Page 178 - Practical Ship Design

144 Chapter 5

5.4 OTHER “VOLUME DESIGN” SHIP TYPES

There are quite a number of other ship types which are best designed by calculating
the total enclosed volume required to accommodate all the spaces needed for the
crew and the various activities which they undertake. These include: fish factory
ships, offshore safety ships, livestock carriers, oceanographic and fishery research
vessels amongst merchant ships. However, possibly warships of frigate and
corvette types are the largest and most important category of volume-based ships,
although because these ships are also usually designed for minimum weight some
designers tend, erroneously, to regard them as weight-based designs or claim that
they are balanced designs in which weight and volume are equally important.
The warship design calculation sheet given as Fig. 4.19 includes a section for
the calculation of the total internal volume. It would have been nice to supplement
this with a series of guidance notes on the completion of this form to parallel those
given for passenger ships, but as all the data that the author has on this subject was
derived from plans subject to security classification, readers must be left to
formulate their own approximate algorithms.
It can, however, be confidently asserted that this design method can be applied
to warship design with considerable advantage.

5.5 CREW NUMBERS
5.5.1 Passenger ship crew numbers

In $5.2 the need to know what constitutes a suitable crew was noted in relation to
passenger ship design but of course the same applies to the design of all ship types.
In the 1976 paper it was noted that the passengerkrew ratio for passenger ships
had not changed much from that noted in 1962. This seemed surprising when
related to the very significant reduction in the crews of cargo ships over the same
period, but the explanation lay in the higher standard of hotel services being
provided, which offset reductions in deck and engine department manning fairly
similar to those on cargo ships.
Ships in 1976 were seen to group into passengerkrew ratios of about 1.7 to 2.2
for ships aiming at the upper end of the cruise trade with ratios of 2.5 to 3.0
applying to ships catering for the more popular end of the trade. In both cases the
lower figures applied to the smaller ships and the higher ones to the larger ships.
In 1992 the passenger/crew ratio for “Fantasy” was 2.86.

5.5.2 Cargo ship crew numbers
In 1976 the change in manning since 1962 was seen to have come about as the
result of a felicitous conjunction of motive and means: the growing pressure for