Ship Squat and Interaction

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Published Date

September 2009

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Ship Squat and Interaction

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Ship squat and interaction are major concerns for the handling of ships, particularly in

shallow waters. This book provides detailed explanations of these conditions,

using worked examples, case studies and the author’s personal computations and time-proven


The phenomena of both Ship Squat and interaction are a major concern for the handling of ships, particularly when ships are operating in shallow waters. Ship Squat can be defined as ‘the decrease in underkeel clearance as a ship moves forward after being static’, this book aims to give a more thorough understanding of these conditions, based on the authors work in this particular area since completing his PhD on the subject in the early 1970s.

After decades advising operators, pilots and port authorities on this subject matter, professionals in these positions or Shipowners & Operators, Mates, Masters, Tug Operators, Educational Establishments, Ship-model Tank staff, Ship Simulator staff and Maritime Examiners will find this book to be of great use.

A great commentator on these subjects over the years in the maritime press, this book brings together the work of Dr Barrass in a single publication and is a comprehensive work on this interesting subject that is often not well understood in the marine industry.

Chapter 1 Introduction


    1. The Concept

    2. What Exactly is Ship Squat?

    3. Who should know about Ship Squat and Interaction?

    4. Ship Squats Measurements – Whereabouts in the world?

    5. Ship – model Squat Measurements – Whereabouts in the world?

    6. Why has Ship Squat Become so Important in the Last Forty Years?

End Note



Chapter 2 Recent Incidents and Tell Tale Signs


2.1 Recent Ship Groundings and Sinkings

2.2 Static Underkeel Clearances

2.3 Dynamical Underkeel Clearances (y/2)

2.4 United Kingdom Merchant Shipping Notices

2.5 Fifteen Signs that a Ship has Entered Shallow Water Conditions


Chapter 3 Depth and Width of Influence of a Ships Path


3.1 Width of Influence

3.2 Depth of Influence


Chapter 4 Effect of Speed


4.1 Ship’s Speed V/K in a River having a Tidal Flow or Current


Chapter 5 Measurement of Ship’s Squat


5.1 The Measurement of Ship Squat on Full – size Ships

5.2 Case Study 1 – Measurement of Squat at the Entrance to a dock

5.3 Conclusions

End Note


Chapter 6 Increase and Decrease of the Squat Value


6.1 What are the Factors Governing Ship Squat?

6.2 Silt Saucers and Dredging

6.3 Angles of Heel

6.4 Squat Formulae

6.5 Three Worked Examples


Chapter 7 Squat Curves


7.1 Squat Curves

7.2 Squats Predicted for a Very Narrow River up to a Very Wide River

7.3 Asymptotic Squats


Chapter 8 Squat when Trimmed and Steps to Reduce Squat


8.1 Ship Squat for Ships with Static Trim

8.2 Squats at Both Ends of a Vessel in Open Water

8.3 Worked Example

8.4 Procedures for Reducing Ship Squat

8.5 False Draughts

8.6 Ship Squat Laminates


Chapter 9 Mean Bodily Sinkage


9.1 Mean Bodily Sinkage in Open Water Conditions


Chapter 10 Using Squat to Assist In the Reduction of Air Draught


10.1 Introduction

10.2 General Particulars of ‘Freedom of the Seas’

10.3 Definition

10.4 Nomenclature

10.5 Prerequisite Information

10.6 Procedure

10.7 Formulae

10.8 Points to Consider Regarding Static Trim

10.9 Worked Example

10.10 Summary and Conclusions


Chapter 11 Using Spreadsheets to Determine Squat


11.1 The All – Encompassing Method

11.2 Case Study 2 – Cross Channel Ferry Squats in the Port of Newhaven

11.3 Case Study 3 – Squats in a Navigable Trench (Melbourne)


Chapter 12 Incidents in Shallow Water


    1. A Brief Introduction

    2. Case Study 4

    3. Squat Case Study 5

    4. Squat Case Study 6


Chapter 13 Calculated v Measured, How Accurate?


Chapter 14 Final Summary and Conclusions


14.1 Nomenclature

14.2 Ship Squat Formulae

14.3 Merchant Ship Types – General Characteristics

14.4 Ships of this Millennium

14.5 Questions and Exercises on Ship Squat
14.6 Fifteen Worked Examples

Dr Bryan Barrass has worked in the shipping industry since 1953, resulting in over 50 years of industrial, lecturing and research experience to date.

He commenced as a Ship Draughtsman, working for 11 years at the Swan Hunter shipyard in Wallsend. In 1963, he became a Lecturer in Naval Architecture in Sunderland. From 1967 to 1993, he worked at Liverpool John Moores University, lecturing to Maritime Degree students, Masters, Mates and Marine Engineers.

In 1993, he retired from full-time work. He became a visiting Lecturer and authored six books on ship stability, ship squat, ship design and ship performance. His interest in ship squat began in April 1972, starting on research for his PhD degree. He has lectured part-time at six UK universities, as well as in Singapore and Australia.

Dr Barrass has supplied information on squat worldwide to shipowners, academia, maritime institutions and consultants, and maritime journals. He has also worked with many Port Authorities, including the Port of London Authority, Milford Haven PA, Liverpool PA, Humberside PA, Tyne PA, Truno PA, Newhaven PA, Bordeaux PA, Klaipeda PA, Nantes PA and Hamburg PA.

Title: Ship Squat and Interaction
Number of Volumes: 1
Edition: First
Number of Pages: 182
Product Code: WS1062K
ISBN: ISBN 13: 978-1-905331-60-4 (9781905331604), ISBN 10: 1-905331-60-6 (1905331606)
Published Date: September 2009
Binding Format: Paperback
Book Height: 240 mm
Book Width: 190 mm
Book Spine: 10 mm
Weight: 0.60 kg
Author: Bryan Barrass

Customer Reviews

Ship Squat and Interaction Review by Captain Hugh N. McQuaid. MRIN. MIQA. Director. Marcon Associates Limited
The advent of smaller bridge management teams, yet again highlights the need for the advanced passage planning requirements to give detailed analysis of the arrival tidal conditions, linked in with prevailing weather conditions that may or may not influence berthing ranges at the next port. These calculations must be seriously reviewed by both the Ship Master, Ship Owner, Port Managers and Pilots to ensure safe passages of vessels using their ports. This also has an impact on other vessels movements, that by draught constraint, are required to sail or arrive at the same time, again increasing the need for risk analysis on the effects that squat and inter-ship interaction can cause, especially in canals and narrow channels. I would also recommend the book to Large Yacht Masters as well as Brokers and Management Company’s. These vessels are increasing in size year on year, yet Owners still wish to visit the most popular destinations. The increase in size is a correlation between draught and speed, while in the majority of cases the Yacht Masters do their own pilotage. Therefore, the need for more diligence is required for a more professional understanding of the subject. I particularly like the individual highlighted icons on selected pages that readily bring the readers eye to the important sections on that page.The mass of mathematical formulae for the academics is giving all readers a more detailed understanding of the theories behind the numerous calculations to be found in this book.

Dr Barrass, has again provided the professional mariner and port operator, with a valuable tool to enhance their understanding and appreciation of this extremely important aspect of the mariners professional and operational expertise.
(Posted on 01/03/2010)
Ship Squat and Interaction Review by Nautilus Telegraph Review
Regular Telegraph readers probably need little introduction to the problems posed by ship squat: it’s a subject that has featured all-too regularly in accident reports, and has prompted contributions to the paper by Dr Bryan Barrss, one of the world’s leading experts on the subject. Now Dr Barrass – a former naval architect and university lecturer – has produced a 180-page book that addresses both ship squat and interaction, seeking to give everyone in the shipping industry a better understanding of the dangers that they can present. With the aid of excellent graphics, the book demonstrates why squat has become an increasingly important issue within shipping safety. The big increase in average ship sizes and speeds, coupled with poor dredging in many areas, has led to dramatic decreases in static underkeel clearances – with Dr Barrass referring to more than 110 groundings that resulted from excessive squat. Using case studies and worked examples throughout, the book examines the factors that influence squat and interaction – including speed, and water depth and width, as well as ship-to-ship and bank effect. It also sets out squat curves and formulae to assist owners, operates, officers and pilots in safe passage planning and gives advice on using spreadsheets to determine squat together with guidance on reducing the impact of interaction in such scenarios as river and canal passages replenishment at sea and drydocking. Dr Barrass completed his PhD on the subject in the early 1970s, and this clear and comprehensive book will surely serve as the definitive publication for the industry piece by Bob Wilson, who wrote the Telegraph’s popular Ships of the Past feature for the best part of a decade – and many other well-known figures have contributed, including the marine artist Geoff Hunt. The book opens with an interview with the director of the National Maritime Museum, in which he discusses the plans for the museum’s model collection. At £30, the book isn’t cheap, but it is very well presented, with high quality paper, hardback binding and glossy photographs, and it is a publication that enthusiasts will want to keep for future reference. (Posted on 01/10/2009)

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