Page 136 - Practical Ship Design

Weight- Bm ed Designs I03

for these ships has been drawn on the basis of the weight included in warship cost
sections 3, 4, 6 and 7 (see Fig. 4.14) which seems the nearest equivalent to
merchant ship outfit.
This frigate line and the line for trawlers both indicate an outfit ratio increasing
with length showing the same trend as that noted as applying to passenger ships
and presumably for the same reason.

4.4.2 More detailed outfit weight estimation - merchant ships

When the outfit weight is a significant proportion of the lightship weight, the
importance of accuracy in the outfit weight is emphasised and it is best to make a
more detailed weight estimate as early as possible in the design process.
As an intermediate step between calculating the whole outfit weight by the use
of the square number and a fully detailed calculation, the outfit weight can be
divided into a number of groups each of which can be proportioned on different
bases appropriate to its content. A possible subdivision might use four groups
related respectively to:
(i) structure,
(ii) cargo capacity,
(iii) accommodation area or complement,
(iv) deck machinery.
This concept is discussed in more detail in the next section.

4.4.3 Detailed outfit weight calculations - merchant ships
The desirability of dividing the outfit into a limited number of groups as a way to
improve approximate weight estimation suggested in the previous section would
in principle also be helpful in specification writing and in cost estimating although
unfortunately the ideal grouping for each of these purposes differs.
For specification writing the best grouping would be one that brought together
everything that is made by one shipyard department or one subcontractor.
For cost estimating it is desirable that the grouping should bring together items
whose cost per unit weight is similar whilst for both weight and cost it is essential
that there should be a parameter which provides a good measure for the group as a
whole and is reasonably easy to calculate.
In the past, shipyard trades were prominent amongst the outfit categories with
such items as smithwork, carpenterwork, sheet metal work, joinerwork, plumber-
work and electrical work. The first three of these have largely disappeared with
changes in ship design, but the other three remain.
For a modern rationale of outfit a division into the following four groups seems
sensible, although there are in each of the groupings some items which might