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INTRODUCTION

The ability to conduct military operations at sea has long been of paramount strategic importance for all maritime nations. Defence of trade and prevention of seaborne attack are vital roles. In addition the ability to conduct offensive operations widens political options and can act as deterrence in its own right. The fulfilment of these objectives in a wide range of operating conditions and threat scenarios results in the need for military craft with a wide range of characteristics. Some may need to fulfill several roles, others may need to be optimised for particular roles. In either case the demand to obtain value for money places ever- increasing pressure on the correct selection and design of naval combatants.

The marine environment will always place limits on the speed, manoeuvrability and seakindliness that can be achieved by any craft designed to operate within it. The design of military marine craft hull types has for long been dominated by the single hulled-displacement craft, or monohull, and this has reached a high state of development. It can be readily tailored to particular applications, for example the planing form where the aircraft weight is supported by dynamic lift in order to reduce high speed resistance. However, all designs involve a compromise, and there are inherent limits on the performance that can be achieved by a particular design concept.

It is in order to extend these limits in particular areas of performance that craft with unconventional hull types have evolved. The term unconventional hull type is here taken to mean any craft that is not of conventional monohull displacement or planing form. This includes craft such as hydrofoils where the hull is supported by under water foils, multihulls such as catamarans with two hulls or trimarans with three, Small Waterplane Area Twin Hull (SWATH) vessels, and craft wholly or partly supported by air pressure, such as Air Cushion Vehicles (ACVs) and Surface Effect Ships (SESs).

The need to obtain ever more value for money in all areas of defence procurement has led to the development of Cost and Operational Effectiveness Analysis as an essential element of the decision making process for all acquisition programs. The purpose of this document is to present sufficient data to allow the application of such cost and operational effectiveness methods to the initial selection of hull types for naval applications.

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