Page 139 - Practical Ship Design

106 Chapter 4

Noted since 1976:
- reductions in crew numbers and corresponding reductions in accommodation
area - most ships
4.4.4 Detailed outfit weight calculations - warships.

It has already been noted that outfit is a merchant ship concept and that its use
for warships must be subject to some definitions.
On warships both weight and cost recording and estimating systems make no
demarcation between the hull and the machinery spaces, with everything being
divided into eight groups irrespective of location. This is undoubtedly a very
sensible procedure for warships where machinery, accommodation and weapon
systems are very much intermingled.
These groups are shown in Fig. 4.14, which has been abstracted from David
Andrew’s 1993 R.I.N.A. paper “Preliminary warship design” and are used in the
warship preliminary design sheet (Fig. 4.20).
For the reasons advanced in $4.4.1, the warship weight groups have been
divided in this book into an approximation to the three merchant ship categories.
This involves taking Group 1 as structural, Groups 2 and 3 as machinery and
Groups 4, 5, 6 and 7 as outfit, with Group 8 being the warship equivalent of the
merchant ship deadweight.
It must be admitted that the equivalence is by no means accurate as Group 3
certainly includes items outside the machinery spaces whilst Groups 4 and 5
include machinery items as will be clear from the subdivision of these groups
given in Fig. 4.14. This subdivision stops at a limited number of main headings but
warship designers use a much more detailed standardised format.
The reasons for the changes in outfit weights of approximately similar ships
which have occurred in recent years are worth noting.
Factors leading to increases in weight:
- the increased weapon carrying ability now demanded; more bangs for fewer
bucks!
- emphasis on zoning and survivability;
Factors leading to reductions of weight:
- significant reductions in crew numbers;
- reductions in accommodation joinenvork (this change has been made primar-
ily to reduce the fire hazard in these ships);
- reductions in the weight of weapon control systems and data highways using
modern computer techniques;
- the much greater attention now paid to detail in the design of many relatively
unimportant items of outfit, which were unreasonably heavy in the past for
ships where weight was of such importance.