286 Dr. T. H. Havelock. [Apr. 1, 
For the model, Ship A, we have: Length = L = 400 feet; entrance = 
run = 80 feet. 
Hence, in this case we may take, in formula (17), / as approximately 
360 feet. We notice that this gives 7=09L; and in subsequent com- 
parisons, instead of leaving / to be adjusted to fit the experimental curve, 
we find there is sufficient agreement if we fix it beforehand as 0-9 of the 
length of the ship on the water-line. 
Compare, now, the length 7 with the ordinary “ wave-making length” of 
the ship; the latter is written as mL and is defined as the distance between 
the first regular bow crest and the first regular stern crest. From the present 
point of view (17) gives 
mL=1+}rx or m=09+4A/L, (18) 
where ) is the wave-length in feet of deep-sea waves of velocity v ft./sec. 
Calculating from this formula for Ship A, and writing V for velocity in knots 
(6080 feet per hour), we obtain Table ITI. 
We see that the statement that m lies between 1 and about 1:2 would 
hold for this ship if it were measured for ordinary speeds between about 
14 and 22 knots. 
Table III. 
vV | r m 
10 55°5 0:97 
14 110 1°03 
18 180 iL aly) 
22 270 1°24 
26 362 1°35 
30 500 1°35 
We proceed now to modify (14) by introducing into the second term a 
factor 1 — y cos(gl/v?). With 7 = 360, we find gi/v? is approximately 
4080/V*, with V in knots; further, from one value from the experimental 
curve we obtain y = 0:12. Thus for Ship A we have R in tons given by 
R = 4-5¢-2@83¥) 4.297 {10°12 cos (4080/V2)} 220, (19) 
Table IV shows some calculated values for R, and these are represented in 
fig. 4 by dots; the continuous curve is the experimental residuary resistance 
curve given by Froude, that is, the total resistance less the calculated 
frictional part. 
It is the custom to give the results of model experiments in the form 
of a fair curve, so that the positions of actual readings and the possible 
44 
