64 SOME MODEL, BASIN INVESTIGATIONS OF THE INFLUENCE 
of Figs. 36 to 41, Plates 15 to 20, could be slightly improved by using full 
after water-lines—the V stern. 
In the case of Series No. 32, the region of minimum residuary resistance 
for low speeds is not so well defined and appears to correspond to a smaller 
bow water-line coefficient than in the case of Series No. 29. It should be 
remembered, however, that in Series No. 32, the stern water-line coefficient 
is ten points greater than the bow coefficient; while in Series No. 29 it is 
but five points greater. In each case, as we pass beyond the region of 
critical speed length ratio, say from 0.85 to 0.9 there is a marked change in 
V : nae : : 
the contours. For ip for instance, the minimum residuary resistance 
corresponds to the fullest ended curves of sectional areas while the corre- 
sponding bow water-line coefficient falls off materially. 
In other words, for the minimum resistance at the high speeds we need 
to materially fine the ship at the water-line and fill it out below water. The 
broad conclusion to be drawn from the results I have laid before you are 
confirmed by other experiments which agree in indicating that the type of 
form suitable for low and moderate speed length ratio below 0.9 is not at all 
adapted for high speed length ratios of 1 and above. 
The reason is I think to be sought in the relative dimensions of the ships 
and the waves which it makes. At the low speeds only the ends of the ship 
and more particularly the forward end materially affect the resulting waves, 
which, after all, are small and offer but comparatively small resistance. At 
the high speeds, however, the whole fore-body has to do with the creation of 
the waves, and we decrease resistance by making the water-line as fine as 
possible and putting as much as possible of the displacement well below 
water where the pressures due to its thrusting itself into the undisturbed 
water will be as much as possible absorbed in doing the necessary pumping 
aft of the water and not in raising the surface into waves. 
Let us attempt now to gain some idea as to the quantitative effects in 
actual cases of the variation of form we have been considering. Consider 
the moderate speeds first. Say Figs. 37 and 42, Plates 16 and 21, where the 
speed length coefficient is 0.8. 
In Fig. 37, Plate 16, the minimum residuary resistance indicated in 
pounds per ton is 1.4 and while the possible variations in water-line curves 
of sectional area are somewhat a matter of opinion it seems reasonable to 
say that without a guide we might adopt coefficients and curves which would 
give us a residuary resistance as high as 1.8 pounds per ton. 
The possible gain then would be about 0.4 of a pound per ton which is 
