Stevmanta VLAVertical Load Anchor

Marine operations related tooffshore exploration and

production are moving fast intodeeper water, pushing the

operational limit of existingequipment. On floating units the

weight of the mooring system is alimiting factor and weight savings

are achieved by using differentconfigurations and lighter

materials.

Taut leg mooring

One way to achieve weight savings in a

mooring configuration in (ultra) deepwater

is to use a taut leg mooring. The mooring

lines are much shorter than in a conventional

catenary mooring, thus saving weight.

In the taut leg mooring the unit's movements

are absorbed by the flexibility in the mooring

line, typically provided for by light weight

polyester ropes, so that even further

weight savings can be achieved. As the

anchor line arrives at a 45 degrees angle at

the seabed, a Vertical Load Anchor (VLA) is

required. Vryhof’s VLA, the Stevmanta

has in the last decade been applied around

the world, mooring both semi-permanent

and mobile units.

Vertical load anchor

The Stevmanta VLA was designed to be

installed in the same way as a drag anchor.

A unique and patented system makes the

anchor change from installation mode to

vertical mode which results in an immediate

increase of holding capacity of up to 3.5

times the installation load. It is the lightest

and smallest deep water anchor available

on the market. A full VLA mooring system

can be installed by one anchor handling

vessel in a fraction of the time required for

the installation of other anchored systems.

Thedeepwater solution

Stevmanta VLA

Permanent versus mobile

Mobile Drilling Units (MODUs) have different anchor

requirements than permanently moored systems.

The permanent VLA is designed to meet the strength and

fatigue requirements of a project. The shank is replaced by

4 wires to ensure extreme low installation resistance and

thus deep penetration. The anchor is usually not retrieved.

Anchors for temporary moorings need to be more robust

to withstand repetitious handling, installation and retrieval.

The shank usually consists of chain instead of wire rope.

For retrieval, pulling the anchors with a fraction of the

installation load suffices. Once the chains have been

connected again, the anchor is ready for re-installation.

The MODU advantage

The Stevmanta VLA is suitable for use on a rig and even

allows the rigs to be taut leg moored, so that the much

shorter mooring lines create an obvious weight saving and

a considerable smaller footprint. With a maximum of 100 Ton

winch pull required the VLA can be deployed from a rig's

existing mooring system and chain or wire inserts are no

longer needed. The VLA's installation is conventional

and simple, as is its retrieval. The benefits are clear.

These weight reductions directly benefit the rig's

payload capacity, extending its operational capacity

to much deeper water.

Stevmanta for permanent application Stevmanta for mobile application

Taut Leg Systems

Over a decade of experience with VLA operations generated

vast experience with regard to the ideal installation methods.They are all based on minimizing

time and the number of AHVs required for installing

a full spread.

Single line installation

The Stevmanta is deployed from the AHV

and tensioned to embed in the seabed.

Once it reaches a pre-set load, a shear pin

breaks to release the angle adjuster plate,

adding length to the front wires whereby

the VLA is set in vertical or mooring mode.

Its holding power will have increased by

a factor 3.5 of the pull-in load.

Double line installation

In projects where handling of polyester

ropes dictates the use of a separate

installation line, each line is deployed from

a separate AHV. Both lines are connected to

the angle adjuster and once the installation

load is reached the installation line is

disconnected for instance by means of

a subsea connector. The AHV sails into

the installation direction pulling the

angle adjuster into mooring mode.

Stevmanta VLA

Installationmethods

Drag and position Easy recovery

Installation Methods

45˚

depth

length in soil

ROV

The VLA is unique in that it automatically triggers into

vertical mooring mode to provide the holding capacity.

For permanent systems the installed position and drag are

verified by reading the length marks on the forerunner and

measuring the angle of the anchor line with the seabed.

For each installation method a recovery method for the

Stevmanta is available, typically by detaching the front chains

or wires and pulling the anchor opposite to the installation

direction with a fraction of the installation load.

This method can even be performed with just a single vessel and explains itself visually on www.vryhof.com/2VLAs

www.vryhof.com/singleline w

www.vryhof.com/doubleline

Due to the very high agreementbetween theory and practice

the application of Stevmantasdoes not require extensive

mooring design engineering or extensive soil data.

Its installation does not require expensive rental

equipment such as hammers, ROV’s, pumps and barges.

Stevmanta VLA

MODU applications

The economics of anchoring

In a cost comparison between Stevmanta

and other deepwater anchoring alternatives,

the Stevmanta will prove to be extremely

cost effective as a result of direct and

indirect savings. The cost advantage

provided by the Stevmanta will be larger

with the increase of the waterdepth and

remoteness of the location. The vast field

experience with the use of Stevmantas in

deepwater projects makes it the safe choice.

Lease/purchase

Vryhof's anchors can be supplied on a

purchase or on a lease/purchase basis.

Within a strategic alliance with major

mooring component manufacturers,

Vryhof can design and supply complete

mooring systems. Leasing a complete

(pre-laid) mooring system could well

be a consideration for your next project.

Pre-laid moorings

MODU operators can significantly reduce

mob/demob costs by installing the mooring

spread in advance of the rig's arrival. The rig

can hook-up in only a fraction of the time

otherwise required to pay out a full spread.

By relocating mooring spreads ahead of and

independently from the rig's movements,

the operator can save expensive operational

days within a drilling program to a percentage

of the project costs that might well be

very considerable. The easy retrieval and

turnaround procedure of the Stevmanta VLA

make it the preferred anchor for deepwater

pre-lay mooring systems.

The advantages of using the Stevmanta VLAs in a mooring spread are clear

MODU Applications

• Minimum engineering required• Anchors adjust to soil characteristics• Light weight, easy to install from one AHV• Provides holding power of 3.5 times the pull-in load• Deploys like a conventional anchor• Safe taut leg mooring

Vryhof Anchors has dedicated more than a generation

to the development, manufacturing and supply of high

holding power anchors. Their anchors are recognized

worldwide as weight for weight the most powerful.

Vryhof anchors are now used in every stretch of the

world’s waters and oil field development areas.

Vryhof Anchors BV

P.O. Box 109

2900 AC Capelle aan den Yssel

The Netherlands

Phone: +31 10 266 8900

Fax: +31 10 266 8999

E-mail: vryhof@vryhof.com

www.vryhof.com

Copyright © Vryhof Anchors 2010 | Contents subject to change without notice. Vryhof, Stevin, Stevpris, Stevshark, Stevtensioner, Stevmanta and Stevtrack 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.