Page 323 - Introduction to Naval Architecture

308 SHIP DESIGN

between cost, weight, volume, reliability and maintenance load. Here
not just the machinery but such things as fuel, gearing, seatings,
uptakes and down takes must be taken into account. The final decision,
however, may be strongly influenced by the type of machinery fitted in
others of the owner's ships. If the others all have diesels, say, it would be
expensive to change to gas turbine because of the added training and
logistic costs.

General
It would be possible to discuss many other features of the design here
but the above should give the reader a feeling for the considerations
involved. Some special features associated with different ship types are
discussed later.

EFFICIENCY

To be efficient a ship must be able to carry out its intended functions
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economically ' and be available when needed.

Economy
Costs are always important. Unless those of a merchant ship are less
than the revenue they can earn the ship will be a liability. For
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warships, which cannot 'earn' in the commercial sense ' the cost
effectiveness of a design is harder to define let alone assess. In the
end the warship designer can only inform the naval staff of the
cheapest way to meet the requirement It has then to be decided
whether this amount of money can be allocated from the defence
budget against the competing bids of other requirements. If not, then
the requirement must be reduced till an acceptable balance is
achieved between need and affordability. The costs should be the
through life costs, not just the build costs. Thus it might be better to
use more mechanization to reduce crew size if the cost of mechaniz-
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ing is less than the associated crew costs over the life of the ship.
These are not easy balances to assess. The crew not only need to be
paid, they must be trained, they need space on board and so on.
Mechanization will bring with it initial and maintenance costs, with
the need for maintainers offsetting other crew reductions.
Assuming the ship can earn revenue this can be assessed for the years
ahead using the anticipated freight rates. Build costs will arise early on
and then operating costs, including costs of crew, bunkering, port
charges, refitting and repair, will be spread over the life cycle. At the
end of the day the owner hopes there will be a profit. Depreciation
must be allowed for although it is not an item of cash flow.