Page 66 - Practical Ship Design

Setting Design Requirements 37

Table 2.1
Three important dimensional restraints
Max. length Max. beam Max. draft Air draft
(m) (m) (m) (m)
Panama Canal* 289.56 32.3 1 12.04 TFW 57.91 m
SueL No restriction 74.0 and 1 1 .o
or 48.0 and 17.7
St. Laurence 225.5 23.8 8.0 35.5

*294.13 m for passenger and container ships. Reduced dimensions apply to some special types of vessel.
Addresses of these authorities are given in Chapter 19.

permissible mean draft, in association with a trim that maximises the draft at the
fore and aft position of the highest point of the ship. Three of the most important
dimensional restraints are given in Table 2.1.

2.3 ENVIRONMENTAL CONDITIONS

The wind and sea states in which a ship is required to operate are major factors to
be considered in its design, although for the majority of merchant ships these states
are not mentioned in the specification, their place in that document being taken by
a Classification Societies notation "100A 1 " or similar, denoting an ability to trade
worldwide in ice-free waters. For ships intended to trade only in sheltered waters
reduced strength and other requirements are permitted by classification societies,
IMO rules and those of national authorities. If it is intended to take advantage of
these concessions and the reduced associated costs, the trading limits within which
the ship will operate must be clearly defined.
For the other categories of ships shown in Fig. 1.2, namely warships and naval
auxiliaries, service ships and floating production vessels, it is essential to define
the wind and sea states in which the ships are required to carry out various tasks.
Three sets of conditions are usually defined for warships. The first defines wind
and sea states in which the ship should be able to maintain its full service speed and
operate all its equipment at maximum efficiency. The second is a more severe set
of conditions in which a reduced speed is acceptable, but the ship must still be able
to operate its helicopter and other weapon systems, possibly with some reduction
in performance. The third is a still more severe set of conditions in which
survivability is the requirement.
For an oil production vessel there will be generally be two sets of conditions:
one in which production must be able to continue and another in which production
will be shut down and the safety of the vessel and crew becomes the design