82 A THEORY OF FLUID FRICTION. 
DISCUSSION. 
THE PRESIDENT :—This paper on “The Theory of Fluid Friction” is now open for dis- 
cussion. Is there any member who desires to discuss the paper? 
Mr. W. L. R. Emmet, Member of Council :—The subject of this paper is not exactly in 
my line, but I happen to have had an experience in connection with it that I think might be 
interesting to some members of this body. 
About twenty years ago Mr. H. W. Buck and I got the idea of building a toboggan 
boat, because we saw that in Schenectady we had a peculiarly good opportunity for trying 
one. We have about 21%%4 miles of absolutely straight track beside the Erie Canal, and we 
used it for experimenting with electric cars. 
We felt interested, and at our own expense built a boat about 25 feet long. We rigged 
up a powerful electric car, with a tow-line, a speed indicator on the action of the car, and a 
recording dynamometer on the tow-line of the boat. We loaded the boat to various loads 
and towed her at speeds from 1 to 31 miles an hour, and took records of the tow-line pull 
and speed. 
As I anticipated, the boat ceased to make waves when she reached a moderate speed, 
something like 15 miles an hour, and simply slid on the surface of the water without produc- 
ing a ripple. That indicated that the one thing which was resisting the boat was friction. 
The records taken seemed to indicate that the friction at these high speeds is quite different 
from that which the formulae given in books on naval architecture indicate. 
I attributed this to the fact that a great deal of air passed under the bottom of the boat, 
and I have heard among others the suggestion that air passing between water and the sur- 
face of the boat might make a large difference in the skin friction. I also know that that 
has been experimented with at low speeds and that the experiments have shown practically 
no apparent difference. 
From the curves which we took on our boat, I am rather inclined to think that at very 
high speeds, such as those which are considered in ships nowadays, the introduction of air 
might make a large difference. Of course the nature of the losses from friction must be 
due to the fact that a certain amount of water has imparted to it the motion of the vessel, 
and after receiving that motion, that it must lose it and convert it into heat. You can easily 
imagine in a large amount of air passing over a surface there might be such a foam pro- 
duced that the actual supply of water to the surface would be insufficient, and it would 
simply shear the foam, which might involve less friction than the actual contact with pure 
water. 
If we consider very high-speed vessels, it is easy to calculate that a very large amount 
of air could be put under them with a comparatively small expenditure of power, and, fur- 
thermore, that if the air were released under the vessel, the vessel would be bound to 
overrun it; it could not rise to the surface quick enough to avoid being overrun. 
I just mention this subject briefly, thinking some one interested might want to get such 
data, in which case they could use the same facilities, which are still there. 
Mr. F. B. Smitu, Member:—My comments are intended more to elaborate on the re- 
marks of Mr. Emmet than as a discussion of the paper. I think I brought up that subject 
myself several years ago, about the air under the boats having a great effect on their speed. 
