{RANSACTIONS Of SECTION G, 849 
it is equally true that in many ways the trials of small swift vessels constitute 
model experiments from which interesting information may be obtained as to what 
would be involved in driving ships of large size at speeds much exceeding any of 
which we have experience. When the progressive steam-trials of such small 
vessels can be studied side by side with experiments made on models to determine 
their resistance at various speeds, then the fullest information is obtained and the 
best guide to progress secured. This advantage, as has been said, we owe to 
William Froude. 
His contributions to the Reports of the British Association are classics in’the 
literature of the resistance and propulsion of ships. In 1874 he practically 
exhausted the subject of frictional resistance so far as it is known; and his 
Presidential Address to this Section in 1875 dealt fully and lucidly with the 
modern or stream-line theory of resistance. No doubt there would be advantage 
in extending Froude’s experiments on frictional resistance to greater lengths and 
to ship-shaped forms. It is probable also that dynamometric determinations of the 
resistance experienced by ships of modern forms and considerable size when towed 
at various speeds would be of value if they could be conducted. These extensions 
of what Froude accomplished are not easily carried out; and in this country the 
pressure of work on shipbuilding for the Royal Navy has, for many years past, 
taxed to the utmost limits the capacity of the Admiralty experimental establish- 
ment so ably superintended by Mr. R. EH. Froude, allowing little scope for purely 
scientific investigations, and making it difficult to deal with the numerous experi- 
ments incidental to the designs of actual ships. Now that Holland, Russia, Italy, 
and the United States have equipped experimental establishments, while Germany 
and France are taking steps in that direction, we may hope for extensions of purely 
scientific work and additions to our knowledge. In this direction, however, I am 
bound to say that much might be done if experimental establishments capable of 
dealing with questions of a general nature relating to resistance and propulsion 
were added to the equipment of some of our universities and colleges. Engineer- 
ing laboratories have been multiplied, but there is as yet no example of a model 
experimental tank, devoted to instruction and research. 
It is impossible, and possibly is unnecessary, to attempt in this Address any 
account of Froude’s ‘scale of comparison’ between ships and models at ‘ correspond- 
ing speeds.’ But it may be of interest to give a few illustrations of the working 
of this method, in the form of a contrast between a destroyer of 300 tons, 212 feet 
long, capable of steaming 30 knots an hour, and a vessel of similar form enlarged 
to 765 feet in length and 14,100 tons. The ratio of dimensions is here about 
3°61: 1; the ratio of displacements is 47 : 1; and the ratio of corresponding speeds 
is 1:9: 1. 
To 12 kmots in the small vessel would correspond 22:8 knots in the large 
vessel ; and the resistance experienced by the large vessel at 22'8 knots (neglecting 
a correction for friction) should be forty-seven times that of the small vessel at 
12 knots. By experiment, this resistance for the small vessel was found to be 
18 tons. Hence, for the large vessel at 22°8 knots the resistance should be 
84'6 tons. This would correspond to an ‘ effective horse-power’ of over 13,000, or 
to about 26,000 indicated horse-power. The frictional correction would reduce 
this to about 25,000 horse-power, or about 1:8 horse-power per ton. Now turning 
to the destroyer, it is found experimentally that at 22°8 knots she experiences a 
resistance of about 11 tons, corresponding to an effective horse-power of over 
1,700, and an indicated horse-power of about 3,000: say 10 horse-power per ton, 
or nearly five and a half times the power per ton required in the larger vessel. 
This illustrates tae economy of propulsion arising from increased dimensions, 
Applying the same process to a speed of 30 knots in the large ship, the corre- 
sponding speed in the small ship is 15°8 knots. Her resistance at that speed is 
experimentally determined to be 3'5 tons, and the resistance of the large ship at 
30 knots (neglecting frictional correction) is about 165 tons. The effective horse- 
power of the large ship at 30 knots is, therefore, about 34,000, corresponding 
to 68,090 horse-power indicated. Allowing for the frictional correction, this would 
drop to about 62,000 horse-power, or 44 horse-power per ton. Vor the destroyer 
1899 31 
