Page 149 - Practical Ship Design

I16 Chapter 4

- fuel for main engines
- diesel oil for generators
- sundry engineers tanks
- fresh and feed water
- water in swimming pools
- total deadweight
The deadweight used to determine the load displacement must be the maximum
one that may occur at any point in a service voyage. This will generally occur at the
point of departure from the main fuelling port, but special features of a particular
service in which the quantity of cargo carried differs at different stages of the
voyage may need to be considered. For example, the maximum deadweight of a
fishing vessel will occur at sea when the catch is complete although at this time the
fuel, water and stores can be assumed to be at a reduced level just sufficient to meet
the requirements of the return voyage to port. The same sort of philosophy applies
to tankers bringing cargoes from offshore oil platforms.

4.6.6 Variable loads - warships
Variable loads, which are shown as weight Group 8 in Fig 4.14, are the warship
equivalent of the merchant ship deadweight.

4.7 STANDARD CALCULATION SHEETS FOR INITIAL DESIGN

All design calculations are most conveniently carried out on a standard calculation
sheet although nowadays this may be a prompt on a computer screen instead of a
printed form. One great virtue of a standard format is its ability to ensure that all
significant items are remembered in the hurry in which designs always seem to be
prepared.

4.7. I Standard design sheet for merchant ships

The standard sheet for the design of merchant ships given in the author’s 1976
R.I.N.A. paper is presented as Fig. 4.18. This sheet and its predecessors has been
used for many designs and its use can be recommended with confidence. It has to
admitted, however, that it is now somewhat out-of-date and an alternative is
presented as Fig. 4.19.

Opposite: Fig. 4.18. Merchant ship preliminary design sheet (as presented in Watson & Gilfillan 1976
R.I.N.A. paper).