Page 206 - Practical Ship Design

172 Chapter 6

cating the use of the form factor. These annotations are essential if the
correct ship-model correlation factor is to be chosen;
(vi) finally there is the fact that the units in which the data of some of the earlier
methods is recorded date back to before the general adoption of SI units.
Altogether, the use of older methods can present a number of pitfalls to those to
whom this is unfamiliar territory. Nevertheless, brief descriptions of two of the
best known methods, Taylor and Ayre, are included in this chapter as it is thought
that some lessons can be learnt from these, and occasionally when a designer has
no better data available one of these methods may still be useful.
More modern methods are outlined in succeeding sections, which are arranged
in historical order and reflect the technology of their dates of origin.
$6.7 Moor’s method uses iC, Froude
56.8 Guldhammer and Harvald’s method uses C, ITTC’57
06.9 Holtrop and Mennen’s method uses C, ITTC’78
$7.1 The use of in-house data
$7.2 Moor’s data converted to model size for use with C,’57, C,’78 or
Grigson friction lines.

Whilst the later methods may be the best in theory there is no doubt that there is
more data available in some of the earlier forms and provided the appropriate
ship/model correlation factors are used these can still give reasonably accurate
results. But it is essential the testing used trip wires.

6.5 TAYLOR’S METHOD

This method was originally presented in a book entitled Speed and Power of Ships
published in 1910 by Rear Admiral D.W. Taylor of the U.S. Navy. The book,
which was revised in 1933 and 1943, was for a long time the best known work on
ship powering.
The residuary resistance, which consists of all resistance other than the skin
frictional resistance is obtained from graphs of Rr/A. Taylor plots values of this, for
two values of B/T (2.25 and 3.75) and a range of values of V/& (from 0.30 to 2.0)
against parameters of prismatic coefficient from 0.48 to 0.86 and displacement/
length ratio from 20 to 250.

A
where displacement/length = 6.34
[LI 1001~