development is

swivels that are capable of swivelling under load, due to special bearing sur-

faces inside the mechanism (fig. 1-09).

Anchoring point

Dead weight

The dead weight is probably the oldest anchor in existence. The holding

capacity is generated by the weight of the material used and partly by the

friction between the dead weight and the seabed. Common materials in use

today for dead weights are steel and concrete (fig. 1-10).

fig. 1-10



fig. 1-09



Mooring components

fig. 1-12



Drag embedment anchor

This is the most popular type of anchoring point available today. The drag

embedment anchor has been designed to penetrate into the seabed, either

partly of fully. The holding capacity of the drag embedment anchor is gen-

erated by the resistance of the soil in front of the anchor. The drag embed-

ment anchor is very well suited for resisting large horizontal loads, but not

for large vertical loads although there are some drag embedment anchors

available on the market today that can resist significant vertical loads

(fig. 1-11).

Pile

The pile is a hollow steel pipe that is installed into the seabed by means of a

piling hammer or vibrator. The holding capacity of the pile is generated by

the friction of the soil along the pile and lateral soil resist-ance. Generally

the pile has to be installed at great depth below seabed to obtain the

required holding capacity. The pile is capable of resisting both horizontal

and vertical loads (fig. 1-12).

fig. 1-11



Mooring components

Suction anchor

Like the pile, the suction anchor is a hollow steel pipe, although the diame-

ter of the pipe is much larger than that of the pile. The suction anchor is

forced into the seabed by means of a pump connected to the top of the

pipe, creating a pressure difference. When pressure inside the pipe is lower

than outside, the pipe is sucked into the seabed. After installation the pump

is removed. The holding capacity of the suction anchor is generated by the

friction of the soil along the suction anchor and lateral soil resistance. The

suction anchor is capable of withstanding both horizontal and vertical loads

(fig. 1-13).

Vertical load anchor

A new development is the vertical load anchor (VLA). The vertical load

anchor is installed like a conventional drag embedment anchor, but pene-

trates much deeper. When the anchor mode is changed from the installa-

tion mode to the vertical (normal) loading mode, the anchor can withstand

both horizontal and vertical loads (fig. 1-14).

fig. 1-13



fig. 1-14



History of drag embedment anchors

History traces the use of anchors to China as far back as 2,000 BC, though it is quite probable that they

were used prior to this. At that time the general tendency was to use large stones, baskets of stones,

bags of sand or even logs of wood loaded with lead which were then fastened to lines. It was this

weight as well as a certain degree of friction on the bottom which secured a vessel in position.

With the introduction of iron into anchor construction, teeth or flukes were built on the anchor,

allowing penetration into the seabed, thus offering additional stability. Yet these primitive

anchors were of poor construction and often broke under pressure. Curved arms were intro-

duced in 1813, and from 1852, the so-called ‘Admiralty Anchor’ was used for ships of the Royal

Navy. Another refinement in the 19th century was the elimination of the stock, the crosspiece at

the top of an anchor which ensured that the positioning of the anchor would allow the flukes to

penetrate the soil. A stockless anchor was invented in 1821 and became popular, primarily as a

result of the ease of handling and stowing, qualities still valued today.

A large number of anchor types has been designed and commercialised over the years. Some

have prospered, others not. The most recent designs are the results of vast experience and exten-

sive testing, and are far more efficient than their historical predecessors. A short overview of the

anchors in use today, is presented on the following pages.

History of embedment anchors 13

anchor shackle

shank

fluke

stabilisers

Based upon certain charateristics such as fluke area, shank, stabilisers, it is

possible to classify the various anchor types. To allow a rough comparison of

anchor type efficiency, an indication (*) is provided for a 10 t anchor as (HOLDING

CAPACITY = WEIGHT * EFFICIENCY).

Class A efficiency range *33 to 55

slender anchors with ultra-penetration.

Characteristics of anchor types

StevprisClass A

Stevshark

FFTS

Class B efficiency range *17 to 25

anchors with ‘elbowed’ shank, allowing for improved penetration.

Characteristics of anchor types

Bruce TS

Hook

Bruce SSClass B

Class C efficiency range *14 to 26

anchors with open crown hinge near the centre of gravity and relatively

short shank and stabilisers or built-in stabilisers.

Characteristics of anchor types

Stevfix

Stevmud

Flipper Delta

StevinClass C

Class D efficiency range *8 to 15

anchors with hinge and stabilisers at the rear and relatively long shanks and

stabilisers.

Characteristics of anchor types

LWT

Moorfast - Stato - Offdrill

Boss

DanforthClass D

Class E efficiency range *8 to 11

anchors with very short, thick stabilisers; hinge at the rear and a relatively

short, more or less square-shaped shank.

Characteristics of anchor types

Stokes

Snugstow

Weldhold

AC14Class E

Class F efficiency range *4 to 6

anchors with square shank, no stock stabilisers. The stabilising resistance is

built-in the crown.

Characteristics of anchor types

Beyers

Union

Spek

US Navy StocklessClass F

Class G efficiency range *<6

anchors with small fluke area and stabilisers at the front of the shank.

Characteristics of anchor types

Stock

Dredger

Mooring Anchor

Single Fluke StockClass G

History of vryhof anchor designs

A brief chronological summary of the types of anchors vryhof has designed

for use in the offshore and dredging industries:

•1972 - The Stevin anchor: The original design. The wing was not yet

enlarged. The anchor had a square shank. It is no longer manufac-

tured.

•1974 - The Hook anchor: originally designed for permanent moorings.

This design was surpassed in 1980 by the Stevpris design and is no

longer manufactured.

•1977 - The Stevin Mk3 anchor: is the improved version of the original

Stevin anchor. It was equipped with an enlarged crown and fluke

area and a streamlined shank for more efficient penetration. This

anchor is still manufactured and in use in offshore and dredging

activities. It has all classification societies approvals.

Stevin

Hook

Stevin Mk3

History of vryhof anchor designs

•1978 - The Stevfix anchor: this anchor was designed with special fluke

points for harder soils and a larger fluke area than the Stevin, but

has been surpassed by the Stevpris anchor. It is no longer manufac-

tured.

•1979 - The Stevmud anchor: the Stevmud is essentially the Stevin anchor

with a considerably enlarged fluke area. This anchor type was also

surpassed by the Stevpris anchor and is no longer manufactured.

•1980 - The introduction of the Stevpris and Stevshark anchors. The

Stevpris anchor is a deep penetrating anchor with a plough

shaped shank, surpassing the performance of all earlier designs in

the vryhof range, and incorporating the latest experience, research

and knowledge of the anchor designer. The Stevshark anchor is a

specially reinforced Stevpris anchor, equipped with a serrated

shank and cutter-teeth for better penetration in hard soils, such as

coral types or sandstone. The fluke points are specially reinforced

to withstand high point loads.

Stevmud

Stevpris

Stevfix

History of vryhof anchor designs

•1990 - The Stevpris Mk5 and Stevshark Mk5 were introduced. The

improved versions of the original Stevpris and Stevshark anchors.

Improvements have concentrated on two features: higher holding

capacity and easier handling.

•1996 - Introduction of the Stevmanta VLA (Vertical Load Anchor). Based

on industry demand for an anchor that could withstand vertical

loads, the Stevmanta VLA was developed. The Stevmanta VLA is a

new design in which a traditionally rigid shank has been replaced

by a system of wires connected to a plate. The anchor is designed to

accept vertical (or normal) loads and is installed as a

conventional drag embedment anchor with a horizontal load to

the mudline to obtain the deepest penetration possible. By chang-

ing the point of pulling at the anchor, vertical (or normal) loading

of the fluke is obtained thus mobilising the maximum possible soil

resistance. As a VLA is deeply embedded and always loaded in a

direction normal to the fluke, the load can be applied in any

direction. Consequently the anchor is ideal for taut-leg mooring

systems.

Stevshark Mk5

Stevmanta

Theory

Anchor design used to be based on practical experience of the anchor man-

ufacturer only. Nowadays, science has become a major factor in the design

process, complementing the experience of the anchor manufacturer. Based

on test results, both in the laboratory and in the field, a much better under-

standing of anchor behaviour has been achieved.

The performance of an anchor is influenced by many different parameters,

of which the following are only a few: fluke area and design, shank design,

soil conditions, load conditions, type of mooring line.

This chapter presents a short overview of how these parameters influence

the performance of the anchor. It is by no means complete, but it will give a

better understanding of how an optimal anchor design can be achieved. In

the last part of this chapter, a few relevant test results are presented.

Introduction 25

Anchor holding capacity 26

fig. 2-02

fig. 2-01

fig. 2-03

fig. 2-04

Criteria for anchor holding capacity

The holding capacity of an anchor is governed by the following parameters:

•The fluke area, which is limited by the strength of the anchor design.

•The penetration of the anchor. The penetration of the anchor is governed

by the soil type (deep penetration in very soft clay and shallow penetra-

tion in sand), the anchor type (design), the type of mooring line that is

used (chain or wire rope) and the applied load.

An increase in fluke area or an increase in the penetration depth of the

anchor results in a higher holding capacity.

In the following paragraphs, the influences on the anchor penetration are

further clarified.

Streamlining of the anchor

A streamlined anchor is very important for optimal penetration in the soil.

As can be seen in fig. 2-01 and fig. 2-02, an anchor which has protruding

parts will encounter much more soil resistance and consequently will not

penetrate as deep as a more streamlined anchor with the same fluke area.

Shank shape

A square shank, which is common for most older type single shank anchors,

will cause penetration resist-ance due to the fact that the soil can not pass

easily past the shank. A clod of soil will form underneath the shank, effec-

tively increasing the resistance of the soil (fig. 2-03). Bevelling the shank

allows deeper penetration.When the single shank is replaced by a twin

shank construction (for instance Stevpris, FFTS), usually two thin parallel

steel plates, the soil can more easily pass through and past the shank, and

consequently the twin shank anchor can penetrate deeper (fig. 2-04).

Mooring line

An anchor connected to a wire rope mooring line will penetrate deeper

than the same anchor connected to a chain mooring line (fig. 2-05 and fig.

2-06). This is caused by the higher lateral resistance (penetration resistance)

along the chain mooring line. This effect is noticeable in all soil conditions,

but especially in very soft clay where very deep penetration can be

obtained. The holding capacity of a chain mooring line, due to friction in

and on the seabed, is larger than the holding capacity of a wire rope moor-

ing line.

When an anchor reaches its ultimate holding capacity, i.e. it will not resist

any higher loads, at shallow penetration a wedge shaped piece of soil (in

front and above the anchor) will fail. The holding capacity of the anchor can

then be described as a combination of the following parameters (fig. 2-07

and fig. 2-08):

•The weight of the anchor (A).

•The weight of the soil in the failure wedge (B).

•The friction of the soil in the failure wedge along fracture lines (C).

•Friction between fluke surface and soil (fluke area) (D).

•The bearing capacity of shank and mooring line (E).

•The friction of the mooring line in and on the soil (E).

Anchor holding capacity 27

fig. 2-05

fig. 2-06

fig. 2-07

fig. 2-08

Criteria for good anchor design

Anchor parameters can be scaled from geometrically proportional anchors

using the scale rules in table A.

There are several attributes of an anchor which are crucial in assuring its

effective performance:

•The anchor must offer a high holding capacity; a result of the fluke area

and shank design in combination with penetration and soil type.

•The design of the anchor should be such that the anchor is capable of

being used successfully in practically all soil conditions encountered over

the world, ranging from very soft clay to sand, corals and calcarenites.

•The fluke/shank angle of the anchor should be easily adjustable, allowing

the anchor to be quickly deployed in different soil conditions.

•The design must be so conceived and produced that the high loads com-

mon in practice can be resisted and that the anchor can be easily handled,

installed, retrieved and stored.

•The penetration of an anchor depends upon its shape and design.

Obstructing parts on the anchor should be avoided as much as possible.

•The stability of an anchor encourages its penetration and, consequently,

its holding capacity. Efficient stabilisers are an integral part of a good

anchor design.

•The shank must permit passage of the soil.

•The surface area of an anchor fluke is limited by the required structural

strength of the anchor.

•The anchor design must have optimal mechanical strength to fulfil

requirements and stipulations of the classification societies.

•The anchor should be designed to ensure an optimum between structur-

al strength of the anchor and holding capacity.

•The anchor should be streamlined for low penetration resistance.

table A

Scale influence

Model Reality Related

to Weight

Length LnW 1/3

Fluke area An

2W 2/3

Weight Wn

Penetration PnW 1/3

Moment Mn

4W 4/3

Moment of iner tia In

4W 4/3

Section Modulus Sn

Bend ing stress M/S n4/n3=n W 1/3

Shear strength F/A n3/n2=n W 1/3

Aspects of soil in anchor design 29

Aspects of soil mechanics in anchor design

Until the nineteen seventies anchor design was largely an empirical process.

There was not much science involved, more use of experience. It is not easy,

for instance, to calculate the Ultimate Holding Capacity (UHC) of an anchor

from the commonly known soil mechanics formulas. The main problem is

the prediction of the volume of soil mobilised by the anchor. To a large

degree, it is this volume which determines the UHC. Detailed understanding

of soil characteristics and behaviour is essential in the anchor design

process and of increasing benefit in handling at sea. It is this understanding

which is the hallmark of a competent anchor designer and builder.

For anchor design and installation, the availability of good soil data is of

utmost importance as the soil is of great influence on anchor behaviour. The

following are influenced by the soil conditions encountered:

Anchor type - some anchors are more suited for soft soil conditions (soft

clay), while others are more suited for hard soils (sand and hard clays),

although there are a number of anchor types on the market that are suited

for most soil conditions encountered.

Holding capacity - in hard soil like sand and hard clay, the maximum

attainable ultimate holding capacity with a certain anchor type and size is

higher than the attainable ultimate holding capacity in very soft clay.

Penetration and drag - in very soft clay the anchor will penetrate deeper

than in harder soil like sand. As a consequence, the drag length of the

anchor will also be longer in very soft clay than in hard soil.

Retrieval forces - when an anchor is installed in very soft clay, the required

retrieval forces will be higher than in hard soil like sand. For example, in

very soft clay the required retrieval force of an anchor can be equal to 80%-

90% of the installation load while in hard soil (sand) the retrieval force

might only be 20%-30% of the installation load.

Soil classification 30 Undrained Shear Strength (kPa)

Consistency ASTM BS

of Clay D-2488 CP-2004

Very soft 0 - 13 0 - 20

Soft 13 - 25 20 - 40

Firm 25 - 50 40 - 75

Stiff 50 - 100 75 - 150

Very stiff 100 - 200 150 - 300

Hard 200 - 400 300 - 600

Very hard > 400 > 600

table B

Soil strength is generally expressed in terms of the shear strength parame-

ters of the soil. The soil type is classified mainly by grain size distribution.

Grain size Soil descrip tion

< - 2 µm Clay

2 - 6 µm Fine Silt

6 - 20 µm Medium Silt

20 - 60 µm Coarse Silt

60 - 200 µm Fine Sand

200 - 600 µm Medium Sand

0.6 - 2 mm Coarse Sand

2 - 6 mm Fine Gravel

6 - 20 mm Medium Gravel

20 - 60 mm Coarse Gravel

60 - 200 mm Cobbles

> - 200 mm Boulders

IIn general, the soil types encountered in anchor design are sand and clay

(Grain diameter from 0.1 µm to 2 mm). However, mooring locations consist-

ing of soils with grain sizes above 2 mm, such as gravel, cobbles, boulders,

rock and such, also occur. Clay type soils are generally characterised by the

undrained shear strength, the submerged unit weight, the water content

and the plasticity parameters. The consistency of clays is related to the

undrained shear strength. However, American (ASTM) and British (BS) stan-

dards do not use identical values (table B).

The undrained shear strength values Sucan be derived in the laboratory

from unconfined unconsolidated tests (UU).

Soil classification 31

On site the values can be estimated from the results of the Standard

Penetration Test (SPT) or Cone Penetrometer Test (CPT). An approximate

relation between shear strength and the test values are shown in table C.

The mechanical resistance of sandy soils is predominantly characterised by

the submerged unit weight and the angle of internal friction, ϕ. These

parameters are established in the laboratory. An approxim-ate correlation

between the angle ϕand the relative density of fine to medium sand is given

in table D. The undrained shear strength of clayey soil can also be estimated

based on manual tests.

•In soft clay the thumb will easily penetrate several inches, indicating an

undrained shear strength smaller than 25 kPa.

•In firm (medium) clay the thumb will penetrate several inches with mod-

erate effort, indicating an undrained shear strength between 25 kPa and

50 kPa.

•Stiff clay will be easily indented with the thumb but penetration will

require great effort, indicating an undrained shear strength between 50

kPa and 100 kPa.

•Very stiff clay is easily indented with the thumbnail, indicating an

undrained shear strength between 100 kPa and 200 kPa.

•Hard clay is indented with difficulty with the thumbnail, indicating an

undrained shear strength larger than 200 kPa.

The rock strength can generally be described by its compressive strength

(table E).

A classification system for soil based on the carbonate content and grain

size of the soil (Clark and Walker), is shown on the laste page of this chapter.

SuUU SPT CPT

kPa kPa N MPa

0 - 13 0 - 25 0 - 2 0.0 - 0.2

13 - 25 25 - 50 2 - 4 0.2 - 0.4

25 - 50 50 - 100 4 - 8 0.4 - 0.7

50 - 100 100 - 200 6 - 15 0.7 - 1.5

100 - 200 200 - 400 15 - 30 1.5 - 3.0

> 200 > 400 >-30 >3.0

table C

Descriptive Relative Angle SPT CPT

term Density ϕN MPa

Very loose < 0.15 < 30 0- 4 0 - 5

Loose 0.15 - 0.35 30 - 32 4 - 10 5 - 10

Medi um dense 0.35 - 0.65 32 - 35 10 - 30 10 - 15

Dense 0.65 - 0.85 35 - 38 30 - 50 15 - 20

Very dense > 0.85 > 38 > 50 > 20

Descriptive term Compressive

strength qu[MPa]

Very weak < 1.25

Weak 1.25 –5

Moderately weak 5–12.5

Moderately strong 12.5 – 50

Strong 50 – 100

Very strong 100 – 200

Extremely strong > 200

table D

table E

Fluke/shank angle

The penetration of an anchor into a certain soil type is greatly influenced by

the selected fluke/shank angle. For hinging anchor types (Stevin, Danforth

etc.) the fluke/shank angle is the angle between the anchor shackle, the

hinge and the fluke tip. The method for measuring the fluke/shank angle

for fixed shank anchors (Stevpris, FFTS, etc.) is not well defined. Often it is

the angle between the anchor shackle, the rear of the fluke and the fluke

tip, but not all anchor manufacturers use the same definition.

The recommended fluke/shank angles for different soil conditions are pre-

sented in table F.

Some modern anchors, like the Stevpris Mk5, have an additional intermedi-

ate fluke/shank angle of 41o, which can be used in intermediate or more

complex soil conditions. For instance at a location where the anchor has to

pass through a layer of soft clay before penetrating into a layer of sand.

If an anchor is used with an incorrect fluke/shank angle, it will negatively

influence performance. This is the case for all anchor types.

In hard soil, an anchor with a fluke/shank angle of 320will give the highest

holding power. If an anchor is used with the fluke/shank angle set at 500, the

anchor will fail to penetrate into the seabed and will begin to trip, fall aside

and slide along the seabed (Fig. 2-9 and 2-10).

fig. 2-09

fig. 2-10

Soil type Approximate

fluke/shank angle

Very soft clay 50˚

Medium clay 32˚

Hard clay and sand 32˚

table F

If an anchor is used in very soft clay (mud) with the fluke/shank angle set at

32o, the anchor will penetrate into the seabed, however the penetration

will be less than when a fluke/shank angle of 50ois used. Consequently the

holding capacity will be lower when the fluke/shank angle is set at 32o, and

the drag length longer (Fig. 2-11).

Fluke/shank angle 33

fig. 2-11



mud angle

sand angle

Because the fluke area of an anchor is of great influence on the holding

capacity, it can be useful to compare the fluke area of different anchor

types that are available on the market today. In general, it can be stated

that two anchors of the same weight but of different type (for instance a

Stevin anchor and a Stevpris Mk5 anchor), do not necessarily have the same

fluke area. Consequently, two anchors of the same weight but different

type, will have different holding capacities.

Some examples:

Fig. 2-12 shows a Stevpris Mk5 anchor and a Moorfast anchor, both of iden-

tical weight. It demonstrates that in spite of being the same weight, the

fluke areas differ substantially. The ultimate holding capacity of the Stevpris

Mk5 anchor is 4 to 8.5 times higher than that of the same weight Moorfast

anchor.

Fig. 2-13 illustrates the difference in fluke area of the Stevpris Mk5 anchor

in comparison with the Bruce FFTS Mk4 anchor, both of which have identi-

cal weight.

Fluke area 34

fig. 2-13



fig. 2-12



Strength of an anchor design 35

Anchors should be designed to withstand the loads applied on them in the

different loading situations. Typical loading situations and areas of special

attention for anchors are:

•During the proof loading of the anchors in the factory, after construction

has been completed. On basis of the proof load results, the classification

societies issue the approval certificate.

While embedded in the seabed

•Depending on the soil conditions, different loading situations can occur

on the anchor. In sands and clays, the load tends to be spread equally over

the anchor, which generally presents no problems. Retrieval is also very

simple, without excessive loads placed on the anchor.

•In very hard soils, the anchor has to be able to withstand the load with

only one or two of the fluke tips buried in the soil, as penetration in very

hard soil conditions is generally shallow.

•In very soft clays (mud) penetration of the anchor is uncomplicated.

However, recovery of the anchor can cause high loads, sometimes exceed-

ing the load that was used to install the anchor.

•Sidewards forces on the top of (shallow) buried anchors can be so

extreme that no anchor is capable of resisting them.

During anchor handling

•Care should be taken during the handling of the anchors, as the loads

exerted by the winches, vessels and chain can sometimes exceed the struc-

tural strength of the anchor and cause damage. Anchor designers

attempt to design the anchors for these high loads, however this is not

always possible due to variations in the magnitude of the loads during

handling operations.

Strength of an anchor design 36

•Large forces can be exerted on the anchor when high winch power is

used, the anchor is caught on the anchor rack or caught behind the stern

roller of the AHV.

•The use of an improper anchor/chaser combination. When a chaser is used

that is either too small or too large, the chaser could jam on the shank of

the anchor and cause damage.

The strength of the Stevpris anchor is now more closely examined in the

light of the remarks made before.

Strength of the shank

The prismatic shape of the Stevpris anchor not only ensures optimal pene-

tration of the soil but also guarantees maximum strength. Although the

Stevpris design also has limitations, it is one of the better designs to with-

stand sideward forces on the shank, a frequent occurrence in practice.

When using an anchor in very soft clay (mud), the bending moment on the

shank is low during the installation and when the anchor is in the soil.

However, during the breaking out of the anchor, high bending moments

could be introduced in the shank due to the high retrieval forces required

in very soft clay. In extremely sticky soils, the breaking out force of the

anchor can rise to 80% or 90% of applied anchor load; in certain instances,

it can even exceed 100%. To reduce these forces the breaking out proce-

dure is undertaken at low speed to allow time for the anchor to break out.

Strength of an anchor design 37

Strength of the fluke

The strength of the fluke and especially the fluke points of an anchor are

very important when working in extremely hard soils such as coral, lime-

stone and other rock types. It is possible in such instances that the total

holding capacity of the anchor will have to be sustained by the fluke points

alone. This means the structure must be strong enough to withstand

extreme bending forces. Loading in normal soil conditions is not a problem

due to the fact that the load is equally spread over the fluke.

In fig. 2-14, the different force points are shown for varying soil conditions.

The location on the fluke where the proofload is applied, is also indicated.

Strength in extremely hard soils

In very hard soils such as calcarenite, coral and limestone, an anchor will not

penetrate very deeply. Consequently the load applied to the anchor has to

be held by the fluke tips of the anchor and a small portion of the fluke. This

means that extremely high loads will be applied to the fluke tips, compared

to normal soil conditions such as sand and clay.

For use in very hard soil conditions, vryhof has designed the Stevshark

anchor, a modified version of the Stevpris anchor. To create the Stevshark,

the Stevpris anchor has been strengthened, consequently a Stevshark

anchor having the same outside dimensions and holding capacity as a

Stevpris anchor will be heavier.

Strength calculations of the Stevshark design have been made to guarantee

sufficient strength in the fluke points. The Stevshark anchor is designed to

withstand the application of the main part of the load on just its fluke tips.

fig. 2-14

rock

proofloadclay sand

Strength of an anchor design 38

To promote penetration, the Stevshark anchor has a serrated shank and can

be provided with cutter points on the fluke tips. Ballast weight can also be

added inside the hollow flukes of the anchor, up to 35% of the anchor

weight. This is important when working in very hard soil, where the anchor

weight pressing on the fluke tips promotes penetration, i.e. increased bear-

ing pressure.

The loads in a mooring system are caused by the wind, waves and current

acting on the floater. Depending on the location of the floater in the world,

different metocean conditions will prevail. In the table below, some

extreme metocean conditions are presented for different areas.

The loads induced in the mooring system can be divided into quasi-static

loads and total dynamic loads. The quasi static load is the load due to the

swell, wind, current and the frequency of the system. For quasi-static loads,

the systems tend to move at a low frequency, generally with a period of 140

to 200 seconds.

On top of this quasi-static load there are the individ-ual wave forces causing

a high frequency motion. The high frequency motion causes dynamic shock

loads with a period of 10 to 14 seconds due to the rolling of the vessel and

the movements of the anchor lines through the water. The quasi-static load

plus the individual wave forces is called the total dynamic load. Generally

the quasi-static loads will be equal to 50% to 90% of the total dynamic load.

See Fig. 2-15 for an example of the difference between the quasi-static load

and the total dynamic load.

Anchor loads and safety factors

fig. 2-15

4000

3000

2000

1000

8300 8400 8500 8600 8700 8800 9800

3895

Total dynamic

Quasi static

2342



Load in kN

Time in seconds

Location Waveheight Wave period Windspeed Current

msm/s m/s

Campos Basin 8 – 10 12 - 15 25 1

Gulf of Mexico 11 14 44 - 48 1

Northern North Sea 15 - 16 15 - 17 38 - 39 0.9– 1.2

Porcupine Basin 16 - 18 16 - 20 39 - 41 1.0 – 1.5

Vorine Basin 14 - 15 16 - 17 37 - 39 1.0 – 1.5

West of Africa 4 - 6 10 - 16 20 0.3 – 0.6

West of Shetlands 15 - 17 16 - 19 39 - 41 1.0 – 3.0

Anchor loads and safety factors

The quasi-static and total dynamic loads are generally calculated for the

intact and damaged load condition. The intact load condition is the condi-

tion in which all the mooring lines are intact. The damaged load condition

is the condition in which one of the mooring lines has broken.

From the quasi-static load and the total dynamic load, the required holding

capacity of the anchor can be calculated. This is called the ultimate holding

capacity (UHC) for drag embedment anchors and the ultimate pull-out

capacity (UPC) for VLAs. The required holding capacity is calculated by

applying the factors of safety specified by the classification societies.

In the tables G and H, the factors of safety are presented for the different

load conditions for drag embedment anchors (for instance the Stevpris Mk5

anchor), according to API RP 2SK. The factors of safety used by the major

classification societies are generally similar to those given in API RP 2SK (2nd

edition, 1996).

For VLAs, the recently used factors of safety suggested by ABS, are present-

ed in table I.

The factors of safety for VLAs are higher than the factors of safety required

for drag embedment anchors, due to the difference in failure mechanisms.

When a drag embedment anchor reaches its ultimate holding capacity, it

will continuously drag through the soil without generating additional hold-

ing capacity, i.e. the load will stay equal to the UHC. When a VLA exceeds its

ultimate pullout capacity, it will slowly be pulled out of the soil.

In table J the safety factors according to API RP 2SK for the mooring line are

presented for comparison purposes.

40 Permanent Quasi-static Total dynamic

mooring load load

Intact load condition 1.8 1.5

Damaged condition 1.2 1.0

Temporary Quasi-static Total dynamic

mooring load load

Intact load condition 1.0 0.8

Damaged condition Not required Not required

VLA Total dynamic

load

Intact load condition 2.0

Damaged condition 1.5

table G

table H

table I

Mooring line Quasi-static Dynamic

safety factors load load

Intact load condition 2.00 1.67

Damaged load condition 1.43 1.25

Transient load condition 1.18 1.05

table J

Drag embedment anchors

Drag embedment anchors are generally installed by applying a load equal to

the maximum intact load. For permanent mooring systems the installation

load should be held for the period specified by the classification societies

(see table K). The anchor will then have penetrated to a certain depth, but

will still be capable of further penetration because the ultimate holding

capacity has not been reached. The anchor will also have travelled a certain

horizontal distance, called the drag length. After installation the anchor is

capable of resisting loads equal to the installation load without further pen-

etration and drag. When the installation load is exceeded, the anchor will

continue to penetrate and drag until the soil is capable of providing suffi-

cient resistance or the ultimate holding capacity has been reached. However,

there are certain effects which allow the anchor to withstand forces larger

than the installation load without further penetration and drag. These are:

The set-up and consolidation effect

Set-up and consolidation mainly occur in clayey soils. The penetrating

anchor disturbs the soil and the soil temporarily loses strength. With time,

the disturbed clay reconsolidates to its initial shear strength, this takes from

a few hours up to 1 month, depending on the soil type. Because not all the

soil around the anchor is disturbed, the set-up effect factor is less than the

sensitivity index indicates. The disturbance mainly reduces the soil resis-

tance parallel to the fluke. On reloading, the parallel soil resistance gains

strength, it takes a larger load to move the anchor again. Equilibrium dic-

tates that also the normal load, i.e. the bearing soil resistance to the fluke,

increases; consequently the load at the shackle increases also with the set-

up factor. Observations on anchors for drilling rigs and theoretical consid-

erations for a 3 to 4 week consolidation time demonstrate a typical set-up

effect factor =1.5.

Anchor behaviour in the soil 41 Classification Required duration of

society maintaining tension

Lloyd’s Register of Shipping 20 minutes

American Bureau of Shipping 30 minutes

Det Norske Veritas (NMD) 15 minutes

table K

Anchor behaviour in the soil

The rate effect

An increased rate of loading increases the soil resistance, consequently the

anchor holding capacity increases. This must be taken into account with

respect to total dynamic loads. For anchor behaviour the rate effect factor

indicates how much higher the dynamic high frequency load may be with-

out causing extra movement of the anchor once installed at the installation

load. The rate of loading influences pore pressure variations, viscous inter-

granular forces and inertia forces. Typical rate effect factors are 1.1 to 1.3

for total dynamic loads, see Fig. 2-16 where the rate effect is presented for

two different soil conditions (Su = 10 kPa and Su = 50 kPa).

Using the rate effect and set-up factors, the behaviour of the anchor after

installation can be predicted more accurately.

Vertical Load Anchors

A VLA is installed just like a conventional drag embedment anchor. During

installation (pull-in mode) the load arrives at an angle of approximately 45

to 500to the fluke. After triggering the anchor to the normal load position,

the load always arrives perpendicular to the fluke. This change in load direc-

tion generates 2.5 to 3 times more holding capacity in relation to the instal-

lation load. This means that once the required UPC of the VLA is known, the

required installation load for the VLA is also known, being 33% to 40% of

the required UPC.

As a VLA is deeply embedded and always loaded in a direction normal to

the fluke, the load can be applied in any direction. Consequently the anchor

is ideal for taut-leg mooring systems, where generally the angle between

mooring line and seabed varies from 25 to 450.

fig. 2-16

1.2

1.1

0.9

0.8

0 200 400 600 800 1000

Time factor St

Rate effect factor

Su=10 kPa Su=50 kPa

Proof loads anchors

Proof loads for high holding power anchors

The proof load according to Classification Societies’ rules is applied at 1/3rd

of the fluke length and is carried out immediately on fabrication of the

anchor. It is obtained by placing the anchor in a test yoke in which a

hydraulic cylinder applies the test loads, controlled by a calibrated

manometer

(fig. 2-17). The vryhof anchor types have been approved by the following

Classification Societies:

•The American Bureau of Shipping

•Bureau Veritas

•Det Norske Veritas

•Germanischer Lloyd

•Lloyd’s Register of Shipping

•Registro Italiano Navale

•USSR Register of Shipping

•Nippon Kaiji Kyokai

•Norwegian Maritime Directorate

In the early days there were no specific regulations regarding the holding

power and strength of mooring anchors. The rules which did exist were

often followed regardless of the type of vessel.

Some anchors were approved as ‘high holding power’ anchors. This so-

called HHP approval was obtained after carrying out field tests in various

types of soil in which it had to be shown that an anchor provided a holding

power of at least twice that of a standard stockless anchor. If an HHP anchor

was requested by the owner, the anchor has proof tested in strict accor-

dance with the rules, nothing more. See table J for some examples of HHP

anchor proof loads. A more detailed overview of HHP anchor proof loads is

fig. 2-17



Anchor Proof Load Anchor

weight fac tor weight

1 t 26 t 26 x

5 t 79 t 15 x

7 t 99 t 14 x

10 t 119 t 12 x

15 t 155 t 10 x

20 t 187 t 9 x

table J

Proof loads anchors

given in the product data section.

The use of the specified proof loads for HHP anchors can lead to situations

where different types of anchors with the same holding capacity are proof

loaded at different loads, see fig. 2-18. From this figure it can be concluded

that the proof load of the anchors should preferably be related to the

break-load of the mooring line on the vessel.

Nowadays the rules and regulations are far more rigid, and the require-

ments have been substantially increased. There are now special rules for

‘mobile offshore units’ and ‘permanently moored structures’.

If anchors need mobile offshore units certification, the following properties

may be required:

•Proof load of the anchors at 50% of the breaking load of the chain.

•Submission of a strength calculation of the anchor to the classification

society prior to commencing anchor production: this includes determin-

ing the mechanical strength of the anchor as well as proving that the

applied material can withstand the proofload.

•A statement of documented holding power from the anchor supplier.

•Submittal of a Quality Assurance/Quality Control Manual.

In fig. 2-19, a mooring system is shown in which all of the components are

balanced. The strength of the mooring line, holding capacity of the anchor

and strength of the anchor are all in the correct proportion and comply with

the rules.

fig. 2-18

0 50 100 150 200 250

29 t Danforth

10 t Stevin Mk3

4.5 t Stevshark Mk5

4 t Stevpris Mk5

Proofload in t

Proofload HHP anchors, UHC=250 t.



fig. 2-19

0 10 20 30 40 50 60 70 80 90 100

Breakload chain

Ultimate holding

capacity anchor

Damaged load floater

Proofload chain

Pretension

load anchor

Intact load floater

Proofload anchor

Balanced mooring system API RP 2SK

Load in %

Quality control 45

The application of more advanced and complex technology in anchor

construction has brought about requirements for a systematic approach to

quality. Initiated by various authorities they are continuously refined and

followed up by operating companies such as vryhof anchor. Like other

companies, vryhof has become increasingly aware of the vital importance

of managerial aspects and their influence on the total quality-assurance

and control system.

Design and fabrication of anchors for permanent moorings are in

accordance with the quality requirements of the Rules NS/ISO 9001 as

described in our Quality Assurance Manual. Vryhof anchors obtained the

ISO 9001:2000 certificate No. 29389-2008-AQ-NLD-RvA Rev.1 issued by Det

Norske Veritas for ‘Design, Manufacture of anchors, and Sales of anchors

and mooring components’.

Quality control is maintained throughout production. A compilation of

certificates is presented to a client upon completion of a project.

Anchor tests

Introduction

In addition to prac ti cal expe ri ence of users and asso ciates, anchor tests are

one of the most reli able means of fore cast ing anchor per for mance and thus

mak ing a prop er choice of anchor type and size.

Examining anchor tests that have been car ried out in the past, cer tain

conclu sions can be made:

•Many tests were under tak en in which the results were record ed accu rate ly.

•Detailed reports, how ev er, have not been very com mon.

•Anchor tests of the past are not always easy to inter pret or com pare

because of dif fer ent soil and anchor types.

•Test results have not always been inter pret ed inde pen dent ly.

•The more tests results are strict ly com pared to prac ti cal results, the bet ter

one can fore cast the hold ing power and gen er al beha vi our in prac tice.

Vryhof is in the per fect sit u a tion of hav ing detailed test data avail able

togeth er with exten sive prac ti cal data obtained dur ing instal la tion and use

of anchors on pro jects on site.

Research into anchor beha vi our and the ulti mate hold ing capac ity of

anchors is often car ried out by test ing a model anchor, pref er ably fol lowed

by a full-scale test in the field. The opti mal anchor test con sists of model tests

with 10 kg anchors, fol lowed by full-scale tests with 1 t and 10 t anchors. The

anchors should be pulled until the ulti mate hold ing capac ity is reached.

It is obvi ous that full-scale test ing of anchors can be expen sive. Large AHVs,

strong winch es and strong moor ing lines are required, which are not always

avail able. For exam ple, a 5 t Stevpris Mk5 anchor, deployed in sand, is

capable of stop ping a mod ern AHV at its full bol lard pull.

Anchor tests 47

fig. 2-20 Drag

Holding Capacity

AGB

Testing a 10 t Stevpris Mk5 anchor to its ulti mate hold ing capac ity in sand

would require a hor i zon tal pull ing capac ity of approx i mate ly 600 t.

If anchor tests are to be com par able, the test ing pro gram should pref er ably

meet, as a min i mum, the fol low ing cri te ria:

•An accu rate and sophis ti cat ed meas ur ing system should be used.

•The anchors should be test ed up to their ulti mate hold ing capac ity.

•Drag and pen e tra tion of the anchor should be record ed dur ing test ing.

•The anchor should be held under ten sion with a blocked winch for 15

min utes, to inves ti gate any drop in hold ing capac ity.

Reading test curves

The beha vi our of an anchor dur ing ten sion ing can be accu rate ly inter pret ed

from the hold ing capac ity ver sus drag curve. Sample test curves are pre sent ed

in Fig. 2-20. Properly inter pret ed per for mance curves can explain a lot

about anchor beha vi our.

•Curve A is very steep and rep re sents a stream lined anchor in very stiff soil.

•Curve B is a nor mal curve for anchors in sand and medi um clay.

•Curve C is a curve of an unstable anchor. This can be caused by a wrong

fluke/shank angle set ting, a short stab i lis er or a fluke that is too long.

•Curve D is a nor mal curve for an anchor in very soft clay.

•Curve E is an anchor with a 32ofluke/shank angle in very soft clay.

•Curve F rep re sents an anchor that is turn ing con tin u ous ly. This can be

caused by the absence of stab il is ers, a too large fluke/shank angle or a

low effi cien cy anchor at con tin u ous drag.

•Curve G rep re sents an anchor pen e trat ing in a layer of stiff clay over lain

by very soft clay.

Anchor tests

Curves A, B, D, E and G show a very stable ris ing line, which indi cates that

the anchor builds up its hold ing capac ity con stant ly until the ulti mate hold ing

capac ity has been reached, after which the anchor shows con tin u ous drag.

The other curves are large ly self-explan a to ry.

Test results

Vryhof’s exten sive data base of test results with dif fer ent anchor types, sizes

and soil con di tions, has been fre quent ly used in anchor design. Data has

been obtained from prac tice, scale mod els and from third par ties. The data

has been inter pret ed and after wards incor po rat ed in the ulti mate hold ing

capac ity, drag and pen e tra tion graphs of the Stevin Mk3 and Stevpris Mk5

anchor as well as in the ulti mate pull-out capac ity graph of the Stevmanta VLA.

Norwegian Contractors (1984)

In 1984 Norwegian Contractors car ried out tests at Digernessundet, Stord,

Norway. The pur pose of these tests was to deter mine the cor rect anchor type

and size for the moor ing system of the Gullfaks A plat form dur ing the con struc -

tion of the plat form at Digernessundet. Although the con struc tion would took

place at one loca tion, it was known that three dif fer ent types of soil con di tions

would be encoun tered: sand, soft mud and an 8 m mud layer on rock. After the

initial trials the Stevpris anchor was select ed for fur ther test ing.

The 3 t Stevpris anchor that was used for the tests at a 3.30pull ing angle,

pro duced a max i mum hold ing capac ity of 150 t in the sand, 102 t in the very soft

clay and 150 t in the layer of mud on rock. As the moor ing system required

a sur vi val load of 1500 t, a 65 t Stevpris (mud loca tion), 40 t Stevpris (sand

loca tion) and 60 t Stevshark (mud on rock loca tion) were select ed for the final

moor ing. Fig. 2-21 shows the test results of the 3 t Stevpris anchor, while fig. 2-22

shows the result of the ten sion ing of the final anchors with a load of 820 t.

fig. 2-21

150

100

0 10 20 30 40

Sand 8 m soft clay 

on rock



Holding capacity in t

soft clay



Drag in meters

fig. 2-22

800

700

600

500

400

300

200

100

20 40 60 80

Full scale Gullfaks A anchors

Holding capacity in t

Drag in meters

A = 40 t Stevpris in sand

B = 60 t Stevshark in mud on rock

C = 65 t Stevpris in mud

Survival load = 1500 ton

* Final pretension load on site

Anchor tests 49

fig. 2-23

700

600

500

400

300

200

100

0 50 100 150 200 250 300 350 400 450 500

Drag distance in feet

7-2

7-3

7-4

7-1

2-2

2-1

Large scale anchor test jip - 7 & 2 t

Horizontal load in kips

Large scale anchor tests in the Gulf of Mexico

In 1990, tests were per formed with 2 t and 7 t Stevpris Mk5 anchors, as part

of an anchor test Joint Industry Project (JIP). The anchors were test ed using

a wire rope fore run ner.

The 2 t Stevpris anchor was test ed up to its ulti mate hold ing capac ity of 107 t

(235 kips). Due to insuf fi cient pull ing capac ity, the 7 t Stevpris anchor could not

be pulled up to its ulti mate hold ing capac ity. Based on the results of tests, the

ulti mate hold ing capac ity of the 7 t Stevpris anchor was cal cu lat ed to be larg er

than 338 t (745 kips) (fig. 2-23).

Anchor tests

Uplift

Stevpris anchors are well capable of resist ing uplift loads when they are deep -

ly embed ded. Anchors in sand and firm to hard clays do not pen e trate very

deeply and only take small uplift loads. Stevpris anchors installed in very soft

clay and mud pen e trate deeply, a typ i cal pen e tra tion for a 15 t anchor is 15 to

25 meters. Due to the inverse cat en ary in the soil, the anchor line arrives at the

anchor shack le at an angle of 20oto 30owith the mud line. Once the anchor is

installed, a load mak ing an angle up to 20owith the hor i zon tal at mud line will

not change the load ing direc tion at the anchor! A Stevpris anchor has been

test ed in the Gulf of Mexico with grad u al ly increas ing pull angle (fig. 2-24).

The max i mum resis tance was obtained for 18o uplift at mud line.

fig. 2-24



35 000

30 000

25 000

20 000

15 000

10 000

5 000

0 50 100 150 200 250 300

= dyn load

= pull angle

Line angle vs mudine

Line length pulled in feet

Line load in lbs

18˚

Cyclic effect fac tor

The load ing at the anchor is cyclic. Exxon per formed cyclic tests on anchors

report ed by Dunnavent and Kwan, 1993. Although the max i mum cyclic load

was less than the initial instal la tion load, the stat ic load applied after the

cycling phase revealed 25 to 50% larg er anchor resis tance than the initial

instal la tion load (fig. 2-25). This effect is explained by fur ther pen e tra tion

of the anchor. Applying this knowl edge to the anchors, the stat ic anchor

resis tance after some storm load ing improves by the cyclic effect fac tor of

1.25 to 1.5.

Anchor tests 51

fig. 2-25

0.15

0.1

0.0

0 50 100 150 200 250 300 350

Time in seconds

Anchor resistance in kN

Initial static capacity

Cycling

Increased capacity

vs initial static

Anchor tests 52

fig. 2-26

200

150

100

0 5 10 15 20 25 30 35



Line length pulled in feet

Block winch



Change mode



Line load in %



900 pulling 

angle with 

seabed in 

normal 

loading 

mode

Tests with Stevmanta anchors

Tests have been per formed in the Gulf of Mexico and offshore Brazil. The

Stevmanta anchor being pulled in with a load equal to F, accept ed a ver ti cal

load to the anchor of up to 2 times F! Amongst the many tests the anchor

relax a tion was meas ured. The anchor with a fluke area of 0.13 m2was

pulled in at 0opull angle (fig. 2-26), then load ed ver ti cal ly to a load equal to

1.6 times the max i mum instal la tion load. At this load the winch was

blocked.

Anchor tests 53

fig. 2-27

200

150

100

20.00 22.00 0.00 2.00 4.00 6.00 8.00

Time in hours

Line load in %



Change from 

pull-in to normal mode 



Block winch 



900 pulling 

angle with 

seabed in 

normal 

loading 

mode

This per mit ted the mon i tor ing of the load with time (fig. 2-27) as what

would be expect ed in real cir cum stanc es at a con stant load ed anchor line.

The results show that the hold ing capac ity of the anchor does not change

sig nif i cant ly dur ing con tin u ous load ing, as the observed decrease in ten sion

was due to move ment of the winch. The sub se quent pull ing at 7:00 AM

showed that for only a small move ment, the full plate capac ity (2 x instal la -

tion load) could be reached. Continuous pull ing caused the anchor to loose

resis tance and break out.

Anchor tests

To dem on strate that the fea ture of these anchors is not only a ver ti cal resis -

tance, the anchor was installed with a hor i zon tal pull, the mode changed to

the nor mal (ver ti cal) mode and the anchor sub se quent ly pulled with an

uplift angle of 30o(fig. 2-28). The beha vi our is sim i lar to the ear li er ver ti cal

pull test. However, for the 30opull angle the anchor did not break out but

moved slow ly along the pull ing direc tion through the soil. The graphs clear -

ly show this effect and that the anchor can be used for sub stan tial hor i zon -

tal loads.

fig. 2-28



200

150

100

0 5 10 15 20 25 30 35 40

Line length pulled in feet



Change from 

pull-in to normal mode 



Line load in %



300 pulling 

angle with 

seabed in 

normal 

loading 

mode

Soil table

Increasing lithification

Increasing grain size of

particulate deposits

0.002 mm 0.063 mm 2 mm 60 mm

Carbonate silt Carbonate sand Carbonate gravel

Carbonate clay Siliceous carbonate Siliceous carbonate

silt sand Mixed carbonate and

non-carbonate gravel

Calcareous clay Calcareous silica silt Calcareous silica sand

Clay Silica silt Silica sand Silica gravel

Calcilutite Calcisiltite (carb. Calcarenite (carb. Calcirudite (carb.

(carb. Calystone) Siltstone) Sandstone) Conglom. Or Breccia

Conglomeratic

Clayey calcilutute Siliceous calcisiltite Siliceous calcarenite calcirudite

Calcareous

Calcareaous claystone Calcareous siltstone Calcareous sandstone conglomerate

Conglomerate or

Claystone Siltstone Sandstone breccia

Fine-grained limestone Detrital limestone Conglomerat

limestone

Fine-grained Fine-grained siliceous Siliceous detrital Conglomerate

agrillaceous limestone limestone limestone limestone

Calcareous

Calcareous claystone Calcareous siltstone Calcareous sandstone conglomerate

Conglomerate of

Claystone Siltstone Sandstone Breccia

Crystalline limestone or marble

Conventional metamorphic nomenclature applies in this section

Approx. Rock Very weak Weak to moderately weak Moderately strong to strong Strong to extemely

strength strong

Cementation of Very weak to firmly Well cemented soil (well cemented)

soil cemented soil rock

Total carbonate content %

Practice

Although theoretical knowledge of anchors is essential for good anchor design

and selection, the practical issues are just as important. The handling of an

anchor and the selection and use of support equipment is of equal importance.

Anchor handling is a critically important and often complicated process. It is

influenced by such factors as the weight and shape of the anchor, the nature

of the soil, the depth of the water, the weather conditions, the available

handling equipment and the type and weight of mooring line. It is for these

reasons that anchor handling is a subject which requires careful considera-

tion. Without proper anchor handling, optimal performance of an anchor is

not possible.

In the process of handling anchors, various types of support equipment are

necessary or beneficial. An anchor manual would be incomplete without

consideration of these auxiliary items, the reasons for their use, their oper-

ation and the advantages and drawbacks involved.

This chapter gives an overview of the recommended procedures that should

be followed for anchor handling and the types and use of the support

equipment during the handling operations. The following handling

procedures are by no means complete, but they do give some suggestions

which can be applied to each anchor handling procedure and adapted for

specific circumstances and locations.

Some of the topics covered in this chapter are:

requirements for a soil survey, connection of the anchor to the mooring

line, chasers, handling the Stevpris anchor, handling the Stevmanta anchor,

the Stevtensioner, anchor handling/supply vessels.

Introduction 57

Soil survey 58

Typical contents survey report

• Cone pen e tra tion resis tance.

• Sleeve fric tion.

• Pore pres sure.

• SPT val ues.

• Gra nu lom e try and per cent age fines.

• Wet and dry den sities.

• Water con tent.

• Drained and undrained tri ax al tests.

• Undrained shear strength, also remould ed.

• Uncon fined com pres sion tests.

• Plas tic ity lim its.

• Spe cif ic grav ity.

• CaCO3con tent.

• Shell grad ing.

• Angu lar ity and poros ity.

• Com press ibil ity.

• Cemen ta tion.

• Nor mal ised rock hard ness test (point load test).

• RQD index, rock qual ity des ig na tion.

table K

For the dimen sion ing of drag embed ment anchors, the avail abil ity of site-spe -

cif ic soil data is impor tant. For advice on spec i fy ing drag embed ment anchor

type/size and cal cu lat ing expect ed beha vi our, the site-spe cif ic soil data should

be com pared with soil data of pre vi ous drag embed ment anchor (test) sites.

The soil sur vey require ment for the design of drag embed ment anchors usu al ly

con sists of only shal low bore holes, while in anchor pile design deep bore holes

are required. For suc tion anchor design therefore a more exten sive soil

inves ti ga tion is generally required when com pared to drag embed ment anchors.

When choos ing between anchor pile, suc tion anchor and drag embed ment

anchor the finan cial impli ca tions of the soil sur vey should be taken into account.

A typ i cal soil sur vey for drag embed ment anchor design requires a sur vey

depth of twice the length of the fluke in sand and 8 times the fluke length

in very soft clay. In most cases a depth of 8 to 10 meters is suf fi cient,

although in very soft clay a recon nais sance depth of 20 to 30 meters should

be con sid ered. For opti mal drag embed ment anchor dimen sion ing, each

anchor loca tion should ideal ly be sur veyed. The soil inves ti ga tion can con -

sist of bore holes, vib ro cores, cone pen e tra tion tests or a com bi na tion of

these. Cone pen e tra tion tests includ ing sleeve fric tion are pre ferred, but

they should be accom pa nied by at least one vib ro core or sam ple bore hole

per site to obtain a descrip tion of the soil. Depending upon the type of sur -

vey per formed and the soil con di tions encoun tered, the sur vey report

should present the test results obtained on site and in the labor a to ry includ -

ing the points as shown in table K.

It is pos sible to dimen sion the drag embed ment anchors based on lim it ed

soil infor ma tion (for instance fewer bore holes). The ‘lack’ of soil data can be

com pen sat ed by choos ing a con ser va tive (larger) anchor size.

Pile or anchor 59

The choice between piles and anchors is only pos sible for per ma nent

systems. Piles are not a good invest ment when an anchored entity must be

moved. But the choice is often made for piles on emo tion al grounds; a pile

does not drag! However, anchors that are prop er ly pre-ten sioned on site

will also not drag.

While it is a psy cho log i cal ly load ed sub ject, expe ri ence has shown that the

choice between anchor and pile is mere ly a mat ter of eco nom ics. The

required pile weight for a system is equal to the required weight of a

Stevpris anchor. Piles cost about 40% of equiv a lent capa bil ity anchors.

However, the instal la tion costs for piles are much high er. Piles require a fol -

low er and a pile ham mer. The instal la tion spread for piles is much more sig -

nif i cant; a crane barge with sup port spread ver sus the two anchor han dling

ves sels. The weath er downtime for a spread involv ing a crane ves sel is much

long er than when AHVs are used. To allow drag of the anchors dur ing pre -

ten sion ing, extra chain length is required. Sometimes the pre ten sion load

for piles is much less than for anchors. The sur vey work for anchors is gen er -

al ly much sim pler than for piles. When aban don ing a field, anchor remov al

is much cheap er than remov al of installed piles. The choice between piles

and anchors strong ly depends upon the cir cum stanc es. The table L can help

in esti mat ing the costs for the two alter na tives.

Suction piles are an alternative for drag embedment anchors and piles, also

for MODU applications. The advantage is the accurate positioning of the

suction piles. The disadvantage is the cost of the pile itself and the cost of

the installation.

Description Pile Suction Anchor

pile

Soil survey --+

Procurement +- -

Installation spread --+

Installation time --+

Pile hammer -++

Follower -++

Pump unit +- +

Pretensioning +- -

Extra chain ++ -

Rest value pile/anchor -++

Removal of anchor point -++

ROV +- +

+ less expensive - more expensive

table L

Mounting instructions

Stevpris / Stevshark Mk5

pin 1 pin 2

pin 3 pin 4

B1 B2



Forward fluke-shank connection

Remove the locking plates A1 and A2 which are tack-welded to the fluke

Aft fluke-shank connection

Move the pins 1 and 2 to the outer side. Remove the split pins and open

the locking plates B1 and B2. Move the pins 3 and 4 to the outside.

Plate 

A1 & A2

Pin 

1 & 2

Plate 

B1 & B2 Pin 

3 & 4

Fit the rear shank lugs into the fluke by means of a crane. Manoeuvre the

rear shank lugs with the notch into the gap in the flukes, as indicated in

the figures. When in position, rotate the shank forward to align the front

pins with the shank.

Attention

Make sure the serial number of the shank corresponds with the serial num-

ber of the fluke for reason of identification and certification.

Align pins 1 and 2 with the forward shank eyes. Move pins 1 and 2 back into

position. Place the shank in the sand, middle or mud position. Align pins 3

and 4 with the rear shank lugs. Move pins 3 and 4 back into position. Fit and

weld the locking

plates A1 and A2

on the fluke. See

welding detail

below. Close the

locking plates B1

and B2 and secure

with split pins.

Vryhof recommended welding procedure for locking plates A1 and A2

Fillet weld with electrode acc.AWS.E7018

Welding process SMAW electrode

welding position 2F

material S355J2G3 (St52-2N)

preheat material 50° C

interpass temp max 250° C

Mounting instructions

Stevpris / Stevshark Mk5



Serial number

Sand angle Middle angle Mud angle

Locking plate



Mud



Middle

Sand

Notch

Mounting instructions

Stevspris Mk6



pin 1 pin 2

pin 3 pin 4



Plate 

A1 & A2

Pin 

1 & 2

Forward fluke-shank connection

Remove the locking plates A1 and A2 which are tack-welded to the fluke.

Aft fluke-shank connection

Move the pins 1 and 2 to the inner side. Remove the splitpins and nuts

from pins 3 and 4 and move the pins 3 and 4 to the outside.



1234

Fit the rear shank lugs into the fluke by means of a crane. Manoeuvre the

rear shank lugs into the gap in the flukes, as indicated in the figures. When

in position, rotate the shank forward to align the front pins with the

shank.

Attention

Make sure the serial number of the shank corresponds with the serial num-

ber of the fluke for reason of identification and certification.

Align pins 1 and 2 with the forward shank eyes. Move pins 1 and 2 back into

position. Place the shank in the sand, middle or mud position. Align pins 3

and 4 with the rear shank lugs and insert them in the lugs. Tighten the bolts

and insert splitpins 3 and 4. Fit and weld the locking plates A1 and A2 on the

fluke. See welding detail below.

Vryhof recommended welding procedure for locking plates A1

and A2

Fillet weld with electrode acc.AWS.E7018

Welding process SMAW electrode

welding position 2F

material S355J2G3 (St52-2N)

preheat material 50° C

interpass temp max 250° C

Mounting instructions

Stevspris Mk6



Sand angle Middle angle Mud angle

Mud eye



Mid eye

Sand eye

Locking plate

Setting the fluke/shank angle

Introduction

In soil such as sand and medium to hard clay, an anchor with a fluke/shank

angle of 32owill give the highest holding power. An anchor with a 50o

fluke/shank angle in this soil will not penetrate but will drag along the

seabed. If used in mud a 50o fluke/shank angle is appropriate. An anchor with

a 32 ofluke/shank angle will penetrate less and generate lower holding

capacity in mud(fig. 3-01).

The Stevpris Mk5 anchor has an additional fluke/shank angle setting of 41o,

which can be adopted in certain layered soil conditions (table M).

Changing the fluke/shank angle on the Stevpris Mk3

This can be carried out within half an hour with the Stevpris anchor upside

down on deck.

Secure the anchor on deck. Connect a tugger wire (C) to the holes (D) on the

bottom side of the fluke. Change from mud to sand angle by removing the

locking plates and the two rear pins in (B), decrease the fluke/shank angle

by hauling the cable (C). Reinstall the pins and locking plates in (A). Seal

weld the lock-ing plates, do not weld them to the pins (fig. 3-02).

fig. 3-01

no penetration !

fluke angle too large in hard soil !

change from mud to sand angle

fig. 3-02

Soil type Optimal

fluke/shank

angle setting

Very soft clay (mud) 500

Certain layered soils 410*

Medium to hard clay

or sand 320

* Stevpris Mk5 only

table M

Setting the fluke/shank angle 65

Change from sand to the mud position, increase angle by veering (C), change

over pin and locking plates from (A) to (B). No special welding requirements

(fig. 3-03).

Changing the fluke/shank angle on the Stevpris Mk5 Changing the

fluke/shank angle on the Stevpris Mk5 anchor is even quicker. No welding

required. Veering and hauling (C) to change the fluke/shank angle as

above, the pin however remains in (A), the locking plate is secured by means

of a cotter pin (fig. 3-04).

change from sand to mud angle

fig. 3-03

change fluke/shank angle Stevpris Mk5

fig. 3-04

Connecting a swivel to the Stevpris anchor

To connect a swivel to the Stevpris anchor, several different configurations

are possible. These are:

Type I - The swivel is connected directly to the shank of the anchor thus

omitting the anchor shackle (fig. 3-05).

Jswivel shackle, Cend link, Benlarged link, Acommon link

Type II - The swivel is connected to the anchor shackle (fig. 3-06).

Jswivel shackle, Cend link, Benlarged link, Acommon link

Type III - The swivel is connected to the anchor shackle via a special design

end link

(fig. 3-07).

Kspecial end link, Jswivel, Cend link, Benlarged link, Acom-

mon link

Type IV - The swivel is part of a forerunner connected to the anchor shack-

le, for instance the forerunners VA02, VA04 and VA 06 described

in the product data section (fig. 3-08).

PL pear link, Acommon link, Benlarged link, Hswivel.

When a chaser is used in combination with the Stevpris and swivel, some of

the configurations mentioned above are more suitable than others. In gen-

eral, swivels are only designed to withstand longitudinal forces, and are

usually not designed for use in combination with chasers. The design of the

chaser tends to stop it at the swivel. Consequently, there will be high

bending forces on the swivel, which can result in damage or even breakage.

Connecting a swivel 66

J C B A

fig. 3-05

fig. 3-06

J C B A

fig. 3-07

K J C B A

fig. 3-08

PL A B H B A

Generally, it is best when the swivel is fitted some distance from the anchor

when a chaser is used. The chaser can then pass the swivel and stop on the

anchor shank. When a load is applied to the chaser, the swivel is only loaded

longitudinally. This means that in combination with the use of a chaser, the

configuration type III and type IV are preferred.

When the swivel (or swivel forerunner) is connected to the anchor shackle

by means of an end shackle and a chaser is used, the end shackle and the

anchor shackle should be connected bow through bow instead of pin

through bow as is normal practice. This to minimise the chance of damage

to the shackles.

The illustrations fig. 3-09 through fig. 3-14 show how and how not to

connect the swivel to the Stevpris anchor when using a chaser.

(See next page for fig. 3-13 and 3-14).

Connecting a swivel 67

damage possible!

fig. 3-09

NO !

fig. 3-10

damage possible!

fig. 3-11

fig. 3-12

NO !

Connecting a swivel

The best method for chasing with a swivel in the system is to maintain the

tension of the anchor line as much as possible during chasing. This will make

the chaser pass more easily over the swivel.

damage possible!

fig. 3-13

fig. 3-14

NO !

Chasers 69

Chasers and their application

To facilitate handling, pendant wires may be applied to retrieve the anchor.

These wires are connected to a pendant eye situated on the anchor and

equipped with a buoy for picking up. In deeper water higher anchor

break-out forces are encountered, resulting in longer, heavier pendant

wires and consequently larger buoys. Due to wear caused by the continuous

movement of the buoy by the waves, these pendants will break close to the

buoy. The buoys would then float free and the anchors are much more

difficult to recover.

To overcome this, chasers were introduced. These were rings ‘chased’ along

the cable towards the anchor and back again to a rig or handling vessel.

Their function was to ensure both installation and break-out of the anchor

without having to use a pendant line/buoy. The chaser system thus totally

eliminates buoys, partly eliminates cables and reduces wear on the system.

The cost of a chaser is small when compared to the cost of a mooring line. It

is therefore extremely important from an operator’s viewpoint that chasers

do not inflict damage to the mooring lines.

Chasers 70

Towing a chaser along mooring lines with, at times, high interface

pressures, must result in wear. It is thus essential that such wear is taken by

the chaser and not the mooring line. The chasers vryhof recommends are

manufactured in a material that is softer than the steel used for the

mooring line. Chaser wear is induced by the application of high interface

pressure between the mooring line and the chaser. High interface pressure

can arise from:

•Pulling the chaser along a slack mooring line.

•Maintaining high tension in the chaser workwire when chasing a

tensioned mooring line.

Chasing operations are best carried out on mooring lines which are fully

tensioned. There is little need for the application of high interface pressure

while chasing, the permanent chaser is captive on the mooring line and,

unlike the J-chaser, will not become disengaged due to a slack work wire.

For optimum chasing operations, the length of the chaser pendant line

should be at least 1.5 times the waterdepth.

There are many different types of chaser available on the market today.

A selection of the different chaser types is described in more detail on the

following pages.

Chaser types 71

fig. 3-16

fig. 3-15

The J-chaser

The J-chaser (fig. 3-15) is used on mooring lines where the anchor has to be

recovered and no permanent chaser has been installed, or the normal

recovery mechanism has failed. In other cases the J-chaser is used simply to

keep a chain free from a pipeline during deployment of the anchors. The

chaser is deployed over the stern roller of an AHV at approximately 1/3 of

the water depth. The chaser is towed across the mooring catenary until it

catches the chain. It is then towed into contact with the anchor shank/fluke

for anchor break-out and retrieval.

The permanent chain chaser

As a practical alternative to the buoy and pendant, the permanent chain

chaser (fig. 3-16) was introduced. Originally, simple shackles were used;

these were followed by special cast oval rings which were attached to a pen-

dant by a ‘bight’ of chain and shackle. Very soon afterwards the pear-shaped

chaser with shackle eye was introduced. The design of these chasers offers

superior sliding and penetration properties.

Chaser types 72

fig. 3-18

The detachable chain chaser

For rigs in service it is sometimes preferred to equip the mooring with a

chaser which does not require the anchor chain to be broken and re-made.

Detachable chain chasers (fig. 3-17) were introduced to satisfy this need.

The withdrawal and replacement of the single bolt permits easy assembly of

the chaser on the mooring cable.

The permanent wire chaser

The permanent wire chaser (fig. 3-18) was introduced when rigs moved to

deeper waters, and composite wire/chain mooring systems became neces-

sary. The chaser incorporates a ‘rocker’ which is centrally mounted on a

hinge bolt. The rocker has two opposing grooves, and when the chaser is

engaged with the mooring line, the wire slides through one of these

grooves irrespective of the angle which the chaser makes with the mooring.

The large radius at the base of the groove assists in reducing wear of the

rocker and avoids severe ‘opening’ of the lay of the wire if a loop of wire is

pulled during the handling process. The material of the rocker is not as hard

as the material of the wire. This means that wear is taken by the rocker

without damage to the wire and, because the rocker is easily removable,

replacement is relatively inexpensive. The permanent wire chaser is easily

detachable by removal and re-assembly of the hinge bolt and rocker.

Some designs of wire chaser incorporate fully rotating rollers over which

the mooring wire passes. To be effective such rollers need to be of a large

diameter and require to be supported by bearings. They are consequently

larger, heavier and much more costly than the permanent wire chasers dis-

cussed above, and because of their size, they require more power at the

AHV to penetrate the seabed and reach the anchor.

fig. 3-17

Chaser types 73

fig. 3-19

The J-lock chaser

The J-lock chaser (fig. 3-19) has been designed so that it can slide along the

chain in one direction and when the pulling direction is reversed, the chas-

er locks on the chain and does not slide any further. This means that the

tension in the mooring line can be wholly transferred from the rig to the

chaser. The J-shape permits catching the anchor chain after the anchor has

been installed. This means that this chaser can be used to assist in unforeseen

circumstances. The well-balanced and ‘guiding’ design of the chaser enables

catching the chain when the chaser approaches a mooring at a point where

the catenary angle is as high as 450.

When a normal permanent chaser is used under unforeseen conditions,

there is the chance that the AHV cannot break out the anchor by means of

the chaser. The J-lock chaser can help in such an instance. It is released from

a second AHV and slides along the chain towards the anchor. The design

prevents the J-lock chaser from sliding back. The J-lock chaser is stopped at

the permanent chaser. If the winch pull of both tugs is now increased, the

J-lock chaser prevents the permanent chaser from sliding away from the

anchor. Consequently, the forces required do not increase, and the anchor

can easily be broken out. After this operation, the J-lock chaser can be released

again.

This chaser can also be used when a very heavy chain has to be installed. It

assists during installation by lifting the chain.

Stevpris installation 74

fig. 3-20

chaser

fig. 3-21

always deck anchor with chain between flukes

fig. 3-22

quickly pass drum

fig. 3-23

triangular plates on drum

Stevpris deployment for MODUs

Introduction

Typical methods for deployment and retrieval of Stevpris anchors with an

anchor handling vessel (AHV) are described, focusing on the use of chasers

for handling the anchor (fig. 3-20). This is the most common practice on

mobile drilling rigs (MODUs). Handling using permanent pendant lines is

similar.

Deployment procedures for the Stevpris anchor will also be given for

permanent moorings where chasers are normally not used.

Laying anchors

It is preferred, and by some operators required, to deck the anchor before

run out to check the jewellery. Run the anchor line out the full distance with

anchor on deck or on roller, with the chain between the flukes (fig. 3-21).

Boat increases power until anchor line tension rises on rig winch tension

meter. When rig gives order to lower the anchor, veer pendant till anchor

arrives at roller. Allow the anchor some speed to negotiate the bump at the

change-over from the deck on to the roller (fig. 3-22).

If anchor is kept on roller, keep triangular plates below the main shackle on

the drum for stability of the anchor. Alternatively the chaser can be kept on

deck/roller. In this situation the propeller thrust passes underneath the

anchor and does not influence the fluke (fig. 3-23).

Stevpris installation 75

fig. 3-24

STOP !

fig. 3-25

fig. 3-26

wait for signal rig

Reduce propulsion momentarily when anchor passes the propeller thrust,

keep chaser on anchor head for control of anchor orientation and lower

anchor (fig. 3-24).

Once below the propeller wash zone, reactivate and maintain propeller

thrust to well above 30 tons. Keep constant tension in order to ensure

anchor does not fall through chaser, i.e. anchor remains in the chaser and

orientation of the anchor is correct (fig. 3-25).

Note: In some circumstances AHVs prefer to run the anchor hanging from

the pendant line below the propeller wash approximately 60 to 80 meter

above the seabed. This method requires less power on the winch during the

actual laying of the anchor. If this method is employed, make sure that at all

times the anchor is correctly oriented in the chaser. Keep constant tension

in the pendant line to prevent the anchor from falling through the chaser and

possibly turn.

Stop lowering when anchor hangs 10 to 15 meter above the bottom and

advise rig. Rig now instructs AHV to pay out until pendant line is 1.4 to 1.5

times the water depth in shallow water (100m) and 1.3 to 1.4 times in deep-

er water. AHV increases power till tension is again seen to rise at the rig, i.e.

the load in the line is larger than the chain-soil friction (fig. 3-26).

Rig commences to pull in slowly. AHV further increases power until tension

rises further at rig winch. At this moment rig orders AHV to lay the anchor.

AHV immediately stops the propulsion and is consequently pulled back-

wards. AHV pays out pendant and maintains paying out pendant after anchor

has landed on the bottom till a wire length of 1.5 to 2 times the water depth

is out. Enough slack wire must be paid out not to disturb the anchor during

buoying off or waiting. Stay above or behind the anchor.

Stevpris installation 76

fig. 3-30

patience in very soft soils !

fig. 3-27

rig hauls AHV slacks

fig. 3-28

do not pull after landing !

fig. 3-29

wrong ! keep cable 

under tension

Rig continues heaving the cable to a sufficient load, equal to the total

chain/soil friction plus 50 t to embed the anchor fully and create confidence

in good setting.

This also gives stability to the anchor when the AHV strips the chaser back

or buoys off the pendant. Now the AHV can retrieve the chaser and return

to the rig. If circumstances allow, the rig can tension up to the full preten-

sion load directly (fig. 3-27).

No extra pull after landing!

It is customary with older anchors such as Danforth, Moorfast, etc. to give

another pull once the anchor is on bottom. Do not do this with Stevpris

anchors. Once the anchor hits bottom, AHV should not pull again. Pendant

line must remain slack, otherwise anchor could land upside down!

(fig. 3-28). Suggestion: pre-load the anchors to the maximum required

pretension load as soon as the chaser is 100 meter or more ahead of the

anchor, i.e. do not wait. If anchor has not been laid correctly, a rerun can be

made immediately.

Retrieving anchors

The chaser should be brought to the anchor with a pendant of at least the

length of 1.5 to 2 times the water depth, measured from the stern roller.

Chaser should hang freely down from the anchor line till the bottom is

reached, i.e. slack in the pendant line. A too short pendant and/or too little

tension in the cable results in a situation as sketched (fig. 3-29).

While chasing, the rig should maintain tension of 60 to 70% of the pre-load

tension. No tension in pendant to ensure smooth passing over the chain.

When chaser is pulled into contact with anchor shank, increase thrust and

keep thrust while heaving, especially in rough water (fig. 3-30).

Stevpris installation 77

fig. 3-31

keep

pulling

rig

hauls

fig. 3-32

always deck anchor with chain between flukes

fig. 3-33

keep tension !

fig. 3-34

wrong ! anchor cannot deck !

The motion of the vessel itself now helps gradually to break the anchor

loose. Sequentially with the vessels motion the pendant is shortened

gradually. Anchors in very soft clay can be buried very deep. Have patience,

take your time and be gentle with the equipment; the anchor will come.

The rig can help and speed-up the operation by hauling the anchor line at

the same time! Once the anchor is off bottom, keep the chaser in contact

with the bow shackle by maintaining sufficient thrust (fig. 3-31).

Anchor orientation

The anchor flukes are always oriented towards the rig, on deck the anchor

lays on its back with shackle towards AHVs bow and cable between the

upwards directed fluke points. Check jewelry (fig. 3-32).

It is important to control the anchor orientation at all times for easy racking,

laying and decking of the anchor, i.e. keep pendant line under tension

while working the anchor. If the anchor slides through the chaser, the

anchor has to be pulled back to the stern roller and orientation checked

(fig. 3-33).

Decking the Stevpris anchor

If anchor is not correctly oriented, reduce propulsion and let anchor slide

down through the chaser. Rotation is easier while near the rig where all

loads are lower (fig. 3-34).

Stevpris installation 78

fig. 3-35 turn

fig. 3-36

fig. 3-37

stop / reduce 

propulsion

STOP !

Turn the anchor with a shot of propeller wash. Then pay out pendant, make

sure anchor is below the propeller wash away from the propeller influence

zone (fig. 3-35).

Increase propulsion moving AHV forward pulling chaser in contact with the

anchor. Make sure the stern roller is perpendicular to the chain, the chain

directing between the fluke points (fig. 3-36).

With sufficient bollard pull haul pendant, stop/reduce thrust for only a few

seconds when anchor passes the propeller wash onto the drum. Pull anchor

on the drum, allow the anchor to turn with its back on the roller, fluke

points up. Then pull further on deck (fig. 3-37).

Stevpris installation 79

With little tension in the line, the chain hangs steep against the fluke points

and anchor cannot rotate easily (A). Before rotating the anchor, pull on the

cable, the anchor will be free to turn (B) and (C) (fig. 3-38).

With anchor on the stern roller reactivate propulsion. For inspection anchor

can be pulled on deck. If required, change fluke angle to 32 degrees for

hard soil or to 50 degrees for very soft soil. Mind, every anchor type will be

unstable and drag in hard soil, stiff clay or sand with a fluke angle set for

mud! (fig. 3-39).

fig. 3-38

fig. 3-39

Stevpris installation 80

What not to do!

The anchor is approaching the drum. If the AHV maintains thrust, the water

flow will push the fluke (fig. 3-40).

If the propeller is not stopped, the thrust risks turning the anchor around

the cable then acting as a shaft (fig. 3-41).

The relative weight of the anchor increased by the thrust force on the fluke

will cause the anchor and the cable to slide down through the chaser and

control of anchor orientation is lost (fig. 3-42).

When the thrust is maintained while hauling in the chaser, the cable

prevents the anchor to turn on its back at the stern roller. Boarding will be

difficult now. The anchor could pass the stern roller on its side and get dam-

aged!

So stop/reduce the thrust just before the anchor passes the propeller wash

(fig. 3-43).

fig. 3-40

thrust on anchor makes it swing !

fig. 3-41

and rotate !

fig. 3-42

anchor slides through chaser

fig. 3-43

damage !

Stevpris installation 81

Racking the Stevpris

Rig heaves in anchor line, pulling AHV towards it. AHV keeps sufficient ten-

sion in pendant, chaser remains in tight contact with anchor, anchor

remains correctly oriented (fig. 3-44).

At some distance from the rig, AHV pays out winch wire while keeping suf-

ficient bollard pull (at least 1.5 times anchor weight) to keep chaser on

anchor head. Anchor flukes point towards the rig. Rig hauls, AHV veers

while keeping some tension in the pendant line transferring the anchor to

the bolster. The direction of the anchor cable must now be perpendicular to

the rack (fig. 3-45).

When anchor arrives at bolster, reduce tension to 15 tons. As soon as anchor

is resting on bolsters, slack pendant wire completely. If tension is not suffi-

cient, anchor falls out of control of the chaser and might rotate and make

racking difficult. If this occurs, bring anchor to the stern of the AHV, rotate

anchor with fluke points directing outwards and keep chaser tight on the

anchor (fig. 3-46).

Deploying Stevpris from the anchor rack

AHV receives pendant from rig and connects to AHV winch wire. AHV

moves to a position at a good distance but less than the water depth (for

instance 50 meter dependent on weather) from the rig. Stop winch and

keep sufficient tension, 20 to 30 tons or more as required to maintain the

chaser on the head of the anchor. Only now rig pays out cable while AHV

hauls in on the winch. The AHV maintains sufficient tension while pulling

the anchor to the stern roller. Reduce the power of the propeller as anchor

passes the wash zone and bring anchor on roller for inspection and reacti-

vate thrust (fig. 3-47).

fig. 3-44

keep tension !

fig. 3-45

keep tension !

fig. 3-46

wrong ! 

risk losing control 

over anchor orientation

fig. 3-47

keep tension !

Stevpris installation 82

Boarding the anchor in deep water

In deep water the weight of the anchor line becomes of predominant

importance. For line loads larger than 8 times the anchor weight the anchor

could be pulled against the chaser as illustrated, it could even position itself

upside down! In such cases boarding the anchor is difficult and damage

might occur (fig. 3-48).

The best and preferred solution is to pull the anchor from the bottom and

have the rig haul the anchor line, allowing the boarding of the anchor near

the rig where loads are smaller.

If this is not possible or allowed for some reason, another solution is to

reduce the weight that is hanging from the anchor. This can be done by

lifting the anchor line using a lock chaser or grapnel handled by a second

vessel (fig. 3-49).

It is recommended to board the anchor with the chain between the fluke.

The anchor fluke is generally designed to withstand loads up to 8 times the

anchor weight (fig. 3-50).

It happens that the anchor is accidentally pulled over the roller on its side.

Due to the large forces damage to shank and fluke might occur when the

chain is hanging over the anchor (fig. 3-51).

fig. 3-48

anchor weight

high tension

fig. 3-49

lock chaser

fig. 3-50

8 x anchor weight

fig. 3-51

large weight

Stevpris installation 83

fig. 3-52

fig. 3-53

with ballast in fluke use chain forerunner

chain

wire

If boarding the anchor on its side is inevitable, make sure that before

boarding, the vessel is turned to free the anchor line from the anchor and

haul gently. The chain will pass the stern roller next to the anchor. However,

this situation should be avoided as damage may occur (fig. 3-52).

Ballast in fluke

Using a wire rope forerunner and ballast material placed inside the hollow

fluke, the anchor may not topple over with the fluke points directed

downwards. A wire anchor line might be too light to position the anchor

correctly and the anchor may not topple over, the anchor could skid over

the seabed and prevent penetration.

When the fluke is ballasted, the weight of a chain forerunner will cause the

shackle to nose down and bring the fluke in penetration position (fig. 3-53).

Stevpris installation 84

Chaser equilibrium

To control the anchor, the chaser collar must always be on the anchor head.

The tension in the anchor cable must be equal or larger than 1.5 times the

weight of the anchor. If not, the anchor slides through the chaser and the

orientation is not controlled (fig. 3-54).

Equilibrium forces determine if chaser is in contact with the anchor. Near

bottom, the vertical load at the chaser from the anchor line Flv is small.

The chaser remains only in contact with the anchor if the bollard pull Fphis

larger than the horizontal line load Flhwhich in turn must be larger than

the anchor weight W (if not the anchor will slide down). The angle of the

pendant line must be larger than 45° (fig. 3-55).

Recommendation: Bollard pull must always be equal or larger than the line

tension, i.e. use a minimum bollard pull of 20 to 30 tons for a 12 to 15 ton

anchor. Use a minimum pendant line length of 1.4 to 1.5 times the water

depth in shallow water (100m) and 1.3 to 1.4 times the depth in deeper

water (fig. 3-56).

fig. 3-54

pendant line force

anchor line tension

anchor weight

fig. 3-55

Fpv

Flh

FlFlv

fig. 3-56

chaser

Deployment for permanent moorings

The simplest deployment procedure for the Stevpris anchor is to lower the

anchor to the seabed using the mooring line. When the anchor is nearly on

the seabed, the AHV should start moving slowly forward to ensure that the

anchor lands correctly on the seabed (fig. 3-57).

Another option for the deployment of the Stevpris anchor is to connect a

temporary installation bridle (wire rope) to the anchor. The bridle is

connected to the padeyes situated at the back of the shank of the anchor.

The AHV then lowers the anchor overboard while paying out the mooring

line and the bridle simultaneously (fig. 3-58).

To recover a Stevpris anchor after it has been installed, the AHV should take

the mooring line and pull it in the opposite direction that the anchor was

installed in, generally away from the centre of the mooring. The AHV

should recover the mooring line till a length of approximately 1.5 times the

water depth is still overboard.

When only 1.5 times the water depth of mooring line is left overboard, the

AHV should block the winch and keep a constant tension on the mooring

line equal to the pre-load tension. Once the anchor starts to move in the

soil, a lower tension in the mooring line can be used (fig. 3-59).

Stevpris installation 85

fig. 3-57

fig. 3-58

mooring line

temporary bridle

fig. 3-59

Piggy-backing

Introduction

Piggy-back is the practice of using two or more anchors in order to obtain

holding power greater than can be achieved with one only. Piggy-backing

is used when anchors are employed with insufficient holding capacity.

This can be caused by improper design for the particular environment or

insufficient anchor size.

In some soil conditions, the use of two smaller anchors in piggy-back can

offer an advantage over the use of one larger anchor. This can be the case

when the anchor has to hold in a certain layer and holding capacity in the

underlying layer is uncertain.

Considerations to remember on piggy-backing:

•Installing a piggy-back system is more costly than the installation of a sin-

gle anchor.

•If the mooring line of the second anchor is connected to the rear of the

first anchor, the stability, penetration and holding capacity of the first

anchor may be less than is the case for a single anchor. The force from the

second anchor may tend to pull the fluke of the first anchor closed (hing-

ing type anchors).

•If the piggy-back anchor is connected to the first anchor by means of a

chaser, the chaser may obstruct penetration of the first anchor.

•Both anchors must be exactly in line with the mooring line load. The lead

anchor may become unstable if a lateral load is applied.

•Two hinging anchors in piggy-back do not provide 2 times but only 1 to 1.6

times the individual holding capacity of the two anchors, for reasons

described in second point above.

Piggy-back methods 87

fig. 3-60

•If the first anchor is not influenced by the pull from the second anchor, and

the second anchor (fixed fluke/shank type anchors) is connected at 3 to 4

shank lengths distance from the first anchor, the holding capacity of the 2

anchors may be up to 2.5 times the holding capacity of the individual

anchors, due to the extra penetration of the second anchor.

Piggy-backing involving hinging anchors

Since there is little difference between handling one hinging anchor or two,

the first method is described with a Stevin anchor (hinging) in combination

with a Stevpris anchor (non-hinging). Here, the Stevpris is main anchor and

the Stevin is back-up. This is the best solution when using a fixed shank

anchor as the fluke of the Stevpris anchor can not be pulled closed. The pendant

line is connected to the padeye near the anchor shackle so performance is

not reduced. Note: if the piggy-back anchor can not be laid in line with the

mooring load, the piggy-back anchor makes the main anchor unstable. In

such a case the Stevpris can better be placed as the second anchor.

For optimal performance of the combination, the pendant line between

the two anchors should be wire rope, to promote penetration and obtain

better holding capacity (fig. 3-60).

Piggy-back methods

The installation procedure is described as follows:

•Pay out the main anchor as usual.

•Tension the mooring line until the anchor slips.

•Connect the second anchor to the pendant line.

•Bring the anchor to its location.

•Lower the piggy-back anchor and tension the mooring line again.

•Provide the pendant of the second anchor with a buoy for easy retrieval.

Piggy-backing with two Stevpris anchors

When two Stevpris anchors are used in piggy-back, the holding capacity of

the combination may be equal or higher than the sum of the individual

holding capacities of the anchors. The installation procedure of two

Stevpris anchors in piggy-back is as follows:

•Pay out the main Stevpris anchor, with the mooring line connected to the

anchor shackle and the pendant line (wire rope for optimal performance

and approximately three times the shank length of the first Stevpris

anchor) connected to the padeye behind the anchor shackle.

•Connect the other end of the pendant line to the anchor shackle of the

second Stevpris anchor (fig. 3-62).

•To lower the second Stevpris anchor to the seabed, a second pendant line

is connected to the padeye behind the anchor shackle.

•Using the second pendant line, the Stevpris anchors are lowered to the

seabed and positioned and buoyed off.

•The Stevpris anchors are then tensioned by pulling on the mooring line

(fig. 3-61).

fig. 3-62

Piggy-back methods 89

fig. 3-63

fig. 3-61

Piggy-backing by using a chaser

Sometimes chasers are used to connect the piggy-back anchor to the first

anchor (fig. 3-63), although a pendant line connected directly to the padeye

behind the main anchor shackle of the first anchor is prefered.

The installation procedure described for two Stevpris anchors is also applic-

able when a chaser is used for the connection.

During the deployment of the piggy-back combination, care must be taken

that anchors are installed in line with the load.

Stevmanta VLA installation

Introduction

The Stevmanta VLA consists of an anchor fluke which is connected with

wires to the angle adjuster. The angle adjuster is responsible for changing

the anchor from the installation mode to the vertical (or normal) loading

mode.

There are many options to install VLA anchors. The most efficient methods

are based on two different principles:

•Double line installation method using the fixed angle adjuster.

•Single line installation method using the shear pin angle adjuster.

The double line installation method is typically used when it is preferable

to install the anchor with a steel wire rope installation line instead of using

the actual mooring line (for example polyester).

The following three typical methods for installing the Stevmanta VLA are

discussed:

•Single line installation method.

•Double line installation method.

•Double line installation method using the Stevtensioner.

It is also possible to use the Stevtensioner with the single line installation

method, however because this is very similar to the double line installation

method with Stevtensioner, it is not presented here.

fig. 3-64

installation mode

shear pin

fig. 3-65

normal mode

Single line installation procedure

This procedure requires only one AHV for installation of the Stevmanta. The

Stevmanta is deployed with the shearpin angle adjuster. The mode of the

anchor changes when the shearpin breaks at a load equal to the required

installation load. When the shear pin breaks, the Stevmanta changes from

the installation mode to the normal (vertical) loading mode (fig. 3-64 and

fig. 3-65).

Installation procedure

In the installation procedure an optional tail has been included on the

Stevmanta. The tail assists in orientation of the Stevmanta on the seabed.

Connect the installation/mooring line to the angle adjuster on the

Stevmanta on the AHV. Lower the Stevmanta overboard. The Stevmanta

will decend tail first, i.e. the tail will be the first part to reach the seabed (fig.

3-66).

When the Stevmanta is on the seabed, an ROV can optionally inspect the

anchor (position and orientation). The AHV starts paying out the installa-

tion/ mooring line while slowly sailing away from the Stevmanta (fig. 3-67).

Stevmanta VLA installation 91

fig. 3-66

tail for

orientation

recovery

fig. 3-67

ROV

Stevmanta VLA installation

When enough of the installation/mooring line has been paid out, the AHV

starts increasing the tension in the installation line. The Stevmanta will start

to embed into the seabed (fig. 3-68).

When the predetermined installation load has been reached with the AHVs

bollard pull, the shearpin in the angle adjuster fails, triggering the

Stevmanta into the normal (vertical) loading mode. This can be clearly

noticed on board the AHV, as the AHV will stop moving forward due to the

sudden increase in holding capacity. Now that the Stevmanta is in the

normal (vertical) loading mode, the AHV can continue to increase the ten-

sion in the (taut-leg) installation/mooring line up to the required proof ten-

sion load (fig. 3-69).

fig. 3-68

fig. 3-69

After the Stevmanta has been proof tensioned to the required load, the

installation/mooring line can be attached to the floater.

In case of a pre-laid mooring, the mooring line can be buoyed off, for easy

connection later on (fig. 3-70).

Stevmanta retrieval

The Stevmanta is easily retrieved by pulling on the ‘tail’. Connection to the

tail can be achieved either with a grapnel or by using an ROV (fig. 3-71).

Stevmanta VLA installation 93

fig. 3-70

fig. 3-71

Stevmanta VLA installation

Alternatively the Stevmanta can be equipped with an optional recovery sys-

tem. The recovery system consists of two special sockets which connect the

front wires to the fluke.

To recover the anchor, the mooring line is pulled backwards, i.e. away from

the centre of the mooring. Once the mooring line has been pulled back, the

front sockets will disconnect from the fluke (fig. 3-72).

The Stevmanta VLA is now pulled out of the soil using just the rear wires.

This reduces the resistance of the anchor, so that it can be retrieved with a

load equal to about half the installation load (fig. 3-73).

fig. 3-72

pull for retrieval

fig. 3-73

retrieval

Double line installation procedure

This procedure requires two AHVs. The Stevmanta is deployed with the

fixed angle adjuster. The mode of the anchor (installation mode or normal

(vertical) loading mode) is chosen by pulling on either the installation line

or the mooring line.

The Stevmanta is in the installation mode when the installation line is ten-

sioned, i.e. the line on the front of the angle adjuster (fig. 3-74).

The Stevmanta is in the normal (vertical) loading mode when the mooring

line is tensioned, i.e. the line on the rear of the angle adjuster (fig. 3-75).

During the installation AHV1 handles the steel installation line and AHV2

handles the mooring line, for instance polyester (fig. 3-76).

In the installation procedure an optional subsea recovery buoy can be

included in the installation line. The recovery buoy is connected to the

installation line via a delta plate at approximately 90 m from the Stevmanta

(fig. 3-77).

Stevmanta VLA installation

fig. 3-74

installation mode

installation line

mooring line

fig. 3-75

normal mode

mooring line

installation

line

fig. 3-76

AHV2 AHV1

fig. 3-77

AHV2 AHV1

Stevmanta VLA installation

fig. 3-78

AHV2 AHV1

fig. 3-79

AHV2

break

link

breaks

AHV1

fig. 3-80

AHV2

pretension load

recovery

line

Connect the installation line to the angle adjuster on the Stevmanta on

board AHV1.

Pass the mooring line from AHV2 to AHV 1 and connect it to the angle

adjuster.

Lower the Stevmanta VLA overboard by keeping tension on both the instal-

lation line (AHV1) and the mooring line (AHV2).

When the Stevmanta is on the seabed, an ROV can inspect the anchor’s posi-

tion and orientation. AHV2 slackens the tension in the mooring line and

AHV1 starts paying out the installation line while slowly sailing away from

the Stevmanta (fig. 3-78).

When enough of the installation line has been paid out, AHV1 starts

increasing the tension. The Stevmanta will start to embed into the seabed.

AHV2 keeps the mooring line slack by keeping the same distance from

AHV1. If more bollard pull is required than one AHV can deliver, AHV2 can

buoy off the mooring line and pull with AHV1 in tandem.

When the predetermined installation load has been reached, the breaking

device in the installation line fails (break shackle connecting the installation

line to the delta plate), freeing the installation line from the Stevmanta (fig.

3-79).

If the optional recovery buoy is used, the breaking device is placed on the

delta plate connecting it to the installation line and AHV1. AHV1 is now no

longer connected to the Stevmanta and the installation line can be recov-

ered on deck (fig. 3-80).

AHV2 can now start increasing the tension in the mooring line. If AHV2 can

not generate enough bollard pull to reach the required proof tension load,

AHV1 can be connected in tandem to AHV2 to generate additional bollard

pull.

After the Stevmanta has been proof tensioned to the required load, the

mooring line can be attached to the floater.

In case of a pre-laid mooring, the mooring line can be buoyed off, for easy

connection later on (fig. 3-81).

Stevmanta retrieval

The Stevmanta is recovered from the seabed by returning to ‘installation

mode’ instead of the normal (vertical) loading mode. The AHV picks up the

recovery buoy from the seabed and by pulling on the installation load at an

angle of approximately 450 with the seabed, the anchor is easily retrieved

(fig. 3-82).

Stevmanta VLA installation

fig. 3-81

AHV2

fig. 3-82

AHV2AHV2

Stevmanta VLA installation 98

Single line installation with Stevtensioner

The Stevmanta VLA is deployed with the shearpin angle adjuster. The mode

of the anchor changes when the shearpin breaks at a load equal to the

required installation load. When the shear pin breaks, the Stevmanta VLA

changes from installation mode to the normal (vertical) loading mode.

In the installation procedure a tail (approximately 30 m length, consisting of

a length of wire with approximately 5 m of chain on the end) has been

included on the Stevmanta VLA. The tail assures correct orientation of the

Stevmanta VLA on the seabed.

Connect the tail to the rear of the fluke of the Stevmanta VLA #1. Connect

the forerunner to the angle adjuster of the Stevmanta VLA on the AHV.

Lower Stevmanta VLA #1 overboard (fig. 3-83). The Stevmanta VLA will be

going downwards tail first, i.e. the tail will be the first part that reaches the

seabed.

Connect the tensioning chain to the forerunner on Stevmanta VLA #1 using

the subsea connector and pass the other end through the Stevtensioner.

This end of the chain is terminated with a male part of the subsea connector.

fig. 3-83

Stevmanta VLA installation 99

Connect the forerunner of Stevmanta VLA #2 to the passive side of

the Stevtensioner. As part of the forerunner a tri-plate is included with a

breaklink between the Stevtensioner and the tri-plate. The male part of a

subsea connector is connected to the third hole of the tri-plate. Connect the

AHV work-wire to the tail of Stevmanta VLA #2 using a subsea connector.

Deploy the Stevtensioner and Stevmanta VLA #2 overboard by slacking the

AHV workwire (fig. 3-84 and fig. 3-85).

fig. 3-85

fig. 3-84

Stevmanta VLA installation 100

fig. 3-86

fig. 3-87

When the tail of Stevmanta VLA #1 touches the seabed, the resistance of

the tail will orient the Stevmanta in the heading of the AHV which is

moving forward slowly. The AHV places the Stevmanta on the seabed and

continues with the deployment of the rest of the system (Stevtensioner and

Stevmanta VLA #2) (fig. 3-86).

When Stevmanta VLA #2 is near the seabed, the AHV stops the winch and

increases the tension in the mooring system (fig. 3-87). This will start to

embed Stevmanta VLA #1. When a tension of approximately 1000 kN has

been reached, the AHV can lay down Stevmanta VLA #2 on the seabed.

The purpose of the applied tension is to ensure that Stevmanta VLA #1

is embedding properly and to take the slack out of the system.

Stevmanta VLA installation 101

fig. 3-89

fig. 3-90

When Stevmanta VLA #2 has been placed on the seabed, the AHV continues

to deploy the work wire until the tail and the subsea connector are on the

seabed. When this has been accomplished, the AHV stops paying out the

work wire and the ROV is sent down to disconnect the subsea connector

from the tail on Stevmanta VLA #2. The female part of the subsea

connector (connected to the work wire) is then moved to the male part of

the subsea connector connected to the tensioning chain above the

Stevtensioner (fig. 3-88).

With the work wire now connected to the tensioning chain, the AHV can

start the tensioning operation. This will generally consist of 4 to 7 yo-yo

procedures to reach the required tension at the anchors. (fig. 3-89 and fig. 3-90).

fig. 3-88

Stevmanta VLA installation 102

When the tension in the system reaches the break load of the shear pins in

the angle adjuster of the Stevmanta VLAs, these will break and trigger the

Stevmanta VLAs to their normal loading mode (fig. 3-91). When the AHV

continues to increase the tension in the system, the anchors will be proof

loaded in their normal loading mode. After the proof loading of the

anchors, the AHV increases the tension in the system up to the point were

the breaklink connecting the passive line to the Stevtensioner fails. The

tensioning of the anchors is now complete.

With the tensioning of the anchors completed, the ROV disconnects the

subsea connector between Stevmanta VLA #1 and the Stevtensioner (fig. 3-

92). The anchor forerunners are now no longer connected to the

Stevtensioner. The AHV can start recovering the Stevtensioner with the

tensioning chain by winching in the work wire (fig. 3-93). The ROV can be

used to connect the mooring lines (with separate female connectors) to the

male connectors on the anchor forerunners.

fig. 3-91

fig. 3-92

fig. 3-93

Stevmanta VLA installation 103

Double line installation with Stevtensioner

The Stevmanta is deployed with the fixed angle adjuster. The mode of the

anchor (installation mode or normal (vertical) loading mode) is chosen by

pulling on either the installation line or the mooring line. The Stevmanta

is in the installation mode when the installation line is tensioned, i.e. the

line on the front of the angle adjuster (fig. 3-94).

The Stevmanta is in the normal (vertical) loading mode when the mooring

line is tensioned, i.e. the line at the rear of the angle adjuster. During the

installation AHV1 handles the installation line (preferably chain and steel

wire) and AHV2 handles the mooring line, for instance polyester (fig. 3-95).

The installation procedure with the Stevtensioner requires a reaction

anchor (the typical use of the Stevtensioner is presented in the next

chapter). In this case the reaction anchor can be either a Stevpris or

Stevmanta. For now a Stevpris is shown as reaction anchor and is to be on

the active side of the Stevtensioner.

fig. 3-84

normal mode

mooring line

installation

line

fig. 3-83

installation mode

installation line

mooring line

Stevmanta VLA installation 104

fig. 3-86

stopper

work chain AHV1AHV2

fig. 3-85

tensioner AHV1AHV2

Connect the installation line to the angle adjuster on the Stevmanta on

AHV1. Pass the mooring line from AHV2 to AHV1 and connect it to the

angle adjuster.

Lower the Stevmanta to the seabed by keeping tension on both the instal-

lation line and mooring line.

Connect the installation line to the passive side of the Stevtensioner.

A break link can be installed between the Stevtensioner and the installation

line on the passive side (fig. 3-96).

Connect the installation line to the reaction anchor. Pass the installation

line through the Stevtensioner (fig. 3-97).

Stevmanta VLA installation 105

Sail to set-down position of the reaction anchor (AHV1 only). AHV2 stays above the Stevmanta.

During the movement of AHV1, the installation line of the Stevmanta has to be paid out (fig. 3-98).

Lower the Stevtensioner and reaction anchor to the seabed (fig. 3-99).

Buoy off the retrieval line (or mooring line) of the reaction anchor. AHV1 sails to tensioning point

and starts taking in the slack of the tensioning line (fig. 3-100).

fig. 3-89

AHV2 AHV1

wire

chain

stopper

tensioner stopper

fig. 3-88

AHV2 AHV1

chain

stopper

wire

tensioner stopper

fig. 3-87

AHV2 AHV1

chain

stopper

wire

shark jaws

tensioner

Stevmanta VLA installation 106

Start the tensioning procedure (yo-yoing) (fig. 3-101).

The break link will break on the Stevmanta when the required installation

load has been reached (fig. 3-102).

fig. 3-91

AHV2 AHV1

wire

chain

stopper

tensioner

break link breaks stopper

fig. 3-90

AHV2 AHV1

wire

chain

stopper

tensioner

stopper

Stevmanta VLA installation 107

Recover the Stevtensioner, the installation line and the reaction anchor to

AHV1.

AHV2 can now proof tension the Stevmanta and then buoy off the mooring

line. Installation of the Stevmanta is now complete (fig. 3-103).

Instead of using a reaction anchor, two Stevmantas can also be installed at

the same time. After completion of the tensioning (yo-yoing), AHV2 proof

tensions one Stevmanta while AHV1 recovers the Stevtensioner and

disconnects it from the installation line of the other Stevmanta. This

Stevmanta can then also be proof tensioned (fig. 3-104).

fig. 3-92

AHV2 AHV1

wire

chain

tensioner

pretension load stopper

fig. 3-93

AHV2 AHV1

wire

chain

stopper

tensioner stopper

The Stevtensioner 108

Introduction

The Stevtensioner is used for cross tensioning of diametrically opposed

anchor legs moored by drag anchors or anchor piles. The Stevtensioner is

generally used for the installation of (semi) permanent floating structures

such as the SPM buoy, STL, TLP, FPS, FPSO, etc. After the tensioning opera-

tions the Stevtensioner is demobilised and ready for the next project. The

Stevtensioner can however also be used for permanent tensioning purposes,

becoming a part of the mooring system. The Stevtensioner can be deployed

from a crane barge, AHV or any vessel having enough crane/winch capacity

to pull the required vertical force. The existing models VA220 and VA500

were designed for handling a single size of chain. The new Stevtensioner

models VA600, VA1000 and VA1250 can handle chain diameter ranging

from 76 mm up to 152 mm. Because of this variety in chain sizes additional

work chain may not be required (fig. 3-105).

he working principle of the tensioner

The Stevtensioner is based on the principle that a vertical load to a horizontal

string causes high horizontal loads. To achieve the required horizontal

pretension load at the anchor points, the vertical pulling force only needs to be

40% of this pretension. The anchor line tension is measured by a measuring pin

located inside the Stevtensioner and as such well protected against damage

caused by handling and lifting operations (fig. 3-106).

fig. 3-94

fig. 3-95

The new Stevtensioner models

offer the following features:

• Smaller dimensions, reduced weight and

improved handling, but heavy enough to

easilty slide down the mooring line.

• Designed to smoothly guide at least 5 links and

therefore prevent chain getting stuck inside.

• Due to economical volume/weight ratio,

the new Stevtensioner models allow for

containerised freight by either sea or,

for rush deliveries, by air.

• The integrated shape allows for smooth passage

over stern roller.

• Load measuring pin is equipped with two

independent sets of strain gauges. The umbilical

cable connections are protected against han-

dling and lifting operations. These connections

may be used for acoustic transfer of the signals.

The Stevtensioner 109

One anchor line (passive line) is attached to the tension measuring pin at the Stevtensioner. The

oppos-ite anchor line (active line) passes through the Stevtensioner. Tensioning starts by apply-

ing the yo-yo movement to the active line (fig. 3-107).

When the Stevtensioner is lifted by the active chain, it blocks the chain. When the Stevtensioner

is lifted from the seabed, the passive and active mooring lines are also lifted. Consequently the

anchors or piles are loaded and cause an inverse catenary of the mooring line in the soil, as well

as causing the anchor to drag and embed. In other words: chain length is gained. Lowering the

Stevtensioner slackens the anchor lines and allows it to slide down over the active chain. By

repeating this several times (called the yo-yo movement), the horizontal load on the anchor

points increases. Generally the required horizontal load is achieved after 5 to 7 steps. Once

tensioning is completed, the Stevtensioner is recovered by pulling the lifting/pennant wire making it

disengage. This allows the Stevtensioner to slide up along the active chain to the surface (fig. 3-108).

chain locks

fig. 3-108

active chainpassive chain

fig. 3-107

The Stevtensioner 110

Measurement of the tensions applied

Fig. 3-109 shows the curve recorded during tensioning of chains connected

to piles for the Coveñas Pipeline Project in Colombia. The graph shows a

total of 5 heaves (yo-yo’s), each resulting in a higher tension.

When the Stevtensioner is lifted from the seabed, the passive and active

mooring lines are also lifted from the seabed. Consequently the anchors or

piles are loaded. The loading causes an inverse catenary of the mooring line

in the soil, and also causes the anchor to drag and embed; in other words:

chain length is gained. When lowering to seabed the gain in chain length

(slack) is won by the Stevtensioner sliding down the chain (approximately

5 to 8 links). The next heave (yo-yo) will therefore create a higher tension in

the system. In practise a total of 5 to 7 yo-yos are required to reach the

required proof tension load.

Different methods can be applied to verify the tension in the chain.

These are discussed below.

fig. 3-98

tension force in t

250

125

030 6090120

time in minutes

tension on anchor

lifting force

The Stevtensioner 111

Computer calculations

The tension in the chain can be calculated by means of computer catenary

calculations. Besides known parameters such as submerged chain weight,

and the length of the mooring line, other parameters measured during ten-

sioning need to be incorporated in the calculation:

•Height Stevtensioner above seabed.

•Vertical pulling load.

By using this method the tension in the chain can be calculated at any

height of the Stevtensioner above seabed. This method is independent of

the waterdepth.

Umbilical cable and measuring pin

The chain tension can be measured with a measuring pin. The pin is part of

the Stevtensioner housing and is equipped with strain gauges. The pin is

connected to a tension read-out unit on the installation vessel by using an

umbilical cable. The pin is connected to the passive chain. All tensioning data

are measured on deck and presented during tensioning on a chart recorder.

A hand winch with sliding contacts is used to veer and haul the umbilical

without disconnecting the umbilical from the registration equipment. The

measurement is insensitive for variations in cable length. The use of an

umbilical is an effective method in waterdepths down to approximately 200

meters. Beyond this depth it becomes more efficient to use either an acoustic

system or computer calculations.

Break-link

The passive chain can be attached to the Stevtensioner by a break-link.

When, during the tensioning operation, a predetermined load has been

reached, the link breaks. Consequently the passive chain falls to the bottom,

and the Stevtensioner can be retrieved.

The Stevtensioner 112

Duration of pretensioning anchors and piles

Once the required tension has been achieved, the tension has to be main-

tained for a certain duration. This period is described in the table below for

various Certification Authorities.

Certification Authority Required duration of

maintaining tension

Lloyds Register of Shipping 20 minutes

American Bureau of Shipping 30 minutes

Det Norske Veritas (NMD) 15 minutes

The Stevtensioner 113

fig. 3-99

fig. 3-100

Handling the Stevtensioner

Handling operations can generally be described as follows:

•Positioning the anchors and paying out the chain

•Hook-up all necessary hardware for tensioning operations on deck of

barge or AHV

•Deployment Stevtensioner to the seabed and positioning of the installa-

tion vessel

•First lift (yo-yo)

•Series of yo-yo’s

•Maintain required tension for a specified period of time

•Retrieve the Stevtensioner and disconnect

•Prepare for next tensioning

A Stevtensioner can be deployed from a crane barge, Anchor Handling

Vessel or any vessel having enough crane/winch capacity to lift the required

vertical force.

General tensioning procedures

General tensioning procedures using crane barge or AHV for Stevtensioner

models VA1000 and VA1250 are presented in fig. 3-110 and 3-111.

The Stevtensioner 114

Hook-up

Pass the active chain (2) through the tensioner (1) on deck. Connect passive

chain (3) to measuring pin shackle (8). Connect dislock wire (5) to shackle

(4). Connect umbilical cable (7) to read-out system on deck and to the

measuring pin (6).

Lowering

Fix active chain (2) to winch or crane hook. Slack dislock wire (5) and lower

Stevtensioner to seabed. Stevtensioner will pass over active chain (2).

Tensioning mode

When Stevtensioner is on seabed, slack dislock wire (5) before the first yo-yo,

and keep slack during all yo-yos!

Tensioning is achieved by pulling on active chain (2). The mooring lines will

be lifted from the seabed causing the anchors or piles to be loaded. After

each yo-yo active chain is gained. The active chain can only pass through the

Stevtensioner in one direction. Approximately 4 to 7 yo-yos are required to

obtain the required pretension load (fig. 3-111).

fig. 3-100

The Stevtensioner 115

Retrieving

When tensioning is completed be sure to lower the Stevtensioner to seabed

and slack off active chain (2) before retrieving Stevtensioner with dislock

wire (5). Pull on dislock wire (5). Stevtensioner will pass over chain (2).

Disconnect Stevtensioner on deck of the barge or AHV.

Stevtensioner Product Range

The following Stevtensioners are available from vryhof anchors.

Stevtensioner Maximum Suitable* for chain Suitable* for chain Size Weight

model horizontal load size with Kenter size without Kenter Stevtensioner Stevtensioner

[t] shackle [mm] shackle [mm] lxhxw [m] [t]

VA 220 220 50 60 2.6 x 1.2 x 1.0 5

VA 500 500 102 112 5.4 x 2.6 x 2.4 20

VA 600 600 76 - 84 76 - 87 2.2 x 0.9 x 0.6 2.5

VA1000 1000 102 - 117 102 - 135 3.1 x 1.2 x 0.8 6

VA1250 1250 114 - 132 114 - 152 3.5 x 1.4 x 0.9 9

* The suitability only refers to the section of chain passing through the Stevtensioner. Chain or wire not passing through the

Stevtensioner may have any dimension.

Supply/anchor handling vessels 116

Drilling rigs are generally moored with 8 to 12 anchors. These are laid in a

mooring pattern. Originally normal tugs were used for these operations,

but very soon, there was a call for specialised vessels.

For anchor handling vessels, it is very important to be able to work quickly and

effectively. Much depends on the expertise of the captain and crew. The equip-

ment and its design are also extremely important. Engine power has to be suf-

ficient to handle chain and/or wire and anchors at the water depth concerned.

The newest generation of AHVs has bollard pulls far in excess of 200 t.

Care should be given to the rated maximum bollard pull which in reality

might be less, depending on the use of other power consuming equipment

such as bow (and sometimes) stern thrusters, winches, etc.

The winch often causes confusion. An AHV owner demonstrates maximum

pulling capacity at the bare drum during the maiden trip, but a contractor

requires high winch output when the drum is 70 to 100% wound with wire

under working conditions. It is also possible that an owner limits the

pressure of the hydraulic system below factory limits, to reduce winch wear

and repair costs.

The dynamic capacity of the winch brake is particul-arly important when a

long heavy chain must be deployed. Hydraulically and electrically braked

drums are more efficient than band brakes.

For handling chain, many supply vessels have chain lockers below decks and

a wildcat above the chain locker.

To ensure easy handling of chain and wire, simple, well-constructed tools

are necessary. An experienced crew will also make the handling easier.

These specialised anchor handling vessels

(AHVs) now have:

• A large deck space.

• Powerful winches, with auxiliary winches to reel

extra wires.

• Large chain lockers, for storage of the chain.

• Large wire storage capacity.

• An adapted seaworthy design and very

manoeuvrable with bow and stern thrusters.

Some even with a dynamic positioning system.

• Space for drilling mud and fuel tanks for

supply to drilling rigs.

• Small auxiliary cranes.

• One or two sets of towing pins and shark jaws.

• A stern roller that sometimes consists of

two individually rotating drums.

table P

Product data

Introduction 118

Product Data

In this editon of the vryhof anchor manual, we have given the reader as

much information and data as we imagined would normally be needed.

Undoubtedly some is missing. This can be vryhof-specific or general

information. Vryhof-specific, information can be related to brochures,

detailed handling recommendations and product data. This can be

obtained on request, while general information will also be provided if

available.

To make the next edition of the anchor manual suit the requirements of the

reader even better than this one, your suggestions of comments are much

appreciated.

Dimensions of vryhof anchor types

Dimensions

Stevin Mk3

119

Stevin Mk3

Dimensions 120

Dimensions of vryhof anchor types

Note: The dimensions of the Stevin Mk3 anchor may be changed for specific applications

Main dimensions Stevin Mk3 dimensions in mm anchor weight in kg

weight 1000 1500 3000 5000 7000 9000 12000 15000 20000 30000

A2429 2774 3493 4120 4602 5012 5516 5942 6372 7289

B2654 3038 3828 4538 5077 5521 6076 6545 6986 7997

C1559 1785 2249 2667 2983 3244 3570 3846 4100 4694

D2023 2316 2918 3460 3871 4209 4632 4990 5324 6094

E737 843 1063 1260 1409 1533 1687 1817 2048 2345

K1010 1156 1456 1727 1932 2100 2312 2490 2674 3061

L412 471 594 704 788 857 943 1016 1083 1240

S60 65 80 80 90 100 110 120 160 180

Stevin Mk3

Dimensions 121

Main dimensions of vryhof anchor types

Stevpris Mk5Stevpris Mk5

Dimensions 122

Main dimensions of vryhof anchor types

sand

mud

Stevpris Mk5

Main dimensions Stevpris Mk5 dimensions in mm anchor weight in kg

weight 1500 3000 5000 8000 10000 12000 15000 18000 20000 22000 25000 30000 65000

A2954 3721 4412 5161 5559 5908 6364 6763 7004 7230 7545 8018 10375

B3184 4011 4756 5563 5992 6368 6860 7290 7550 7794 8133 8643 11184

C1812 2283 2707 3166 3410 3624 3904 4149 4297 4436 4629 4919 6365

E1505 1896 2248 2629 2832 3010 3242 3446 3569 3684 3844 4085 5286

F271 342 406 474 511 543 585 622 644 665 694 737 954

H1230 1550 1837 2149 2315 2460 2650 2816 2917 3011 3142 3339 4321

T493 622 738 862 929 988 1064 1131 1171 1209 1262 1341 1736

S80 90 110 130 140 150 170 180 190 200 200 220 300

Note: The dimensions of the Stevpris Mk5 anchor may be changed for specific applications

Dimensions 123

Transport dimensions of vryhof anchor types

Stevpris Mk5Stevpris Mk5

Dimensions 124

Transport dimensions of vryhof anchor types

Note: The dimensions of the Stevshark Mk5 anchor may be changed for specific applications

Transport dimensions Stevpris Mk5 dimensions in mm weight in kg

weight

anchor 1500 3000 5000 8000 10000 12000 15000 18000 20000 22000 25000 30000 65000

fluke 600 1300 2100 3400 4300 5200 6400 7700 8600 9400 10700 12900 27900

shank 900 1700 2900 4600 5700 6800 8600 10300 11400 12600 14300 1 7100 37100

B3184 3999 4750 5550 5980 6348 6848 7278 7547 7799 8123 8650 11193

C1812 2283 2707 3166 3411 3625 3904 4149 4297 4436 4629 4919 6365

D2367 2969 3529 4122 4442 4714 5087 5407 5609 5799 6035 6431 8322

H1232 1538 1831 2140 2301 2443 2642 2808 2920 3016 3135 3345 4328

T494 623 739 864 930 989 1065 1132 1172 1210 1263 1342 1737

U3294 4141 4913 5747 6190 6578 7090 7533 7806 8060 8406 8936 11563

V1221 1526 1817 2120 2285 2422 2618 2783 2891 2994 3108 3321 4297

W984 1240 1470 1719 1852 1968 2120 2253 2334 2409 2514 2671 3456

Stevpris Mk5

Main dimensions of vryhof anchor types

Dimensions 125

Stevspris Mk6

Dimensions

Main dimensions of vryhof anchor types

126

sand

middle

mud

Main dimensions Stevspris Mk6 dimensions in mm anchor weight in kg

weight 1500 3000 5000 8000 10000 12000 15000 18000 20000 22000 25000 30000

A2797 3523 4178 4886 5263 5593 6025 6402 6631 6845 7143 7591

B3059 3870 4602 5390 5807 6171 6679 7101 7368 7625 7962 8451

C1981 2495 2958 3460 3728 3961 4267 4534 4696 4848 5059 5376

E1321 1664 1973 2308 2486 2642 2846 3024 3132 3234 3374 3586

F641 808 958 1120 1206 1282 1381 1468 1520 1569 1637 1740

H1170 1490 1781 2090 2253 2394 2610 2777 2890 3002 3138 3324

S65 80 100 120 130 140 160 170 180 190 200 210

Note: The dimensions of the Stevspris Mk6 anchor may be changed for specific applications

Stevspris Mk6

Transport dimensions of vryhof anchor types

Dimensions 127

Stevspris Mk6

Note: The dimensions of the Stevspris Mk6 anchor may be changed for specific applications

Transport dimensions Stevspris Mk6 dimensions in m anchor weight in kg

weight 1500 3000 5000 8000 10000 12000 15000 18000 20000 22000 25000 30000

B3.06 3.87 4.60 5.39 5.81 6.17 6.68 7.10 7.37 7.63 7.96 8.45

Ct 1.98 2.49 2.95 3.45 3.72 3.95 4.26 4.52 4.69 4.84 5.05 5.36

Cs 1.96 2.47 2.93 3.43 3.69 3.92 4.23 4.49 4.65 4.80 5.01 5.32

H 1.17 1.49 1.78 2.09 2.25 2.39 2.61 2.78 2.89 3.00 3.14 3.32

Tt 0.78 0.98 1.16 1.36 1.46 1.55 1.68 1.78 1.84 1.90 1.99 2.11

Ts 0.70 0.88 1.04 1.22 1.31 1.39 1.50 1.59 1.65 1.70 1.78 1.89

U2.79 3.52 4.17 4.88 5.26 5.59 6.02 6.40 6.62 6.84 7.14 7.58

V1.21 1.54 1.83 2.15 2.32 2.46 2.69 2.86 2.97 3.09 3.23 3.42

W0.99 1.25 1.48 1.73 1.86 1.98 2.13 2.27 2.35 2.42 2.53 2.69

Dimensions

Transport dimensions of vryhof anchor types

128

truck

Stevspris Mk6

Dimensions 129

Stevshark Mk5

Dimensions 130

sand

mud

Note: The dimensions of the Stevshark Mk5 anchor may be changed for specific applications

Main dimensions Stevshark Mk5 dimensions in mm anchor weight in kg

weight 1500 3000 5000 8000 10000 12000 15000 18000 20000 22000 25000 30000 65000

A2862 3605 4275 4999 5385 5723 6165 6551 6785 7004 7309 7767 10051

B3085 3886 4608 5389 5805 6169 6645 7062 7314 7550 7879 8373 10834

C1755 2212 2622 3067 3304 3511 3782 4019 4163 4297 4484 4765 6166

E1458 1837 2178 2547 2743 2915 3140 3337 3457 3568 3723 3957 5120

F263 332 393 460 495 526 567 602 624 644 672 714 924

H1192 1502 1780 2082 2243 2383 2567 2728 2826 2917 3044 3235 4186

T478 603 715 836 900 957 1031 1095 1135 1171 1222 1299 1681

S80 90 110 130 140 150 160 170 180 190 200 210 300

131

Dimensions

Dimensions of vryhof anchor types

Stevmanta VLA - permanent

Dimensions

Dimensions of vryhof anchor types

Note: The dimensions of the Stevmanta VLA anchor may be changed for specific applications

E1 E0

Stevmanta VLA - permanent

132

Main dimensions Stevmanta VLA dimensions in mm area in m2

area 5810 12 15 17 20

B3143 3975 4445 4869 5443 5795 6286

C2976 3765 4209 4611 5155 5488 5953

D1945 2460 2750 3013 3368 3586 3890

E0 3075 3890 4349 4764 5326 5670 6150

E1 3371 4264 4767 5222 5839 6216 6742

F172 217 243 266 298 317 344

H1459 1845 2063 2260 2527 2690 2918

T639 809 904 991 1107 1179 1279

Dimensions of vryhof anchor types

Dimensions 133

Stevmanta VLA - MODU

Dimensions

Dimensions of vryhof anchor types

134

Note: The dimensions of the Stevmanta VLA anchor may be changed for specific applications

Main dimensions Stevmanta VLA dimensions in mm area in m2

area 5810 12 15 17 20

B3143 3975 4445 4869 5443 5795 6286

C2976 3765 4209 4611 5155 5488 5953

D1945 2460 2750 3013 3368 3586 3890

E0 3075 3890 4349 4764 5326 5670 6150

E1 3371 4264 4767 5222 5839 6216 6742

F172 217 243 266 298 317 344

H1459 1845 2063 2260 2527 2690 2918

T639 809 904 991 1107 1179 1279

Stevmanta VLA - MODU

Dimensions other anchor types 135

Danforth

weight AB C D

lb. kg mm mm mm mm

1000 454 1830 1580 410 1100

2500 1134 2260 2140 560 1350

5000 2268 2780 2700 710 1650

10000 4536 3510 3330 890 2100

12000 5443 3730 3540 945 2240

14000 6350 3920 3720 995 2360

16000 7257 4100 4000 1040 2470

20000 9072 4370 4150 1110 2620

25000 11340 4710 4470 1195 2820

30000 13608 5000 4750 1270 3000

Flipper Delta

weight AB C D

lb. kg mm mm mm mm

2205 1000 2605 1960 740 1560

5512 2500 3150 2660 1005 2130

11023 5000 3945 3300 1260 2660

16535 7500 4565 3850 1435 3080

22046 10000 5040 4270 1600 3400

26455 12000 5335 4530 1705 3600

33069 15000 5735 4845 1830 3875

44092 20000 6405 5410 2010 4320

71650 32500 7320 6200 2310 4930

88185 40000 7850 6650 2480 5290

Dimensions other anchor types 136

LWT

weight AB C D

lb. kg mm mm mm mm

1000 454 1905 1803 622 1168

5000 2268 2997 2845 984 1829

10000 4536 3658 3480 1245 2235

15000 6804 3988 3791 1362 2438

20000 9072 4394 4166 1499 2692

25000 11340 4851 4521 1708 2946

30000 13608 5029 4801 1715 3073

35000 15876 5283 5055 1803 3226

40000 18144 5537 6096 1905 3327

60000 27216 6350 7061 2184 3810

Moorfast

weight AB C D

lb. kg mm mm mm mm

1000 454 1549 1905 483 940

6000 2722 2565 3632 787 1549

10000 4536 3327 3988 1041 2032

12000 5443 3531 4242 1092 2159

16000 7257 3886 4750 1219 2388

20000 9072 4166 4978 1295 2591

30000 13608 4801 5512 1499 2997

40000 18144 5436 6299 1600 3226

50000 22680 5639 6528 1676 3353

60000 27216 5893 6883 1778 3556

Dimensions other anchor types 137

Stato

weight AB C D

lb. kg mm mm mm mm

3000 1361 3277 2769 860 1829

6000 2722 3658 3632 960 2337

9000 4082 4064 4318 1090 2540

15000 6804 5182 5690 1370 3200

20000 9072 5334 5842 1420 3277

25000 11340 5740 6248 1540 3480

30000 13608 5969 6528 1570 3683

35000 15876 6299 6883 1670 3886

40000 18144 6553 7188 1750 4064

60000 27216 7540 8120 2000 4570

AC14

weight AB C D

lb. kg. mm mm mm mm

2844 1290 2025 1568 470 1067

4630 2100 2382 1844 553 1255

6746 3060 2700 2091 627 1423

12368 5610 3305 2559 768 1741

18298 8300 3793 2916 875 1984

23149 10500 4073 3154 946 2146

29762 13500 4429 3249 1029 2333

41447 18800 4946 3829 1149 2606

44092 20000 5049 3909 1173 2660

50706 23000 5290 4095 1229 2787

138

Dimensions other anchor types

US Navy Stockless

weight AB C D

lb. kg mm mm mm mm

1000 454 1072 841 521 772

5000 2268 1854 1437 889 1319

10000 4536 2337 1810 1121 1661

15000 6804 2680 2089 1295 1861

20000 9072 2946 2280 1413 2094

25000 11340 3175 2456 1522 2256

30000 13608 3372 2608 1616 2394

35000 15876 3550 2743 1703 2523

40000 18144 3708 2872 1778 2619

60000 27216 4775 3194 2218 3375

Proof load test 139

Proof load test for HHP anchors (US units)

anchor proof anchor proof anchor proof

weight load weight load weight load

lbs kips lbs kips lbs kips

100 6.2 4100 92.5 10000 165.8

125 7.3 4200 94.2 11000 174.5

150 8.2 4300 95.9 12000 184.8

175 9.1 4400 97.5 13000 194.7

200 9.9 4500 99.1 14000 205.2

250 11.5 4600 100.7 15000 214.3

300 12.9 4700 102.3 16000 222.9

350 14.2 4800 103.9 17000 230.9

400 15.5 4900 105.5 18000 239

450 16.7 5000 107 19000 245

500 18.1 5100 108.5 20000 250.4

550 19.2 5200 110 21000 256.7

600 20.5 5300 111.4 22000 263.5

650 21.7 5400 112.9 23000 270.9

700 23 5500 114.4 24000 277.2

750 24.3 5600 115.9 25000 282.8

800 25.5 5700 117.4 26000 289.2

850 26.6 5800 118.7 27000 296.7

900 27.8 5900 120 28000 304.9

950 28.9 6000 121.4 29000 312.3

1000 29.8 6100 122.7 30000 318.9

1100 32.1 6200 124.1 31000 326.9

1200 34.5 6300 125.4 32000 333.7

1300 36.8 6400 126.8 33000 341.2

1400 39.1 6500 128.2 34000 348

1500 41.3 6600 129.5 35000 354.8

1600 43.5 6700 130.8 36000 361.6

1700 45.8 6800 132 37000 368.4

1800 48.2 6900 133.2 38000 375.2

1900 50.3 7000 134.4 39000 382

2000 52.3 7100 135.7 40000 388.8

2100 54.5 7200 136.9 42000 400.6

140

Proof load test

Proof load test for HHP anchors (US units)

anchor proof anchor proof anchor proof

weight load weight load weight load

lbs kips lbs kips lbs kips

2200 56.6 7300 138.1 44000 411.5

2300 58.6 7400 139.3 46000 425.1

2400 60.8 7500 140.6 48000 437

2500 62.8 7600 141.6 50000 449.1

2600 64.8 7700 142.7 52000 460.4

2700 66.8 7800 143.7 54000 472

2800 68.8 7900 144.7 56000 484.3

2900 70.7 8000 145.7 58000 496.5

3000 72.6 8100 146.8 60000 508.4

3100 74.5 8200 147.9 62000 519.3

3200 76.4 8300 149 64000 530.2

3300 78.3 8400 150 66000 541

3400 80.1 8500 151.1 68000 551.9

3500 81.9 8600 152.2 70000 562.8

3600 83.7 8700 153.2 75000 590

3700 85.5 8800 154.3 80000 617

3800 87.2 8900 155.2 82500 630

3900 89 9000 156.2

4000 90.7 9500 161.1

141

Proof load test

Proof load test for HHP anchors (SI units)

anchor proof anchor proof anchor proof

weight load weight load weight load

kg kN kg kN kg kN

50 29.7 2000 434.3 7000 970.3

55 31.7 2100 450 7200 987

60 34 2200 466 7400 1002

65 35.3 2300 480.7 7600 1018

70 37 2400 495 7800 1034

75 39 2500 509.7 8000 1050

80 40.7 2600 524.3 8200 1066

90 44 2700 537 8400 1078

100 47.3 2800 550.3 8600 1088.7

120 53 2900 563.7 8800 1099.3

140 58.3 3000 577 9000 1110

160 63.7 3100 589 9200 1120.7

180 68.4 3200 601 9400 1132

200 73.3 3300 613 9600 1148

225 80 3400 625 9800 1162.7

250 85.7 3500 635.7 10000 1173.3

275 91.7 3600 645 10500 1210

300 98 3700 655.7 11000 1240

325 104.3 3800 666.3 11500 1266.7

350 110.3 3900 677 12000 1300

375 116 4000 687 12500 1340

400 122 4100 696.3 13000 1380

425 127.3 4200 706 13500 1410

450 132 4300 715.7 14000 1450

475 137.3 4400 725.7 14500 1483.3

500 143 4500 735 15000 1520

550 155 4600 742.3 15500 1553.3

600 166 4700 751.7 16000 1586.7

650 177.3 4800 760 16500 1620

700 188 4900 769 17000 1653.3

750 199 5000 777 17500 1686.7

800 210.7 5100 786 18000 1720

142

Proof load test

Proof load test for HHP anchors (SI units)

anchor proof anchor proof anchor proof

weight load weight load weight load

kg kN kg kN kg kN

850 221.3 5200 797.3 18500 1753.3

900 231 5300 808.7 19000 1780

950 241.7 5400 818 19500 1800

1000 252.3 5500 827.3 20000 1833.3

1050 262 5600 836.3 21000 1900

1100 272.7 5700 845 22000 1956.7

1150 282.7 5800 855.7 23000 2016.7

1200 292 5900 866.3 24000 2070

1250 302 6000 877 25000 2130

1300 311.7 6100 887 26000 2190

1350 321 6200 897.3 27000 2250

1400 330.3 6300 908 28000 2303.3

1450 339.7 6400 917.3 29000 2356.7

1500 349 6500 926.7 30000 2410

1600 366.7 6600 936 31000 2463.3

1700 384 6700 944.7 32000 2516.7

1800 401 6800 953 34000 2623.3

1900 418.3 6900 961 36000 2730

143

Dimensions vryhof tensioners

Main dimensions Stevtensioner dimensions in m. weight in t

Stevtensioner model LBHweight

VA220 2.6 1.0 1.2 5

VA500 5.4 2.4 2.6 20

144

Dimensions vryhof tensioners

Main dimensions Stevtensioner dimensions in m. weight in t

Stevtensioner model LBHweight

VA600 2.2 0.6 0.9 2.5

VA1000 3.1 0.8 1.2 6

VA1250 3.5 0.9 1.4 9

145

Proof load/break

Proof load/break load of chains (in US units)

diameter Proof load Break load Weight

R4-RQ4R3SR3RQ3-API R4-RQ4R3SR3RQ3-API

stud studless stud studless stud stud stud and studlless stud studless

studless studless

inches kips kips kips kips kips kips kips kips kips kips lbs/ft lbs/ft

3/475 66 62 60 54 49 95 86 77 73 55

13/16 88 77 73 71 63 57 111 101 90 86 66

1 131 116 110 106 95 85 167 152 136 128 10 9

11/8165 146 138 133 119 107 210 191 171 162 12 11

11/4203 179 169 163 147 132 257 234 210 198 15 14

13/8244 216 203 197 176 158 310 281 252 238 18 16

11/2289 255 241 233 208 187 366 333 298 282 21 20

15/8337 298 281 271 243 218 427 388 348 329 25 23

13/4388 343 323 313 280 252 492 447 401 379 29 27

17/8443 391 369 357 320 287 562 510 457 432 33 31

2 500 443 417 403 361 324 635 577 517 489 38 35

21/16 531 469 442 427 383 344 673 612 548 518 40 37

21/8561 496 468 452 405 364 712 647 580 548 43 39

23/16 593 524 494 478 428 384 752 684 612 579 45 42

21/4625 553 521 504 452 405 793 721 646 611 48 44

25/16 658 582 549 530 476 427 835 759 680 643 51 46

23/8692 612 577 558 500 449 878 798 715 676 54 49

21/2762 674 635 614 550 494 967 878 787 744 59 54

25/8835 738 696 672 603 541 1059 962 862 815 65 60

211/16 872 771 727 702 630 565 1106 1005 900 852 69 63

23/4910 805 758 733 657 590 1154 1049 940 889 72 66

27/8988 874 823 796 714 640 1253 1139 1020 965 79 72

3 1069 945 891 861 772 693 1356 1232 1103 1044 86 78

31/16 1110 982 925 894 802 719 1408 1280 1146 1084 89 81

31/81152 1019 960 928 832 747 1461 1328 1189 1125 93 85

33/16 1194 1056 995 962 863 774 1515 1377 1233 1167 97 88

31/41237 1094 1031 997 894 802 1570 1427 1278 1209 100 92

35/16 1281 1133 1068 1032 925 830 1625 1477 1323 1251 104 95

33/81325 1172 1105 1068 957 859 1681 1528 1368 1295 108 99

31/21416 1252 1180 1140 1022 918 1796 1632 1462 1383 116 106

39/16 1462 1292 1218 1177 1056 947 1854 1685 1509 1428 121 110

35/81508 1334 1257 1215 1089 977 1913 1739 1557 1473 125 114

33/41603 1417 1336 1291 1158 1039 2033 1848 1655 1566 134 122

313/16 1651 1460 1376 1330 1192 1070 2094 1903 1704 1613 138 126

37/81699 1503 1416 1369 1227 1101 2156 1959 1754 1660 143 130

315/16 1749 1546 1457 1409 1263 1133 2218 2016 1805 1708 147 135

4 1798 1590 1498 1448 1299 1165 2281 2073 1856 1756 152 139

41/81899 1679 1582 1529 1371 1231 2409 2189 1960 1855 162 148

41/42001 1770 1668 1612 1445 1297 2538 2307 2066 1955 172 157

146

Proof load/break

Proof load/break load of chains (in US units)

diameter Proof load Break load Weight

R4-RQ4R3SR3RQ3-API R4-RQ4R3SR3RQ3-API

stud studless stud studless stud stud stud and studlless stud studless

studless studless

inches kips kips kips kips kips kips kips kips kips kips lbs/ft lbs/ft

43/82105 1862 1754 1696 1521 1365 2671 2427 2174 2057 182 166

41/22211 1955 1843 1781 1597 1433 2805 2549 2283 2160 192 176

45/82319 2050 1932 1868 1675 1503 2941 2673 2394 2265 203 186

43/42428 2147 2023 1956 1753 1574 3080 2799 2507 2372 214 196

47/82538 2245 2115 2045 1833 1645 3220 2926 2621 2480 226 206

5 2650 2344 2209 2135 1914 1718 3362 3055 2736 2589 238 217

51/82764 2444 2303 2226 1996 1791 3506 3186 2853 2700 250 228

51/42878 2545 2398 2319 2079 1865 3651 3318 2971 2812 262 239

53/82994 2647 2495 2412 2162 1940 3798 3451 3091 2925 274 251

51/23111 2751 2592 2506 2247 2016 3946 3586 3211 3039 287 262

55/83228 2855 2690 2601 2332 2093 4095 3722 3333 3154 301 275

53/43347 2960 2789 2696 2417 2170 4246 3859 3456 3270 314 287

57/83467 3066 2889 2793 2504 2247 4398 3997 3579 3387 328 299

6 3587 3172 2989 2890 2591 2325 4551 4135 3704 3504 342 312

61/83709 3279 3090 2987 2678 2404 4704 4275 3829 3623 356 325

61/43830 3387 3192 3086 2766 2483 4859 4416 3954 3742 371 339

63/83953 3495 3294 3184 2855 2562 5014 4557 4081 3861 386 353

61/24076 3604 3396 3283 2944 2642 5170 4698 4208 3981 401 367

65/84199 3713 3499 3383 3033 2722 5327 4841 4335 4102 417 381

63/44323 3822 3602 3482 3122 2802 5483 4983 4463 4223 433 395

67/84447 3932 3706 3582 3211 2882 5641 5126 4591 4344 449 410

7 4571 4042 3809 3682 3301 2963 5798 5269 4719 4465 466 425

71/84695 4152 3913 3782 3391 3043 5956 5412 4847 4586 482 440

71/44820 4262 4016 3882 3481 3124 6114 5556 4976 4708 500 456

147

Proof load/break

Proof load/break load of chains (in SI units)

diameter Proof load Break load Weight

R4-RQ4R3SR3RQ3-API R4-RQ4R3SR3RQ3-API

stud studless stud studless stud- stud- stud and studlless stud studless

studless studless

mm kN kN kN kN kN kN kN kN kN kN kg/m kg/m

19 331 293 276 267 239 215 420 382 342 324 87

20.5 385 340 320 310 278 249 488 443 397 376 98

22 442 390 368 356 319 286 560 509 456 431 11 10

24 524 463 436 422 378 339 664 604 541 511 13 12

26 612 541 510 493 442 397 776 706 632 598 15 14

28 707 625 589 570 511 458 897 815 730 691 17 16

30 809 715 674 651 584 524 1026 932 835 790 20 18

32 917 811 764 738 662 594 1163 1057 946 895 22 20

34 1031 911 859 830 744 668 1308 1188 1064 1007 25 23

36 1151 1018 959 927 831 746 1460 1327 1188 1124 28 26

38 1278 1130 1065 1029 923 828 1621 1473 1319 1248 32 29

40 1410 1247 1175 1136 1018 914 1789 1625 1456 1377 35 32

42 1548 1369 1290 1247 1118 1004 1964 1785 1599 1513 39 35

44 1693 1497 1411 1364 1223 1097 2147 1951 1748 1654 42 39

46 1843 1630 1536 1485 1331 1194 2338 2124 1903 1800 46 42

48 1999 1767 1666 1610 1443 1295 2535 2304 2063 1952 50 46

50 2160 1910 1800 1740 1560 1400 2740 2490 2230 2110 55 50

52 2327 2058 1939 1874 1681 1508 2952 2682 2402 2273 59 54

54 2499 2210 2083 2013 1805 1620 3170 2881 2580 2441 64 58

56 2677 2367 2231 2156 1933 1735 3396 3086 2764 2615 69 63

58 2860 2529 2383 2304 2066 1854 3628 3297 2953 2794 74 67

60 3048 2695 2540 2455 2201 1976 3867 3514 3147 2978 79 72

62 3242 2866 2701 2611 2341 2101 4112 3737 3347 3166 84 77

64 3440 3042 2867 2771 2484 2230 4364 3965 3551 3360 90 82

66 3643 3221 3036 2935 2631 2361 4621 4200 3761 3559 95 87

68 3851 3406 3209 3102 2782 2496 4885 4440 3976 3762 101 92

70 4064 3594 3387 3274 2935 2634 5156 4685 4196 3970 107 98

73 4392 3884 3660 3538 3172 2847 5572 5064 4535 4291 117 107

76 4731 4183 3942 3811 3417 3066 6001 5454 4884 4621 126 116

78 4962 4388 4135 3997 3584 3216 6295 5720 5123 4847 133 122

81 5317 4702 4431 4283 3840 3446 6745 6130 5490 5194 144 131

84 5682 5024 4735 4577 4104 3683 7208 6550 5866 5550 155 141

87 6056 5355 5046 4878 4374 3925 7682 6981 6252 5916 166 151

90 6439 5693 5365 5187 4650 4173 8167 7422 6647 6289 177 162

92 6699 5923 5582 5396 4838 4342 8497 7722 6916 6544 185 169

95 7096 6275 5913 5716 5125 4599 9001 8180 7326 6932 198 181

97 7365 6513 6138 5933 5319 4774 9343 8490 7604 7195 206 188

100 7776 6876 6480 6264 5616 5040 9864 8964 8028 7596 219 200

102 8054 7122 6712 6488 5817 5220 10217 9285 8315 7868 228 208

148

Proof load/break

Proof load/break load of chains (in SI units)

diameter Proof load Break load Weight

R4-RQ4R3SR3RQ3-API R4-RQ4R3SR3RQ3-API

stud studless stud studless stud- stud- stud and studlless stud studless

studless studless

mm kN kN kN kN kN kN kN kN kN kN kg/m kg/m

105 8478 7497 7065 6829 6123 5495 10754 9773 8753 8282 241 221

107 8764 7750 7304 7060 6330 5681 11118 10103 9048 8561 251 229

111 9347 8265 7789 7529 6750 6058 11856 10775 9650 9130 270 246

114 9791 8658 8159 7887 7071 6346 12420 11287 10109 9565 285 260

117 10242 9057 8535 8251 7397 6639 12993 11807 10574 10005 300 274

120 10700 9461 8916 8619 7728 6935 13573 12334 11047 10452 315 288

122 11008 9734 9173 8868 7950 7135 13964 12690 11365 10753 326 298

124 11319 10009 9432 9118 8175 7336 14358 13048 11686 11057 337 308

127 11789 10425 9824 9497 8515 7641 14955 13591 12171 11516 353 323

130 12265 10846 10221 9880 8858 7950 15559 14139 12663 11981 370 338

132 12585 11129 10488 10138 9089 8157 15965 14508 12993 12294 382 348

137 13395 11844 11162 10790 9674 8682 16992 15441 13829 13085 411 375

142 14216 12571 11847 11452 10267 9214 18033 16388 14677 13887 442 403

147 15048 13306 12540 12122 10868 9753 19089 17347 15536 14700 473 432

152 15890 14051 13241 12800 11476 10299 20156 18317 16405 15522 506 462

157 16739 14802 13949 13484 12089 10850 21234 19297 17282 16352 540 493

162 17596 15559 14663 14174 12708 11405 22320 20284 18166 17188 575 525

165 18112 16016 15094 14590 13081 11739 22976 20879 18699 17693 596 545

168 18631 16474 15525 15008 13455 12075 23633 21477 19234 18199 618 564

171 19150 16934 15959 15427 13831 12412 24292 22076 19771 18707 640 585

175 19845 17548 16538 15986 14333 12863 25174 22877 20488 19386 671 613

178 20367 18010 16972 16407 14709 13201 25836 23479 21027 19896 694 634

180 20715 18318 17263 16687 14961 13427 26278 23880 21387 20236 710 648

185 21586 19088 17989 17389 15590 13991 27383 24884 22286 21087 750 685

149

Chain components

Chain components and forerunners

3.6D

4.4D

3.96D

1.1D

1.2D

4.35D

F C B H B A E A A A

PL A A A A A A A A A

A B H B A E A A A

K C B A E A A A A A

K C B H B A E A A A

F C B A E A A A A A

VA-01

VA-02

VA-03

150

Chain components

Chain components and forerunners

C B H B A E A A A

A A A A A A A A A

PL A B H B A E A A A

K C B A E A A A A A

K C B H B A E A A A

C B A E A A A A A

VA-04

VA-05

VA-06

4.2D

1.52D

95 mm

390 mm

650 mm

151

Chain components

3.8D

4.7D

9.7D

6.3D

1.2D

1.3D 2.8D

1.2D

1.6D

7.1D

1.4D

0.8D3.4D

3.1D

5.2D

1.4D

1.8D

8.7D

2.4D

4.6D 1.8D

1.4D

Chain components and forerunners

3.3D

1.45D 4D

13.2D

4.15D

2.2D

1.7D 2.2D 1.65D 1.35D

5.15D

A= common link

B= enlarged link

C= end link

E= joining shackle kenter type

F= anchor shackle Dtype

G= joining shackle Dtype

PL = pear link

H= swivel

I= swivel shackle

K= special end link

152

Connecting links

ED A

Pear shaped anchor connecting link (pearlink) dimensions in mm

NO chain size ABCDEFGHJKkg

4 32 - 40 298 206 59 40 48 83 44x44 56 26 43 13

5 42 - 51 378 260 76 51 64 100 51x 60 74 32 52 27

6 52 - 60 454 313 92 60 76 121 62x 73 88 37 64 49

7 62 - 79 562 376 117 79 95 149 85x79 111 48 76 94

8 81 - 92 654 419 133 92 124 149 111x102 130x133 54 79 149

9 94 - 95 692 435 146 98 130 159 124x137 141 57 83 236

10 97 - 102 889 571 190 121 165 190 130 181 73 108 386

11 103 - 108 940 610 203 127 175 203 156 200 76 111 418

153

Connecting links

Detachable chain connecting link (C-connector) dimensions in mm

chain size AB CDE FGweight kg

30 - 32 190.5 127 44 32 35 39 21 4.5

33 - 35 210 140 49 35 39 42 23 6.0

36 - 38 229 152 53 38 43 46 25 7.8

40 - 42 248 165 57 41 50 50 27 10.0

43 - 44 267 190 62 44 51 56 30 12.5

46 - 48 286 184 64 48 55 60 31 14.5

50 - 51 305 197 64 51 59 64 33 16.5

52 - 54 324 210 67 54 64 67 36 20.0

56 - 58 343 221 71 57 67 71 38 23.5

59 - 60 362 234 78 60 70 75 40 27.5

62 - 64 381 246 79 64 73 78 42 32.0

66 - 67 400 246 83 67 78 79 44 37.0

68 - 70 419 275 92 73 83 90 46 45.5

71 - 73 438 283 94 73 85 93 48 48.5

74 - 76 457 295 95 76 90 94 50 54.5

78 - 79 476 308 102 79 92 96 52 62.5

81 - 83 495 320 103 83 92 103 55 73.0

84 - 86 514 332 107 86 100 107 57 80.5

87 - 89 537 350 116 92 105 114 59 93.5

90 - 92 552 356 119 92 106 116 61 97.5

94 - 95 571 368 122 95 114 119 62 116.0

97 - 98 590 381 127 98 117 121 67 123.0

100 - 102 607 394 132 102 119 122 68 130.0

154

Conversion table

to convert from multiply by to obtain

length millimetres mm 0.03937 inches in

metres m 3.28084 feet ft

kilometres km 0.62137 miles mi

kilometres km 0.53996 nautical miles nmile

inches in 25.4 millimetres mm

feet ft 0.30480 metres m

miles mi 1.60934 kilometres km

nautical miles nmile 1.852 kilometres km

area square millimetres mm20.00155 square inches in2

square metres m210.76391 square feet ft2

square kilometres km20.38610 square miles mi2

square inches in2645.16 square millimetres mm2

square feet ft20.09290 square metres m2

square miles mi22.58999 square kilometres km2

volume millilitres ml 0.06102 cubic inches in3

litres l 0.26417 gallons (US) gal

cubic metres m335.31467 cubic feet ft3

cubic inches in316.38706 millilitres ml

gallons (US) gal 3.78541 litres l

cubic feet ft30.02832 cubic metres m3

mass kilograms kg 2.20462 pounds lb

metric tons t 1.10231 short tons US ton

pounds lb 0.45359 kilograms kg

short tons US ton 0.90718 metric tons t

density kilograms per cubic metre kg/m30.06243 pounds per cubic foot lb/ft3

pounds per cubic foot lb/ft316.01846 kilograms per cubic metre kg/m3

155

Conversion table

to convert from multiply by to obtain

force or weight kilonewtons kN 0.22481 kips kip

kilonewtons kN 0.10197 metric tons t

metric tons t 2.20462 kips kip

kips kip 4.44822 kilonewtons kN

metric tons t 9.80665 kilonewtons kN

kips kip 0.45359 metric tons t

pressure or stress kilopascals kPa 20.88555 pounds per square foot psf

megapascals MPa 0.14504 kips per square inch ksi

pounds per square foot psf 0.04788 kilopascals kPa

kips per square inch ksi 6.89472 megapascals MPa

velocity metres per second m/s 1.94384 knots kn

metres per second m/s 2.23694 miles per hour mph

knots kn 0.51444 metres per second m/s

miles per hour mph 0.44704 metres per second m/s

temperature degrees celsius ˚C multiply by 1.8 then add 32 degrees fahrenheit ˚F

degrees fahrenheit ˚F subtract 32 then multiply by 0.555 degrees celsius ˚C

156

Mooring line catenary

When the mooring line of a floater is deployed, part of the mooring line

will lay on the seabed and part of the mooring line will be suspended in the

water. The part of the mooring line that is suspended in the water will take

on a catenary shape. Depending on the waterdepth, the weight of the

mooring line and the force applied to the mooring line at the fairlead, the

length of the suspended mooring line (S in [m]) can be calculated with:

with d : the waterdepth plus the distance between sealevel and the

fairlead in [m]

F:the force applied to the mooring line at the fairlead in [t]

and w : the unit weight of the mooring line in water in [t/m]

The horizontal distance (X in [m]) between the fairlead and the touchdown

point of the mooring line on the seabed can be calculated with:

The weight of the suspended chain (V in [t]) is given by:

V = w x S

See fig. 4-01 for a clarification of the symbols used. The angle is the angle

between the mooring line at the fairlead and the horizontal.

fig. 4-01

0 100 200 300 400 500

1600



1200



800



400



depth in meters

length S and X in meters



S, F = 50 t

S, F = 100 t

X, F = 150 t

S, F = 100 t

S, F = 300 t

X, F = 200 t

S, F = 150 t

X, F = 50 t

X, F = 250 t

S, F = 200 t

X, F = 100 t

X, F = 300 t

fig. 4-02

S = √d x

{

2 x F -d

}

S+F

X =

{

F-d

}

xelog w

wF-d

{}

157

Mooring line catenary

Example

In fig. 4-02, the suspended length S and the horizontal distance X are plot-

ted for a 76 mm chain for different loads F (ranging from 50 t to 300 t). The

suspended weight of the mooring line is plotted in fig. 4-03. The submerged

unit weight of the 76 mm chain is 0.110 t/m.

0 100 200 300 400 500

180



140



100



60



20

depth in meters

weight catenary chain in t



F = 50 t

F = 250 t

F = 100 t

F = 300 t

F = 150 t F = 200 t

fig. 4-03

158

Mooring line holding capacity

Mooring line holding capacity on the seabed

The holding capacity (P) in [t] of the part of the mooring line that is laying

on the seabed, can be estimated with the following equation:

P = f x l x w

with

f:friction coefficient between the mooring line and the seabed

l:the length of the mooring line laying on the seabed in [m]

w:the unit weight of the mooring line in water in [t/m]

If no detailed information on the friction coefficient is available, the

following values can be used:

The values for the friction coefficient given under starting can be used to

calculate the holding capacity of the mooring line, while the values given

under sliding can be used to calculate the forces during deployment of the

mooring line.

friction coefficient

mooring line type starting sliding

chain 1.0 0.7

wire rope 0.6 0.25

159

Shackles

Chain shackle Anchor shackle

160

Shackles

Chain shackle and anchor shackle

According to U.S. federal specification (RR-C-271) dimensions in mm

SWL t ABCDDEOWeight Weight

chain anchor anchor Chain anchor

shackle shackle shackle shackle KG shackle KG

2 13 16 22 43 51 32 32 0.38 0.44

3.25 16 19 27 51 64 38 43 0.66 0.79

4.75 19 22 31 59 76 44 51 1.05 1.26

6.5 22 25 36 73 83 50 58 1.46 1.88

8.5 25 28 43 85 95 56 68 2.59 2.79

9.5 28 32 47 90 108 64 75 3.34 3.8

12 32 35 51 94 115 70 83 4.74 5.26

13.5 35 38 57 115 133 76 92 6.19 7

17 38 42 60 127 146 84 99 7.6 8.8

25 45 50 74 149 178 100 126 12.82 15

35 50 57 83 171 197 114 138 18.16 20.65

42.5 57 65 95 190 222 130 160 27.8 29.3

55 65 70 105 203 254 140 180 35.1 41

85 75 80 127 230 330 160 190 60 62.3

120 89 95 146 267 381 190 238 93 109.5

150 102 108 165 400 400 216 275 145 160

200 120 130 175 500 500 260 290 180 235

250 125 140 200 540 540 280 305 225 285

300 135 150 200 600 600 300 305 305 340

400 165 175 225 650 650 350 325 540 570

500 175 185 250 700 700 370 350 580 685

600 195 205 275 700 700 410 375 850 880

700 205 215 300 730 730 430 400 920 980

800 210 220 300 730 730 440 400 990 1110

900 220 230 320 750 750 460 420 1165 1295

1000 230 240 340 750 750 480 420 1315 1475

1200 250 280 400 840 840 560 500 1700 1900

1500 260 325 460 840 870 650 600 2500 2800

161

Shackles

Heavy duty shackle double nut dimensions in mm

SWL t rope dia ABCDEFGweight

inch kg

60 12-13” 65 76 175 350 165 305 535.5 65

85 14-15” 80 90 220 390 178 380 604 87

110 16-18” 90 102 254 430 210 434 676 146

130 19-21” 100 114 280 480 235 480 754.5 194

175 22-23” 125 133 300 600 265 550 924 354

225 24”-> 130 146 333 720 305 593 1075.5 410

162

Shackles

Sling shackle dimensions in mm

SWL t ABCDE Fweight kg

75 70 70 105 290 186 120 67

125 85 80 130 365 220 150 110

150 89 95 140 390 250 170 160

200 100 105 150 480 276 205 220

250 110 120 170 540 300 240 320

300 122 134 185 600 350 265 350

400 145 160 220 575 370 320 635

500 160 180 250 630 450 340 803

600 170 200 275 700 490 370 980

700 190 215 300 735 540 400 1260

800 200 230 325 750 554 420 1430

900 220 255 350 755 584 440 1650

1000 240 270 380 760 614 460 2120

1250 260 300 430 930 644 530 2400

1500 280 320 460 950 680 560 2980

CAA

163

Wire rope

Depending on the required service life of the mooring system, the following types of wire rope

are recommended:

Design life recommended product type

Up to 6 years Six strand

Up to 8 years Six strand c/w zinc anodes

Up to 10 years Six strand c/w ‘A’ galvanised outer wires & zinc anodes

10 years plus Spiral strand

15 years plus Spiral strand c/w Galfan coated outer wires

20 years plus Spiral strand c/w HDPE sheathing

The two rope constructions have differing properties. The advantages of each of the rope types

are presented in the following table:

Spiral strand six strand

Higher strength/weight ratio Higher elasticity

Higher strength/diameter ratio Greater flexibility

Torsionally balanced Lower axial stiffness

Higher corrosion resistance

Properties of spiral stand wire rope

Nominal MBL Axial Stiffness Nominal Weight in kg/m Submerged Nominal Sheathing

Diameter kN MN Unsheathed Sheathed nominal weight Steel Area Thickness

mm (inch) kg/m mm2mm

76 (3) 5647 557 28.4 30.4 23.8 3377 8

82 (3.25) 6550 627 33.0 35.1 27.5 3917 8

90 (3.5) 7938 760 39.9 42.9 33.4 4747 10

95.5 (3.75) 8930 855 44.9 48.1 37.5 5341 10

102 (4) 10266 982 51.6 55.3 43.1 6139 11

108 (4.25) 11427 1093 57.5 61.3 48.0 6834 11

114 (4.5) 12775 1222 64.2 68.3 53.6 7640 11

121.5 (4.75) 14362 1353 72.2 76.5 59.7 8589 11

127 (5) 15722 1481 79.1 83.6 66.0 9403 11

133 (5.25) 17171 1599 86.8 91.5 72.4 10314 11

141 (5.5) 19180 1799 97.5 102.4 81.5 11609 11

146.5 (5.75) 20469 1940 105.1 110.2 87.7 12515 11

153 (6) 22070 2110 114.5 119.7 95.5 13616 11

164

Wire rope

Higher fatigue resistance

Properties of six strand wire rope

Diameter MBL Axial Stiffness Rope weight Submerged Torque

mm (inch) kN MN kg/m rope weight Factor

kg/m Nm/kN

64 2.5 3360 189.4 17.3 15.3 4.7

71 2.75 3990 233.0 20.8 18.3 5.2

77 3 4767 278.8 25.7 22.7 5.8

83 3.25 5399 319.7 29.5 26.0 6.3

89 3.50 6414 415.2 35.0 30.9 6.9

96 3.75 6965 483.8 40.5 35.7 7.5

102 4 7799 573.5 44.5 39.3 8.1

108 4.25 8240 642.1 49.8 43.9 8.6

114 4.50 9172 707.0 55.3 48.8 9.1

121 4.75 10055 775.7 60.6 53.5 9.7

127 5 11134 866.6 67.7 59.8 10.2

133 5.25 11728 912.9 73.8 65.5 10.6

140 5.50 12925 1006.1 80.9 71.7 11.2

Note: MBL based on 10 years design life.

Torque factor presented in the last column is an approximate value at 20% applied load.

165

Wire rope

Installation of sheathed spiral strand

The limiting factors for the installation of a sheathed spiral strand are

defined by the properties of the sheathing. The maximum bearing pressure

(σb) on the sheath is limited to 21 N/mm2to avoid permanent deformation.

The minimum bending diameter permitted can be calculated using the fol-

lowing formula:

D = (4 x W) / (πx σbx {d x 0.15 x t}0.5)

Where :

D=sheave diameter mm

W=line load N

d=sheathed cable diameter mm

t=sheathing radial thickness mm

σb= maximum bearing pressure N/mm2

The above formula ensures no damage to the sheathing through bending.

In addition to prevent damage to the cable within the sheathing, the mini-

mum bending diameter is 24 times the unsheathed cable diameter., i.e. D >

24 x (d – 2 x t).

166

Wire rope sockets

Closed spelter socket dimensions in mm

NO MBL t for wire ABD1 FGX

dia. mm

428 650 75 - 84 360 375 150 350 150 1110

430 820 85 - 94 400 410 175 380 170 1250

431 1000 95 - 104 425 450 205 400 200 1400

433 1200 105 - 114 500 500 230 500 210 1570

440 1500 115 - 130 580 570 260 600 225 1800

445 1700 131 - 144 625 630 300 680 240 1940

450 1900 145 - 160 700 700 325 725 275 2150

167

Wire rope sockets

Closed spelter socket dimensions in mm

NO MBL Rope diameter ABCD EFGWeight

tons mm inch kg

201 45 20 - 22 7/8101 90 33 24 47 92 38 4

204 70 23 - 26 1 114 103 36 28 57 104 44 6.5

207 100 27 - 30 1 1/8127 116 39 32 63 114 51 7.5

212 125 31 - 36 1 1/4- 1 3/8139 130 43 38 70 127 57 11

215 150 37 - 39 1 1/2152 155 51 41 79 136 63 13

217 200 40 - 42 1 5/8165 171 54 44 82 146 70 17

219 260 43 - 48 1 3/4- 1 7/8190 198 55 51 89 171 76 24

222 280 49 - 51 2 - 2 1/8216 224 62 57 96 193 82 36.5

224 360 55 - 60 2 1/4- 2 3/8228 247 73 63 108 216 92 50

226 450 61 - 68 2 1/2- 2 5/8248 270 79 73 140 241 102 65

227 480 69 - 75 2 3/4- 2 7/8279 286 79 79 159 273 124 93

228 520 76 - 80 3 - 3 1/8305 298 83 86 171 292 133 110

229 600 81 - 86 3 1/4- 3 3/8330 311 102 92 184 311 146 142

230 700 87 - 93 3 1/2- 3 5/8356 330 102 99 197 330 159 170

231 875 94 - 102 3 3/4- 4 0/0381 356 108 108 216 362 178 225

233 1100 108 - 115 4 1/2450 425 120 125 235 405 190 340

240 1250 122 - 130 5 500 475 120 138 260 515 210 -

250 1400 140 - 155 5 1/2- 6 0/0580 550 150 160 300 510 250 -

260 1600 158 - 167 6 1/2675 600 175 175 325 600 300 -

168

Wire rope sockets

Open spelter socket dimensions in mm

NO MBL t for wire ABCD1 JX

dia. mm

338 650 75 - 84 375 298 296 140 159 1050

340 820 85 - 94 410 320 340 152 171 1170

344 1000 95 - 104 425 343 362 178 191 1300

346 1200 105 - 114 500 500 440 200 200 1570

350 1500 115 - 130 580 580 580 250 220 1800

370 1700 131 - 144 625 625 625 280 230 1940

380 1900 145 - 160 700 700 680 300 250 2150

169

Wire rope sockets

JK CK

Open spelter socket dimensions in mm

NO MBL Rope diameter ABCDD1 JKWeight

tons mm inch kg

100 32 17 - 19 3/489 76 80 21 35 38 16 3.2

104 45 20 - 22 7/8101 89 90 24 41 44 19 4.7

108 70 23 - 26 1 114 101 120 28 51 51 22 7.5

111 100 27 - 30 1 1/8127 114 130 32 57 57 25 11.6

115 125 31 - 36 1 1/4-1 3/8139 127 144 38 63 63 28 16.8

118 150 37 - 39 1 1/2152 162 160 41 70 76 30 24

120 200 40 - 42 1 5/8165 165 176 44 76 76 33 27.5

125 260 43 - 48 1 3/4- 1 7/8190 178 200 51 89 89 39 40.5

128 280 49 - 54 2 - 2 1/8216 228 216 57 95 101 46 60.5

130 360 55 - 60 2 1/4- 2 3/8228 250 236 63 108 113 53 90

132 450 61 - 68 2 1/2- 2 5/8248 273 264 73 121 127 60 122

135 480 69 - 75 2 3/4- 2 7/8279 279 276 79 127 133 73 157

138 520 76 - 80 3 - 3 1/8305 286 284 86 133 146 76 195

140 600 81 - 86 3 1/4- 3 3/8330 298 296 92 140 159 79 221

142 700 87 - 93 3 1/2- 3 5/8356 318 340 99 152 171 83 281

144 875 94 - 102 3 3/4- 4 0/0381 343 362 108 178 191 89 397

146 1100 108 - 115 4 1/2460 480 440 125 190 208 101 570

150 1250 122 - 130 5 500 500 560 138 250 210 120 980

160 1400 140 - 155 5 1/2- 60/0580 500 600 160 275 230 140 -

170 1600 158 - 167 6 1/2675 600 650 175 290 230 175 -

170

Wire rope sockets

CR-socket dimensions in mm

NO MBL t rope dia AB C DE Fweight

mm kg

522 250 49 - 54 215 125 55 57 115 200 30

524 300 55 - 60 230 145 65 63 135 230 46

526 400 61 - 68 250 160 75 73 150 270 62

527 500 69 - 75 280 175 80 79 165 300 87

528 600 76 - 80 310 190 85 86 175 325 110

529 700 81 - 86 340 205 100 92 200 350 135

530 800 87 - 93 360 220 105 99 205 360 160

531 900 94 - 102 380 240 110 108 225 380 208

533 1000 108 - 115 450 260 125 120 240 420 270

Advantages of the CR socket

•Guaranteed high breaking load.

•Integrated non rotating stopper system which prevents the tamp from turning

or slipping out of the cone.

•An open-widow side for easy rope handling.

•A high performance connection for the right combination with a detach-

able link.

•No rings in the cone to a give a maximum rope/socket connection.

•Impact value of min. 27 Joule at -40˚C.

171

Wire rope sockets

Forged eye socket

Dimension Size

A 1.7 D

B According to insulating tube thickness

C 1.4 D

X According to wire rope diameter

Y According to wire rope diameter

Note : D is the nominal diameter of the chain

that connects to the socket.

172

Thimbles

Main dimensions bellmouth thimble dimensions in mm

For wire dia. AB CDE F Kweight kg

10”-12” 366 606 277 480 195 166 85 80

15”-16” 440 746 352 608 248 191 105 125

18”-21” 454 844 352 660 300 226 118 175

173

Thimbles

Main dimensions tubular thimble dimensions in mm

For ABCDEFGH1 H2 X weight

wire dia. kg

12” 521 420 260 194 144 130 20 130 140 10 50

15” 625 510 312 194 144 150 25 158 168 40 80

18” 727 610 368 219 169 175 30 183 194 40 140

21” 829 740 415 219 169 200 30 206 219 40 180

24” 930 880 465 273 201 225 30 229 245 40 260

27” 1035 1020 517 273 201 250 30 260 273 40 380

174

Synthetic ropes

Production and construction in accordance with recognized standards.

The properties of various rope sizes are presented in the following tables.

Rope properties

Polyester Dyneema

Material Polyester High Modulus PolyEthylene

Construction Parallel strand construction Parallel strand construction

Protective cover Polyester Composite yarn

Color of rope White with marker yarns White

Specific gravity 1.38 - sinks 0.975 - floating

Melting point 251° C 145° C

Abrasion resistance Excellent Excellent

UV resistance Excellent Good

Temperature resistance Workable at sub-zero temperatures Medium

Chemical resistance Good Excellent

Water absorption/fibers < 0.5% < 0.05%

Water uptake + / - 30% n.a

Dry & weight conditions Wet strength equals to dry strength Wet strength equals to dry strength

175

Synthetic ropes

HMPE

Diameter MBL Weight stiffness

mm k/N kg/m EA

k/N

81 3649 3.30 2.03e+ 05

93 5108 4.34 2.84e+ 05

108 7298 5.85 4.05e+ 05

117 8757 6.83 4.87e+ 05

129 10946 8.28 6.08e+ 05

137 12406 9.24 6.89e+ 05

147 14595 10.7 8.11e+ 05

154 16055 11.6 8.92e+ 05

163 18244 13.0 1.01e+ 05

169 19703 13.9 1.09e+ 05

177 21893 15.3 1.22e+ 05

182 23352 16.3 1.30e+ 05

187 24812 17.2 1.38e+ 05

Note : MBL in spliced condition.

Polyester mooring line: strength table

Diameter MBL Total weight kg/m Submerged weight kg/m Stiffness kN

mm k/N @2% MBL @20% MBL @2% MBL @20% MBL EA1EA2EA3

113 3723 8.8 8.2 2.1 1.9 7.19e+ 04 8.43e+ 04 1.10e+ 04

137 5754 12.9 12.0 3.1 2.9 1.18e+ 05 1.38e+ 05 1.80e+ 05

154 7446 16.2 15.1 3.9 3.6 1.57e+ 05 1.84e+ 05 2.40e+ 05

169 9138 19.5 18.2 4.7 4.4 1.96e+ 05 2.30e+ 05 2.99e+ 05

183 10830 22.8 21.2 5.5 5.1 2.35e+ 05 2.76e+ 05 3.59e+ 05

195 12522 26.0 24.2 6.2 5.8 2.74e+ 05 2.22e+ 05 4.19e+ 05

207 14215 29.2 27.2 7.0 6.5 3.14e+ 05 3.68e+ 05 4.79e+ 05

227 17261 35.0 32.6 8.4 7.8 3.53e+ 05 4.14e+ 05 5.39e+ 05

245 20307 40.7 37.9 9.7 9.1 3.27e+ 05 3.83e+ 05 4.99e+ 05

Note : Minimum Breaking Load (MBL) in spliced condition.

Weights are presented for a rope loaded to 2% and 20% of MBL

1cycling between 10 - 30 % MBL

2cycling between 20 - 30 % MBL

3cycling between 40 - 50 % MBL

176

Synthetic ropes

Recommended practise for handling fibre rope mooring lines

before and during installation

•Ropes should not be permanently installed around bollards or fairleads.

•A minimum bending radius should be observed. The minimum bend

radius (D/d) with very low line tensions should be larger than 6.

•When unreeling the rope, maximum line tension should be observed, to

avoid pulling the rope into the underlying layer.

•Torque or twist in the rope should be avoided.

•Fibre ropes should not be run over surfaces which have sharp edges, grooves,

nicks or other abrasive features.

•Care should be taken when applying shearing forces to the rope.

•There should be no “hot work” such as welding in the vicinity of the rope.

•Frictional heat from excessive slippage of the fibre rope over a capstan,

drum, etc. must be avoided.

•Care should be taken that ropes do not get knotted or tangled.

•Rope contact with sharp gritty materials should be avoided.

•Abrasion or fouling of the mooring line with other anchoring equipment

such as anchor, steel wire rope, chain and connectors must be avoided.

•Chasers should not be used on fibre ropes.

•Shark jaw stoppers designed for use with steel wire rope or chain should not be

used for handling fibre ropes.

•It should be avoided that the ropes undergo more than 1000 loadcycles

with a line tension smaller than 5% of the MBL.

•Pre-deployed lines should not be left buoyed at the surface waiting con-

nection to the platform, unless a minimum line tension of 5% (for poly-

ester) of the MBL is maintained.

•If the fibre rope is laid on the seabed, it must be protected against exter-

nal abrasion and ingress of abrasive particles.

177

Mooring hawsers

Double braided nylon Circular braided nylon Deltaflex 2000

Circ. Diameter Ndbs Nwbs weight Ndbs Nwbs weight Ndbs = weight

inch mm ttkg/m ttkg/m nwbs t kg/m

12 96 208 198 5.7 205 195 5.0 217 5.7

13 104 249 236 6.7 256 244 6.0 258 6.7

14 112 288 273 7.8 307 292 7.3 297 7.8

15 120 327 311 8.9 358 341 8.4 339 8.9

16 128 368 349 10.2 406 387 9.5 378 10.2

17 136 419 398 11.4 454 433 10.7 423 11.5

18 144 470 446 12.8 501 477 12.0 468 12.8

19 152 521 495 14.3 547 521 13.2 523 14.3

20 160 577 548 15.8 597 569 14.4 578 15.9

21 168 635 603 17.4 644 614 15.7 636 16.9

Specific gravity 1.14 1.14 1.14

Melting point 250˚C 215˚C 260˚C

Approximate elongation at Circular braided nylon (double braided Deltaflex 2000

first loading (broken- is similar)

in rope, dry and wet

condition)

At 20% of MBL ± 16% ± 19%

At 50% of MBL ± 22% ± 26%

At break ± >40% ± 33%

Note : ndbs = new dry break strength in spliced condition

nwbs = new wet break strength in spliced condition

Deltaflex 2000 in 8 strand plaited construction.

178

Mooring hawsers

Double braided construction versus circular braided construction

The circular braided construction can be defined as a recent alternative for

the double braided construction. The elongation and TCLL values of both

construction types are the same. The efficiency (breaking load/raw material) of

the circular braided construction is however much higher, which means that

the circular braided construction can be more budgetary attractive.

Both construction types have an overbraided jacket as part of their con-

struction, but the important difference is that where the overbraiding of

the double braided construction is load bearing, the overbraiding of the cir-

cular braided construction is just there for protection. This means that when

the overbraiding is damaged due to chafing or other reasons, the stability

and break load of the circular braided construction will remain unchanged,

while the double braided construction should be considered as structurally

damaged (loss of stability and a lower break load).

Advantages of Deltaflex 2000

When compared to nylon hawsers, a Deltaflex 2000 hawser has the folowing

advantages:

•Equal strength in dry and wet conditions.

•Strength is 10% to 20% higher than wet double braided nylon.

•High energy absorption and elastic recovery.

•No water absorption.

•One of the highest TCLL (thousand cycle load level) values of all synthetic

ropes.

179

Main dimensions chasers

J-Chaser

VA 101

J-Lock Chaser

VA 115

Permanent Wire Chaser

VA 210-213-214-215

Permanent Chain Chaser

VA 102-106-110-112

Detachable Chain Chaser

VA 107-108-111

180

Main dimensions chasers

Main dimensions chasers dimensions in mm

Type AB C DE FGHproofload weight

t kg

VA 101 2483 1829 - 699 305 - 124 86 250 1882

VA 102 1657 1143 991 762 305 191 124 86 250 1088

VA 106 1702 1168 991 762 381 203 130 99 250 1451

VA 107 1886 1143 1080 762 305 191 124 86 250 1238

VA 108 1931 1168 1067 762 381 203 130 99 250 1656

VA 110 1867 1245 1130 838 330 203 130 99 250 1433

VA 111 1994 1245 1130 838 330 203 130 99 250 1742

VA 112 2210 1384 1397 953 356 260 130 99 250 2064

VA 115 2083 1486 - 711 533 305 124 86 250 1778

VA 210 2073 1245 1203 838 432 330 130 99 250 1959

VA 213 1962 1099 1086 692 445 330 130 99 250 1846

VA 214 2318 1308 1397 902 508 330 130 99 250 2530

VA 215 2051 1168 1060 711 445 356 178 127 400 2495

181

Main dimensions chasers

Note: the VA115 is available in two versions: the VA 115/35 for 21/2” to 31/2”

chain and the VA115/45 for 33/4” to 41/2” chain.

Restoration of worn chaser profiles

Worn profiles may be restored by application of a weld deposit. Care must

be taken to ensure a satisfactory bond between parent material and the

weld deposit and to avoid the generation of a brittle structure in the area

of repair.

The following procedure is recommended:

•The area to be welded must be cleaned to a bright metal finish.

•Prior to the commencement of welding, the parent material should be

pre-heated to 180-200 ˚C and the pre-heat temperature is to be maintained

during welding.

•The initial layer of weld deposit should be effected by a high nickel

electrode such as: Metrode C.I. softlow nickel – N.I.O. 8C.2FE A.W.S.

No.A5.15.ENI-CL.

•Subsequent layers of welding may be laid using a less noble electrode

such as: Metrode CI special cast Ni Fe – FE.55.NI-1.3.C A.W.S.

No. A5.15.ENI.FE.CI.

•Each successive layer of weld must be cleaned and hammered.

•On completion of welding, the built-up zone and surrounding area

should be insulation wrapped to permit slow cooling.

182

Stevin Mk3

Stevin Mk3 UHC chart

Stevin Mk3 size in t

typical Ultimate Holding Capacity (UHC) in t

medium clay

very soft clay

sand and hard clay

The Stevin Mk3 design line very soft clay

represents soils such as very soft clays (mud), and

loose and weak silts.

The line is applicable in soil that can be described

by an undrained shear strength of 4 kPa at the

surface increasing by 1.5 kPa per meter depth or in

the equation Su = 4+1.5*z. with Su in kPa and z

being the depth in meters below seabed. In very

soft soils the optimum fluke/shank angle is

typically 50 deg.

The design line sand represents competent soils,

such as medium dense sands and stiff to hard clays

and is based on a silica sand of medium density. In

sand and hard clay the optimal fluke/shank angle

is 32°.

The medium clay design line represents soils

such as silt and firm to stiff clays. The fluke/shank

angle should be set at 32° for optimal performance.

Ultimate Holding Capacity

The prediction lines above

represent the equation UHC=

A*(W)0.92 with UHC as the

Ultimate Holding Capacity in

tonnes and A a parameter

depending on soil, anchor and

anchor line with values between

16 and 31.

183

Stevin Mk3

Stevin Mk3 drag and penetration chart

Example: loading 70% of ultimate holding

capacity corresponds with 48% of maximum

drag and 80% of maximum penetration at

ultimate holding capacity.

drag

penetration

anchor load drag penetration

as % of % max as % max

UHC drag penetration

70 48 80

60 37 68

50 27 55

40 18 42

30 9 23

Stevin Mk3 size in t

penetration in medium clay

penetration in very soft clay

drag in sand

drag in medium clay

drag in very soft clay

penetration in sand

typical drag and penetration in meters

anchor loaded to ultimate holding capacity (UHC)

184

Stevpris Mk5

Stevpris Mk5 UHC chart

Ultimate Holding Capacity

The prediction lines above

represent the equation UHC=

A*(W)0.92 with UHC as the

Ultimate Holding Capacity in

tonnes and A a parameter

depending on soil, anchor and

anchor line with values between

24 and 110.

Stevpris Mk5 size in t

typical Ultimate Holding Capacity (UHC) in t

medium clay

very soft clay

sand and hard clay

The Stevpris Mk5 design line very soft clay

represents soils such as very soft clays (mud), and

loose and weak silts. The line is applicable in soil

that can be described by an undrained shear

strength of 4 kPa at the surface increasing by 1.5

kPa per meter depth or in the equation Su =

4+1.5*z. with Su in kPa and z being the depth in

meters below seabed. In very soft soils the

optimum fluke/shank angle is typically 50 deg.

The design line sand represents competent soils,

such as medium dense sands and stiff to hard clays

and is based on a silica sand of medium density. In

sand and hard clay the optimal fluke/shank angle

is 32°.

The medium clay design line represents soils

such as silt and firm to stiff clays. The fluke/shank

angle should be set at 32° for optimal performance.

185

Stevpris Mk5

Stevpris Mk5 drag and penetration chart

anchor load drag penetration

as % of % max as % max

UHC drag penetration

70 48 80

60 37 68

50 27 55

40 18 42

30 9 23

Example: loading 70% of ultimate holding

capacity corresponds with 48% of maximum

drag and 80% of maximum penetration at

ultimate holding capacity.

drag

penetration

Stevpris Mk5 size in t

typical drag and penetration in meters

anchor loaded to ultimate holding capacity (UHC)

penetration in sand and hard clay

penetration in medium clay

penetration in very soft clay

drag in sand and hard clay

drag in medium clay

drag in very soft clay

Stevpris Mk6

drag

penetration

Stevpris Mk6 weight in metric tons

in meters in metric tons

anchor load

as % of

UHC

drag

% max

drag

penetration

as % max

penetration

Example: loading 70% of ultimate

holding capacity corresponds with

48% of maximum drag and 80%

of maximum penetration at

ultimate holding capacity.

UHC in medium clay

UHC in very soft clay (mud)

UHC in sand & hard clay

penetration in medium clay

penetration in very soft clay

drag in mrt. in very soft clay

drag in mrt. in medium clay

drag in mrt. in sand & hard clay

penetration in sand and hard clay

drag

penetration

Stevpris Mk6 weight in metric tons

in meters in metric tons

anchor load

as % of

UHC

drag

% max

drag

penetration

as % max

penetration

Example: loading 70% of ultimate

holding capacity corresponds with

48% of maximum drag and 80%

of maximum penetration at

ultimate holding capacity.

UHC in medium clay

UHC in very soft clay (mud)

UHC in sand & hard clay

penetration in medium clay

penetration in very soft clay

drag in mrt. in very soft clay

drag in mrt. in medium clay

drag in mrt. in sand & hard clay

penetration in sand and hard clay

Stevpris Mk6 UHC chart

186

drag

penetration

Stevpris Mk6 weight in metric tons

in meters in metric tons

anchor load

as % of

UHC

drag

% max

drag

penetration

as % max

penetration

Example: loading 70% of ultimate

holding capacity corresponds with

48% of maximum drag and 80%

of maximum penetration at

ultimate holding capacity.

UHC in medium clay

UHC in very soft clay (mud)

UHC in sand & hard clay

penetration in medium clay

penetration in very soft clay

drag in mrt. in very soft clay

drag in mrt. in medium clay

drag in mrt. in sand & hard clay

penetration in sand and hard clay

drag

penetration

Stevpris Mk6 weight in metric tons

in meters in metric tons

anchor load

as % of

UHC

drag

% max

drag

penetration

as % max

penetration

Example: loading 70% of ultimate

holding capacity corresponds with

48% of maximum drag and 80%

of maximum penetration at

ultimate holding capacity.

UHC in medium clay

UHC in very soft clay (mud)

UHC in sand & hard clay

penetration in medium clay

penetration in very soft clay

drag in mrt. in very soft clay

drag in mrt. in medium clay

drag in mrt. in sand & hard clay

penetration in sand and hard clay

Example: loading 70% of ultimate

holding capacity corresponds with 48% of

maximum drag and 80% of maximum

penetration at ultimate holding capacity.

187

Stevmanta VLA

ABC

1600

Stevmanta Fluke Area (m2)

Mooring lines in diameters;

Six strand & spiral strand Spiral strand

ø 76 mm ø 121 mm ø 151 mm

typical installation load in t

typical UPC - Ultimate Pull-out Capacity in t

2000

1200

1000

800



400

200



05 10 25 30

200

400

600

15 20

100

300

500

600



1400

1800

Typical Ultimate Pull-out Capacity (UPC)

The prediction lines on the “UPC chart” can be expressed in the

equations as stated below:

D=1.5 *k0.6 *d-0.7 *A0.3 *tan1.7 (α)

where,

D=Stevmanta penetration depth [m]

k=quotient Undrained Shear Strength clay [kPA] and depth

[m]

d=mooring line or installation line diameter [m]

A=Stevmanta fluke area [m2]

α= Stevmanta fluke / shank angle [deg]

UPC =N

c*Su*A

where,

UPC = Ultimate Pull-out Capacity [kN]

Nc = Bearing Capacity Factor

Su = (k *D), Undrained Shear Strength clay [kPa]

A=Stevmanta fluke area [m2]

The UPC graph incorporates a Nc- value of 10, α-value of 50

degrees and k-value of 2. The graph clearly illustrates the

influence of the diameter of the mooring line or installation line,

and whether six strand or spiral strand is used. The typical

installation load to obtain a specified UPC is presented on the

right vertical axis of the graph.

Stevmanta VLA UPC chart

mooring line types

Comparson chart

188

mbl of various mooring line types

0

5000

10000

15000

20000

25000

30000

0 25 50 75 100 125 150 175 200 225

diameter [mm]

MBL [kN]

weight of various mooring line types

100

200

300

400

500

600

700

800

0255075100125150175200225

diameter [mm]

weight [kg/m]

polyester spiral strand six strand chain hmpe

polyester spiral strand six strand chain K4 hmpe

AMOPMAAK 2005 Voor Pdf Vryhof Anchor Manual

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