Page 59 - Practical Ship Design

30 Chapter 1

After quite a lot of thought, only ships whose displacements and drafts appear to
be in reasonable accord with one another as shown by a block coefficient calculation
based on the data given, have been included. This unfortunately necessitates the
omission of a number of quite important ships that would otherwise have been
included.
Some of the designs shown in Jane’s such as the British types 22 and 42, were
built in two batches of different lengths. The dimensional ratios LIB and LID of the
first batches could be assumed to represent the naval architect’s intent whilst the
later ships are ad-hoc modifications. On the other hand, it is just possible that the
lengths of the first batches were squeezed below their designer’s wishes by economic
constraints and the later versions are nearer to the designer’s preferred figures!
On the basis that approximate information is better than none, some of the
missing information for the ships for which data is given has been obtained by
scaling from the small-scale profiles.
Ten countries are represented as designers in Table 1.4 and it is interesting to
note that the dimension ratios calculated are remarkably similar and no national
trends can be identified.
Occasionally more and/or better dimensional and other information is given in
technical papers and in the present context of dimensions and their ratios, mention
must be made of a 1992 R.I.N.A. paper “On the variety of monohull warship
geometry” by W.J. Van Griethuysen, from which Table 1.5, which covers most
types of warships, is abstracted. The paper makes the point, well illustrated by the
figures, that different types of warships have quite distinctly different form
characteristics.

Table 1.5
Summary of warship dimension ratios (for volumetric Froude number, see $6.3, ix)

Type of warship V LIV’I’ LIB LID BID BIT Volumetric
( 10’ m‘) Froude no.

World War I1 battleship 40.6 7 7 14 1.8 2.5-3 0.8
Destroyer 2.3 8-9 IO 16 I .8 3-3.5 1.5
Minehunter 0.5 5-6.5 54 8 1.4 3.24 0.8
Corvette 1.2 7-8 7-8 II 1 .5 3.5 1.3
Frigate 3.5 7-8.5 8-9.5 13 1 .5 2.8-3.2 1.2
Cruiser 7.1 7-8.5 8-10 12 1.4 2.5-3.2 1.1
Aircraft carrier 13.9 67.5 6-8 9 I .3 3.34.1 0.8