Page 371 - Practical Ship Design

328 Chapter I I

Finally, however, it may be necessary to make the compartments smaller than has
been past practice by introducing one - or on larger ships possibly two -
additional bulkheads to improve pi. On gearless bulk carriers or container ships the
extra cost of this will not be very great. On ships with cargo handling gear and on
refrigerated ships the extra cost of another hold will be considerable and it may pay
to look instead at increasing the freeboard to improve si - either increasing the
depth (but stability must be watched), or reducing the draft or both.
It is clear that these rules require a major rethink about many things that have
been accepted practice in ship design.

11.7 PROBABILISTIC RULES FOR PASSENGER SHIPS

This brief treatment is intended to highlight the main differences from the cargo
ship rules dealt with in the last section.
The required subdivision index R for passenger ships brings in a factor increasing
the standard with the number of passengers and crew carried as compared with
cargo ships in which ship length is the sole factor.
1000
R=l-
4L, +N, +2N, +1500

where
N, is the number of persons for whom boatage is provided, and
N2 the remainder of the complement.
The formula for the Attained Subdivision Index is:

A = Ca .p. s

This looks different from the cargo ship formula:

but in fact for much of a cargo ship pi = p . a.
On passenger ships, unlike cargo ships, the vertical extent of damage is from the
base upwards without limit - although this is qualified in the damaged stability
rules by the statement that if a lesser extent of damage is more onerous this must be
considered.
In the probability calculations for passenger ships four drafts must be considered
as opposed to two for cargo ships.
The formula for p for each compartment appears to have a different basis from
that in the cargo ship rules, although this may be more in presentation than in