Anchor Handling Tug Operations - A practical guide to the operation of modern anchor handling tugs engaged in anchor handling and towing operations

This book sets out in practical and simple terms the theoretical knowledge, methods and techniques that should be used to avoid placing AHTS vessels at unnecessary risk during routine operations. It outlines the forces acting on the vessel and discusses vessel capabilities and equipment. Case studies of the Stevns Power and Bourbon Dolphin are used to illustrate the potential dangers in AHTS operations.

This book will benefit Masters and crew on AHTS vessels, as well as towmasters, rig movers, barge masters, tower foremen and shore-based personnel who utilise these vessels in anchor handling and towing duties.

Scope and purpose of the book

The aim of this book is to give an insight into the operation of Anchor Handling Tug Supply vessels when engaged in anchor handling and towing operations. It is aimed at the masters and officers who operate these vessels and at towmasters, rig movers, barge masters, tower foremen and shore-based personnel who utilise these vessels in their anchor handling and towing roles.

It further endeavours to show, in practical and simple terms, the theoretical knowledge, methods and techniques that can be used to avoid placing these vessels at unnecessary risk when carrying out what, at first sight, appear to be normal operations.

Two recent examples of accidents, resulting in the total loss of AHTS class vessels and their crews, are used to illustrate what can happen and why it can happen – Stevns Power and Bourbon Dolphin.

It must always be appreciated that AHTS vessels are a design compromise and it is this which may lead to over confidence in the ability of a particular vessel to carry out a given towing or anchor handling function.

As the older generation of offshore support vessels is replaced by new tonnage and an older generation of officers and offshore personnel retire, the transfer of experience between generations has not taken place to the extent where all the hard lessons and skills, gained by this older generation, have been fully passed on.

The newer generation of vessels are often of impressive power and specification, but there are dangers inherent in these characteristics which may not always be appreciated by those operating and using them.

The equipment specification of many modern vessels is such that many officers have little time to fully understand the capabilities and limitations of the vessel they are assigned to. Even after serving for some time, there may be gaps in their knowledge which this book hopes to fill and also enable these officers to look more deeply into the equipment they may be using every day.

The reaction by the offshore industry to the loss of AHTS Bourbon Dolphin has been inconsistent, with new rules and procedures recommended by some parties and administrations, but resisted or only partly acted upon by others.

There is also an attitude to these accidents which treats them as ‘unique’ events and therefore they do not hold any particular lessons for the offshore fleet and its personnel.

We do not agree with such an attitude.

Note 1: It is assumed that readers have sufficient knowledge of ship stability to understand the terminology and basic principles of the subject.

Note 2: It is assumed that readers have a working knowledge of the methodologies of anchor handling and towing and are familiar with equipment and vessel type concerned.

Note 3: This book does not deal with the cargo carrying or supply function of vessels classed Anchor Handling Tug Supply vessels. Refer to the Appendix for publications dealing with this aspect of their work.

Part 1 – Theory

Chapter 1 – AHTS power, thrusters, propulsion and steering

Chapter 2 – The environmental forces acting on an AHTS vessel

Chapter 3 – Controlling an AHTS vessel’s thrusters and rudders

Chapter 4 – The effect of a tow on AHTS vessel stability

Chapter 5 – Case studies

Appendix to Part 1 – Possible improvements to AHTS vessel safety

Part 2 – Practice

Chapter 1 – Introduction

Chapter 2 – Basic operational cautions – summary from Part 1

Chapter 3 – Summary of the key points of Part 2

Chapter 4 – The behaviour of AHTS class vessels when going astern

Chapter 5 – Bollard pull certification

Chapter 6 – Turning and manoeuvring modern anchor handling vessels

Chapter 7 – The AHTS design and towing operations

Chapter 8 – The dangers of very high loads during deep water anchor handling operations

Chapter 9 – The dangers of high speed manoeuvring during lay barge operations

Chapter 10 – Some operational characteristics of modern high powered AHTS type vessels

Chapter 11 – Anchor handling loads – basic data required and how to use it

Chapter 12 – Calculating anchor handling loads

Chapter 13 – Guidelines on when to start, cease and re-evaluate the safety of an anchor handling operation

Chapter 14 – Two boat anchor deployment/recovery operations – management of risk

Chapter 15 – ‘Load sharing’ mooring operations – particular risks

Chapter 16 – The responsibilities of personnel in charge of anchor handling and towing operations

Chapter 17 – Instructions to towmasters and rig movers

Chapter 18 – Ship knowledge and practical ship handling exercises

Chapter 19 – Offshore construction operations

APPENDICES

Appendix 1 – Rig move meeting pro forma

Appendix 2 – Reference documents

Appendix 3 – Tugmaster Training – A view by Captain Terry Phillips

Appendix 4 – Further reading

Witherbys

Witherbys titles are developed using scripts developed by technical experts that are peer reviewed within work groups. Typically, they seek to improve understanding of the regulations, recommendations and guidelines issued by Industry.

Witherbys staff have significant expertise in the fields of navigation and hazardous cargoes as well as in the presentation of complex subjects in a graphic and easy to understand manner.