Page 243 - Practical Ship Design

Powering II 205

66

6.4
6.2
6.0

5.8
5.6

54
’a 5.2
.r
X
o’ 50
4.8

46
4.4

4.2
40

38
3.6
0.45 0.50 0.55 060 0.65
Cb

Fig. 7.9. Powering of twin screw ships. Moor’s optimum. Model L = 5 m, LIB = 7.28, TIL = 0.045.

For merchant ships C, = 0.935 + 0.05 C,
For frigates and similar vessels C, = 0.58 + 0.4 C,
Figure 7.10 presents some data from warship tank tests, sticking to block coefficient
as the base. The data is again corrected to a standard model length of 5 m but in this
case LIB is set at 8.71 and TIL at 0.035 as more representative of warships than the
proportions used for twin screw merchant ships.

7.2.5 Calculation of C,,
The calculation of C,, from C,, starts with the calculation of C,, and of (1 + K)
using whichever friction line and associated (1 + K) formula is preferred and a
spreadsheet similar to Fig. 7.2.