Page 168 - Practical Ship Design

134 Chapter 5

graph became outdated well before 1976 because of the growth in ship size and the
change to metric measurements. The 1976 graph has now also been left behind by
a further growth in ship size and indeed this now deters any attempt at a new plot
because the scale required to accommodate the largest ships is so small that the
information it would supply would be almost useless for smaller vessels.
The procedure now suggested involves the addition to the moulded volume of
cargo space of the space required for machinery, oil fuel, fresh water and water
ballast tanks, stores, etc. These can either be estimated as individual volumes and
summed, or alternatively the total volume below the upper deck can be estimated
by the use of a capacity ratio analogous to the deadweight ratio.
The ratio V, IV,, where V, = total volume below the upper deck, can easily be
obtained from any suitable basis ship for which the cargo capacity, dimensions and
speed are known, using the Froude number to estimate the block coefficient C,, and
correcting this to C,,, by the method described in $4.2.3. Although there will
inevitably be some error in this calculation, it is unlikely to be significant.
With vh and cbd known, values of LIB, BID, can be assumed and eq. (3.9) solved
for L.
A quick approximation to the length of a bulk carrier can be obtained from the
formula:

This is derived from eq. (3.9) by assuming values of LIB = 6.25, BID = 1.88 and
cbd = 0.80.
Similar formulae for other ship types can easily be derived from the basic
equation using the constants given in Fig. 3.8 for merchant ships and for warships
in Tables 1.4 and 1.5.

5.2 ESTIMATING THE REQUIRED VOLUME

The other problem posed by “volume type” ships is the determination of the
volume that these must have if they are to fulfil their function. This is a particular
problem in the design of passenger ships and was dealt with at some length in the
author’s 1962 paper. In that paper he felt he had to apologise for giving a list of area
figures for all the different spaces found on a passenger ship, most of which were
common knowledge and all of which could be easily obtained from a study of ships
plans, and said by way of explanation that he had the alternative of either presenting
the bare idea of a volume calculation, which might well have been dismissed as
impracticable, or of supporting this thesis with data that proved its feasibility and
had elected to do this.