Ship Squat and Interaction

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Number of Pages:
Book Height:
240 mm
Book Width:
190 mm
0.6 kg
Published Date:
September 2009
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This book provides detailed explanations of ship squat and interaction, using worked examples, diagrams, case studies and the author’s personal computations and time-proven formulae.

Ship squat and interaction are major concerns for ship handlers, particularly when operating in shallow waters. This book examines the theory of these forces, how they compromise ship safety and the actions to take to avoid grounding or collision.

The first section of the book lists the signs that indicate when a ship has entered shallow water conditions. It describes methods of measuring squat and looks at the effect of speed on the squat value. Detailed guidance is provided on calculating squat and mean bodily sinkage, as well as the actions a ship can take to reduce squat. The guide provides 15 worked examples that guide the reader through each step of squat calculation.

The second section describes the causes and effect of interaction and identifies the situations in which it is likely to occur. It contains case studies that analyse the causes of various ship incidents related to interaction.

1.1 The Concept

Ship squat is the decrease in underkeel clearance as a ship moves forward after being static. Squat exists when a 3-D body (the ship) proceeds through a 3-D medium (the water). They are connected by a 3-D coefficient (the block coefficient or CB).

Throughout this book, the ratio of the water depth (H) to the ship’s static draught (T) at amidships is for a range of 1.10 to 1.40. Above an H/T of 1.40, there is much less risk of a vessel going aground. Because of the danger of grounding, very few measured squats for full-sized ships are recorded below H/T values of 1.10.

In rivers and canals, a ratio of cross-sectional area of the static ship’s midship section is related to the cross-sectional area of the river or canal. In this book, the ratio is only in the range of 0.100 to 0.250.

Chapter 1 – Introduction

1.1 The Concept

1.2 What Exactly is Ship Squat?

1.3 Who Should Know about Ship Squat and Interaction?

1.4 Ship Squat Measurements – Whereabouts in the World?

1.5 Ship-model Squat Measurements – Whereabouts in the World?

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

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 (y2)

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 Ship’s Path

3.1 Width of Influence

3.2 Depth of Influence

Chapter 4 – Effect of Speed

4.1 Ship’s Speed VK 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

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

12.1 A Brief Introduction

12.2 Case Study 4

12.3 Squat Case Study 5

12.4 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

Number of Pages:
Book Height:
240 mm
Book Width:
190 mm
0.6 kg

Dr Bryan Barrass and Witherbys 

Published Date:
September 2009


  • 5
    Ship Squat and Interaction

    Originally posted on 01/03/2010 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.

  • 5
    Ship Squat and Interaction

    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.