Page 206 - Introduction to Naval Architecture

192 RESISTANCE

Table 8.4 R. E. Froude's frictional data, O and /values. Frictional resistance =
/$V l 825 Ibf. Values are for a standard temperature of 15°C, /values are for salt water
2
with Sin ft , V'm knots. Values of/in fresh water may be obtained by multiplying by
0.975.
Length O 1 length O '
(ft) (ft)

5 0.15485 0.012585 80 0.08987 0.009309
10 0.13409 0.011579 90 0.08840 0.009252
15 0.12210 0.010925 100 0.08716 0.009207
20 0.11470 0.010524 200 0.08012 0.008992
25 0.10976 0.010269 300 0.07655 0.008902
30 0.10590 0.010068 400 0.07406 0.008832
35 0.10282 0.009908 500 0.07217 0.008776
40 0.10043 0.009791 600 0.07062 0,008726
45 0.09839 0.009691 700 0.06931 0.008680
50 0.09664 0.009607 800 0.06818 0.008639
60 0.09380 0.009475 1000 0.06636 0,008574
70 0.09164 0.009382 1200 0.06493 0.008524

175
Table 8.5 (Z)-°- values
© @-0.175 © ©-«•"*

0.05 1.6892 1.00 1.0000
0.1.0 1.4962 1.20 0.9686
0.15 1.3937 1.40 0.9428
0.20 1.3253 1.60 0.9210
0.30 1.2345 1.80 0.9023
0.40 1.1739 2.00 0.8858
0,50 1.1290 2.20 0.871 1
0.60 1.0935 2.40 0.8580
0.70 1.0644 2.60 0.8460
0.80 1.0398 2.80 0.8351
0,90 1.0186 3.00 0.8251

The method of extrapolating to the ship from the model is illustrated
diagrammatically in Figure 8.9. It will be noted that if the friction lines
used are displaced vertically but remain parallel, there will be no
difference in the value of total resistance calculated for the ship. That
is the actual frictional resistance taken is not critical as long as the error
is the same for model and ship and all the elements making up the
residuary resistance obey the Froude law of comparison. It is the slope
of the skin friction line that is most important.