Page 333 - Practical Ship Design

290 Chapter 10

be partly filled with liquids must be designed to meet the sloshing loads caused by
the ship's motions in a seaway.

10.2 LONGITUDINAL STRENGTH

Although as already stated, most Classification Society rules tend to be complex,
some remain quite simple and it is possible to give one brief extract from rules now
agreed by all the Classification Societies as I.A.C.S. requirement S11 which can be
used in advance of detailed longitudinal strength calculations to give a first approxi-
mation to the required midship section modulus.
The minimum midship section modulus Z about the transverse neutral axis at
the deck or at the keel is not to be less than:

Z= f, . k, . C, . L2(Cb + 0.7) x 10" m3
The wave bending moment is to be taken as:

M, =f1 .fi. M,,
In these formulae
fi = Ship service factor = 1 for unrestricted service
0.8 for short voyages, and
0.5 for sheltered water
f, = -1.1 for the sagging moment
1.%,
- for the hogging moment
-
(C, +0.7)
k, = steel strength factor
= 1 for mild steel
= 0.78 for 315 N/mm2 higher tensile steel, and
= 0.68 for 315 N/mm2
C, varies with ship length, but typically for the main range of ship sizes (90-300
m) is:
(300 -L)
Cl = 10.75 -
100
C2 is a factor depending on the position along the ship's length = 1 .O for amidships

M,, = 0.1 C, ' C2 ' L2 ' B ' (cb + 0.7) kN m
Taking the sagging moment case, the allowable stress built into these formulae
is: