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Chapter 4

Weight-Based Designs

4.1 INTRODUCTION

The first part of this chapter deals with the estimation and calculation of the
lightweight and deadweight which make up the displacement.
The components of the lightweight in merchant ship practice consist of the
structural weight, the outfit weight, the machinery weight and the margin. Warship
designers use a larger number of weight groups, as shown in Fig. 4.14, but for
convenience, warships are also considered here under the three merchant ship
groups.
A number of approximate estimating methods are given for each of the weight
groups and these are followed in each case by a suggested format for the detailed
calculations which should follow as the design is developed.
The later sections of the chapter deal with approximate methods of estimating
the lightship VCG and LCG and the maintenance of control over the weight as the
design develops.
The term “weight” has been used as this is common parlance although scienti-
fically the term “mass” would, of course, be correct.

4.1. I Demarcation of the weight groups
The demarcation between the three weight groups of structure, outfit and machinery
is not as obvious as it might appear at first sight as there are several items which
could logically be placed in more than one group. It is therefore very desirable to
have a demarcation that is standard at least within a design office.
In general, the structural group includes all steel or other structural material
worked by the shipyard plus such items as deposited weld metal or rivet heads.