zxc ® 16-Mar-2015 20:04

The Management of Merchant Ship Stability, Trim & Strength

Year: 2002
Language: english
Author: I.C. Clark BSc MSc
Publisher: The Nautical Institute of London
ISBN: 187 00 77 59 8
Format: PDF
Quality: Scanned pages + text layer
Pages count: 303
Description: Soon
Additional info: A guide to the theory, rules and calculations carried out to ensure that a vessel maintains seaworthy stability and trim whilst remaining within its limits of strength.
Ian Clark started his sea-going career in 1969 as a cadet with the Ocean Steamship group, serving on general cargo ships trading from Europe to the Far East and West Africa. He then worked as third and second mate with P&O General Cargo group, the British Antarctic Survey and Bank Line, during which time he gained his First Certificate and BSc in Nautical Studies from Liverpool Polytechnic.
Mr Clark then left the sea in 1978 to become a secondary school physics teacher for twelve years, during which time he also studied for an MSc in Marine Geotechnics at Bangor University and designed and built a 28 foot racing yacht in partnership with a friend. He returned to the Merchant Navy in 1990 as first mate on small survey ships working in the North Sea, gaining his Master's certificate in 1992, and has since worked mainly on off-shore support vessels with some relief work on ro-ro ferries. He is currently Chief Mate on cable ships with Global Marine Systems.
In writing this book, he has explained the principles of applied physics that underlie the subject whilst always trying to keep the various aspects of trim, stability and strength within a practical context. An aspiring marine officer should find the different sections of the book useful throughout their career at sea, from cadet to marine superintendent.


1) An Introduction to the shape of a ship’s huilform and the principles of hydrostatics that act upon it.
Basic requirements of a good huilform. Definitions of hull measurements and features. The linesplan and table of offsets. Calculations for waterplane areas and submerged volume. The basic principles of buoyancy and floatation. Definitions ofT.P.C. and F.W.A. An introduction to the principle of moments with regard to the forces of Weight, acting through the ship's Centre of Gravity, and Buoyancy acting through the immersed hull s Centre of Buoyancy. Definitions of a ship s motion in a seaway and the basic features of seawaves.
2) Locating the Centre of Buoyancy for different angles of heel.
Introduction to changes of a hull’s underwater shape with changing angle of heel. The shift in the Centre of Buoyancy off the centreline towards the low side of the ship and how this can produce a Righting Moment, providing that the C of B is outboard of the Centre of Gravity. The Righting Lever GZ defined.The Metacentre 'M' defined as the point at which the C of B rotates about during a small change in heel angle. The upright GM value is introduced as a measure of stability. The effects of hull beam and draft on the upright BM value and the changes in both the Metacentre s position and BM value with increasing angles of heel. The Wall-sided equation is explained and the Trapezium rules are used to show how the Centre of Buoyancy can be located at different angles of heel by applying the principles of moments to areas and volumes derived from the tables of offsets. KN Curves are defined as the means of expressing this shift of'B ’.
3) Transverse stability characteristics and the GZ Curve.
Stable, neutral and unstable conditions are defined in terms of the Centre of Buoyancy 'B the Centre of Gravity G' and the Metacentre ‘M'. The GZ curve is used to illustrate how a vessel s transverse stability changes with increasing angles of heel The effects of a hull s beam, freeboard, draft, fineness of lines and sheer upon the GZ curve are discussed. The six basic criteria of seaworthiness, which must be met by a ship's GZ curve, are defined with an alternative set of criteria for High Fo 'c ’sle vessels.
4) Operational transverse stability.
The inclining experiment is explained as the means by which the Lightship KG value is measured. The loaded KG calculation is described by applying the Principle of Moments to the known loaded weight distribution. The Free Surface Effect ofpartly filled tanks and its importance in stability calculations is explained. The process of drawing an actual GZ curve from the supplied KN curves and the calculated fluid KG value is described. Use of simplified stability data diagrams. Calculating the heeling moment and list when ‘G' is not on the centreline. Calculating the increase in draft due to a list. The effective centre of gravity of suspended loads and the stability calculations involved in loading a heavy lift. Heeling effect due to a ship turning under the action of the rudder. The unstable upright condition and the Loll angle are defined and procedures for regaining stability are outlined. A study into an incident of loss of stability in the case of a ship loaded with timber.
5) Stability requirements for ships operating wider special circumstances.
Passenger vessels. Ship s carrying deck timber cargo. Ships carrying solid bulk cargo, including grain. Ships operating heavy lifts at sea. Windage allowance for ships carrying high deck stows of containers and ships operating in high latitudes where ice build up is a danger.
6) Longitudinal stability and practical trim calculations.
Longitudinal Centre of Buoyancy (LCB) and Longitudinal Metacentre. Longitudinal righting moments. The trim axis and centre of floatation (LCF), location of LCF for a given draft, shift in the LCB due to change of draft, estimating the longitudinal BM value for a vessel, the moment required to change trim by lcm (MCTC). Taking moments of weights about the aft perpendicular (AP) to predict a ship 'sfore and aft drafts. Average and mean drafts defined. The change of trim due a fore and aft shift of weight. The change of trim when moving from salt to fresh water. Trim and stability calculations during drydocking. Beaching and stranding.
7) A ship’s motion in a seaway and anti-roll measures.
The Simple Harmonic nature of a ship s natural roll period. Determining a ship s radius of gyration. Estimating the natural roll period in terms of ship s beam and GM values. Synchronised rolling. The effect of bilge keels. The action offlume tanks. Managing a ship in heavy weather to minimise rolling. Torsional and wracking stresses induced by rolling.
Active anti-rolling devices, gyroscopic controlled stabilisers. The pitching characteristics of a ship. The natural pitching period of a ship. The pitching characteristics of a ship in a seaway. The problems of exceptional head seas. Pitch induced or parametric rolling.
8) Shear forces, bending moments and longitudinal strength.
The elastic properties of shipbuilding materials. Shear forces and bending moments defined. Longitudinal bending in a ship’s hull, hogging and sagging. Bending moment calculations for a box shaped hull in various loaded conditions. The weight distribution of a ship. The still water buoyancy distribution of a ship shaped hull. Changes of buoyancy distribution in a seaway. Bonjean curves and Muckle’s method for buoyancy distribution calculations. Bending stresses defined. Moments of Inertia for different girder sections. Stress calculations for a ship s midships section. Stress distribution within a ship’s structure. Composite hulls. Cracking. Some brief notes on shipbuilding methods.
9) The consequences of flooding through bilging.
The term ‘bilging’ and its effect upon a ship’s draft, trim and stability explained. The ‘lost buoyancy’ approach to bilging calculations is compared to the ‘added weight’method. Stability and trim calculations by the 'lost buoyancy ’ method explained by examples of bilging different compartments in a box-shaped hull. Permeability of partially loaded spaces defined. Predicting the effects of bilging different compartments in a real ship. The consequences of bilging a real ship and the need for cross flooding examined. Comparison made between the sinkings of the ‘Titanic ’ and ‘Andrea Doria ’.
10) The ‘SOLAS’ subdivision and damage stability requirements for passenger ships and cargo vessels and the ‘MARPOL’ tanker subdivision regulations.
These rules are explained and examined with regard to their effects upon a ship s damage stability and trim.
11) The International Load Line regulations for merchant ships.
An outline to the background and aims of the load line regulations. Terms used in the regulations defined. Loadline markings described. Conditions of freeboard assignment explained. Tabulated and corrected freeboard explained. Seasonal and regional load lines explained. Compliance with the regulations explained.


Rating: 4.9 / 5 (Votes: 53)
khany 13-Aug-2018 12:08
The year of publication of this book is wrong, it is 2002 not 2011. There is a second edition of 2008 with different title.

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