Overview
This book has been revised and updated following publication of the MCA’s 2018 Second Edition of the Workboat Code.
It provides an introduction to ship stability, weight, centre of gravity and hydrostatic information, and then guides the reader through the calculations necessary to maintain buoyancy and stability. It discusses how to conduct inclining experiments and roll tests and how to use the results.
Detailed information is provided on loading condition and free surface effects, together with calculation of the associated flotation and stability characteristics.
Further chapters cover stability acceptance criteria, trim, the downflooding angle, damage survivability, the use of lifting devices and the stability of sailing vessels.
The metric system of measurement is used throughout and the author’s original hand-drawn sketches have been retained to illustrate the text.
The author hopes that the reader, who develops an understanding of the subject matter, will then be able to follow the Safety Codes and the ISO Standards, and will begin to understand some of the important basics of naval architecture that keep ships and small vessels The Right Way Up.
Content
Contents
Other Books in this Series iii
Foreword v
Second Edition vi
Introduction vii
Recreational Craft Directive – Cautionary Note – ISO 12217 Stability Assessment ix
Chapter 1 Introduction to Stability 1
1.1 Background 3
1.2 Definitions 3
1.3 Symbols 4
1.4 Initial conditions of stability 6
Chapter 2 Weight and Centre of Gravity 9
2.1 Initial estimate of Lightship Weight and Centre of Gravity 11
2.2 Estimate of vessel weight (Displacement) and CG in operation 11
Chapter 3 Hydrostatic Information 13
3.1 Hydrostatics 15
3.2 Righting Levers 15
Chapter 4 Keeping the Vessel Upright 17
4.1 Metacentre (from the Greek μετα: ‘After’ – i.e. calculated fro, known factors) 19
4.2 Stability at small angles and GM 23
4.3 Stability at larger angles and the GZ curve 24
Chapter 5 The Inclining Experiment 27
5.1 Why is it done? 29
5.2 How is it done? 29
5.3 How do you use the results? 32
Chapter 6 Alternative Stability Checking by Roll Moment 39
6.1 Background 41
6.2 Principle and procedure 41
6.3 Roll moment method – summary 42
Chapter 7 Loading Conditions 45
7.1 Loading Condition 47
7.2 Free Surface Effects 48
7.3 Typical GZ curve 52
7.4 Maximum permissible KG curve 53
Chapter 8 Stability Acceptance Criteria 55
8.1 Normal acceptance criteria for a vessel 57
8.2 Acceptance criteria for a catamaran or multihull vessel that cannot meet the requirements of 8.1 58
8.3 Acceptance criteria for motor vessels complying with Annex Section 11.1.1.3 58
Chapter 9 Trim 61
Chapter 10 Downflooding Angle 67
10.1 What is the Downflooding Angle? 69
10.2 Critical Angle of Downflooding 69
Chapter 11 Damage Survivability 71
11.1 Floodable length curves 73
11.2 Damage stability 76
11.3 Criteria for damage stability assessment 77
Chapter 12 Cranes and Suspended Weights 79
12.1 Fitting a crane 81
12.2 Stability considerations 81
12.3 GZ and heeling curves 81
12.4 Criteria for acceptance of vessel with lifting device or crane 83
12.5 Crane testing 83
Chapter 13 Stability of Sailing Vessels 85
13.1 Background 87
13.2 Wind curves 88
13.3 Gusts and Squalls – definitions 89
13.3.1 Preventing downflooding in Gusts 89
13.3.2 Preventing downflooding in Gusts and Squalls 91
13.4 Sailing multihulls 93
13.5 STOPS Numeral 94
13.6 Stability and safety screening: the SSS Numeral 96
13.7 The stability index: STIX 96
References 99
Appendices 103
Appendix 1 105
Appendix 2 108
Appendix 3 109
Appendix 4 110