Page 320 - Introduction to Naval Architecture

SHIP DESIGN 305

system as ships already in service, and so on. The owner may employ a
naval architect to facilitate this discussion but the aim should be to state
the 'operational' needs and leave the designer to decide upon the best
means of achieving them. Thus in seakeeping any desired limits on
rolling motion should be stated, leaving the designer to decide whether
roll stabilizers are necessary and, if so, which would be the best type. On
the other hand, the owner may specify that the main machinery is to be
of a certain type because there are already a number of ships with this
machinery in the company's fleet. To adopt different machinery would
complicate the training of personnel and make logistic support more
costly. Ideally there will be close collaboration between the designer
and owner to ensure that the requirements specified are sensible,
taking account of past practice but also taking advantage of developing
technology. Thus new outer bottom coatings may make it possible to
adopt longer intervals between dockings.
In the case of British warships it is the naval staff of the Ministry of
Defence (MOD) who set out the requirements for new ships. Initial
discussion with the MOD's own designers will lead to a series of design
studies. These are taken by high level committees and gradually the
basis for the new design emerges. 1

Some design features
Capacity and size
Usually there will be a certain volume of goods the ships of a fleet
need to carry. This may have been established by a market survey.
The 'goods' may be cargo, people or weaponry. The amount to be
carried in an individual ship will depend upon the rate at which
goods become available. This will depend in turn upon the support-
ing transport systems on land. Taking ferries as an example, one
super ferry sailing each day from Dover to Calais, capable of carrying
one day's load of lorries, cars and passengers, would not be popular.
Transit for most would be delayed, large holding areas would be
needed at the ports and the ship would be idle for much of the time.
Whilst such an extreme case is clearly undesirable it is not easy to
establish an optimum balance between size of ship and frequency of
service. Computer modelling, allowing for the variability of the data,
is used to compare different options and establish parameters such as
the expected average waiting time, percentage of ship capacity used,
and so on.
There may be limits imposed on size by external factors such as the
geographical features, and facilities of the ports to be used and the
need to use canals. The Suez Canal may limit the draught and the
Panama Canal the maximum beam.