Page 156 - Practical Ship Design

Weight- Based Designs 123

x16 Fig. 6.1
x23 Figs. 6.3 and 7.4
x24 Figs. 7.5-9 and Table 7.4
x30 $6.7 and Table 6.1
x33,34,35 $6.9
In general, the sheet remains closely similar to the earlier version, but there are
notable differences which are worth some comment.
The column marked “first” design enables the designer to use either the
deadweightldisplacement ratio or the cargo capacityhull volume ratio to make an
initial assessment of hull dimensions using methods described in Chapter 3. This
involves making an initial guess of either the length or the block coefficient and
provision is made for a short iterative process until the calculated value of L ceases
to differ significantly from the input value.
In the third column the dimensions arrived at in the first column can be rounded
off before they are used in a second design iteration which follows the procedure
used in the earlier sheet.
The fourth column enables approximate calculations of the structural, outfit and
machinery weights to be made.
More detailed calculations of these weights can be made at a later stage using
the fifth and sixth columns. The layout of the outfit and machinery weight
calculations in these columns has been revised along the lines, and for the reasons
outlined in $4.4 approximations are included as well as the detailed calculations.
The powering calculations in the seventh and eighth columns has been modified
to permit the use of Cr’78 and the powers are all now in kilowatts. C,, values can
be obtained from Chapter 7, where the author’s reasons for preferring this pres-
entation is explained. C, values used can be either ITTC’57 or Grigson values and
(I + 0 values can be deduced values or figures derived using the Holtrop and
Mennen formula. (The format used for the spreadsheet was conditioned by the
constraint imposed to suit publication in this book.)
This spreadsheet has gone through several versions during its development but
has not had the lengthy practical use that its predecessors had. Users will probably
prefer to make some further changes, but should nevertheless find it a good starting
point.

4.7.2 Standard design sheet fur warships

A standard calculation sheet for the design of warships is given as Fig. 4.20. This
sheet which could readily be converted into a spreadsheet follows much the same
lines as the earlier merchant ship sheet, but uses warship weight groups. In one
respect it goes further than the merchant ship design sheet as it also includes a cost
estimating section.