Page 14 - Ship Construction.DJ Eyres 6Ed

Ch01-H8070.fm Page 3 Wednesday, October 18, 2006 6:51 AM

1
Basic Design of the Ship

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The economic factor is of prime importance in designing a merchant
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ship. An owner requires a ship which will give the best possible returns
for the owners initial investment and running costs. This means that the
final design should be arrived at taking into account not only present
economic considerations, but also those likely to develop within the life
of the ship.
With the aid of computers it is possible to make a study of a large number
of varying design parameters and to arrive at a ship design which is not
only technically feasible but, more importantly, is the most economically
efficient.
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Preparation of the Design

The initial design of a ship generally proceeds through three stages: con-
cept; preliminary; and contract design. The process of initial design is often
illustrated by the design spiral (Figure 1.1) which indicates that given the
objectives of the design, the designer works towards the best solution
adjusting and balancing the interrelated parameters as the designer goes.
A concept design should, from the objectives, provide sufficient informa-
tion for a basic techno-economic assessment of the alternatives to be made.
Economic criteria that may be derived for commercial ship designs and
used to measure their profitability are net present value, discounted cash
flow or required freight rate. Preliminary design refines and analyses the
agreed concept design, fills out the arrangements and structure and aims
at optimizing service performance. At this stage the builder should have
sufficient information to tender. Contract design details the final arrange-
ments and systems agreed with the owner and satisfies the building
contract conditions.
Total design is not complete at this stage, it has only just started, post-
contract design entails in particular design for production where the
structure, outfit and systems are planned in detail to achieve a cost and
time effective building cycle. Production of the ship must also be given
consideration in the earlier design stages, particularly where it places
constraints on the design or can affect costs.