Page 200 - Introduction to Naval Architecture

186 RESISTANCE

Table 8,1 R. E. Froude's skin friction constants./values (metric units): frictional
resistance = /SV - l mTy , newtons; wetted surface, 5, in metres; ship speed, V, in m/s.
Values are for salt water. Values in fresh water may be obtained by multiplying by
0.975

length f length 1 length 1
(m) (m) (m)

2 1.966 18 1.526 70 1.441
3 1.867 20 1.515 80 1.437
4 1.791 22 1.506 90 1.432
5 1.736 24 1.499 100 1.428
6 1.696 26 1.492 120 1.421
7 1.667 28 1.487 140 1.415
8 1.643 30 1.482 160 1.410
9 1.622 35 1.472 180 1.404
10 1.604 40 1.464 200 1.399'
12 1.577 45 1.459 250 1.389
14 1.556 50 1.454 300 1.380
16 1.539 60 1.447 350 1.373

Alternative formulations of frictional resistance
Dimensional analysis suggests that the resistance can be expressed as:

Later approaches to the resistance of ships have used this type of
formula. The function of Reynolds' number has still to be determined
4
by experiment. Schoenherr developed a formula, based on all the
available experimental data, in the form:

from which Figure 8.7 is plotted.
5
In 1957 the International Towing Tank Conference (ITTC) adopted
a model-ship correlation line, based on:

The term correlation line was used deliberately in recognition of the
fact that the extrapolation from model to full scale is not governed
solely by the variation in skin friction. Q values from Schoenherr and
the ITTC line are compared in Figure 8.8 and Table 8.2.