Page 236 - Practical Ship Design

198 Chapter 7

0.00 0.10 0.20 0.30
2
P = (Cb)”3 . SA

Fig. 7.5. (1 + K) values for use with Grigson friction line.

7.1.5 Corrections for differences in hull geometry

All the C,, values so far obtained relate to a geosim of the basis ship and further
corrections must be made for any departures from this geometry.
Although the use of the basis ship data must presuppose that the Cb value and the
LCB position of the new design differ to only a minor extent from the values of the
basis ship, corrections should be made for the effect of these features if they differ.
A correction for a difference in Cb can be made by using the ratio of the C, values
given for the two block coefficient values on one of the graphs given in this
section.
There is less data available to assist in making a correction for a change in LCB
position but Guldhammer and Harvald’s data and some of Moor’s data can be used
- again in the form of a ratio.
Corrections for a change in L/B and/or the LIT ratio can be made using the
Mumford indices given in 56.7.