A SUBSTITUTE FOR THE ADMIRALTY FORMULA. 53 



placement, the proportions, dimensions, etc., and it is impossible to satisfactorily cover a 

 question involving so many variables when, as in the Admiralty formula, you select only 

 three — speed, displacement and power. Mr. Stevens has introduced the length, which is a 

 very essential factor as to the power required for a given speed, and in that way I am sure 

 he has made a distinct improvement. I think also it is an improvement to put the co- 

 efficient as the first power of the speed instead of as the indicated horse-power ; that reduces 

 the coefficient and makes less discrepancy between coefficients. The result, of course, is 

 really the same. 



As regards motor boats, I think Mr. Stevens is perfectly sound in using a semi-empirical 

 formula which does not follow the law of comparison. For such fast boats, as you increase 

 the displacement the resistance increases much more rapidly, and by the formula he chooses 

 he takes some account of that fact. I believe for the ordinary type of vessel it would be 

 more satisfactory to substitute for the square root of the length, the length itself, which re- 

 duces the formula again to one following the law of comparison. 



The Chairman : — When the idea is to interfere with a good old friend like the Ad- 

 miralty formula there sliould be some champions for it. Has it any friends at all ? We have 

 a family pride in having this son of one of our members bring out his first paper, and we 

 want to have good discussion upon it, if it is possible. 



Mr. E. H. Rigg, Member: — The Chairman asked if the Admiralty formula had not a 

 champion. Mr. Taylor gave me the hint; he compliments the Society upon the fact that 

 we have the son of one of our distinguished members presenting a paper. We must remem- 

 ber that the Admiralty formula was devised by our fathers long before naval architecture 

 enjoyed the facilities that this generation does, and before the days of high sea speeds and 

 experimental tanks ; it has served a most useful purpose. We recognize its limitations, how- 

 ever, so that it is gratifying to have an improvement, which extends and increases its use- 

 fulness. 



I would also like to draw your attention to the fact that Mr. Stevens makes use in his 

 paper of the ratio which Constructor Taylor uses in his Manual — I refer to the displacement- 

 length ratio. To my mind that constitutes a very important element in the accuracy of his 

 formula. Moreover, it is good to see everybody working along a unifonn line for technical 

 expressions: if you study literature on any one subject, you will find you have to look out 

 for expressions that are nearly the same thing, but not quite. It is gratifying that Mr. 

 Stevens follows up one of Mr. Taylor's expressions. 



The Chairman: — Are there any other remarks? Mr. Stevens, what has been said is 

 so complimentary that I do not know whether you care to say anything in reply, except to 

 express your thanks. However, you have the opportunity. 



Mr. Stevens : — I wish to express my thanks to both Naval Constructor Taylor and 

 Mr. Rigg for their remarks. This formula, as stated in the paper, was originated for the 

 rating of motor boats. About a year ago it occurred to me it might be used in place of the 

 Admiralty formula for calculating the speed of steamships, substituting the indicated horse- 

 power for rated horse-power, and tons displacement in place of cubic feet. After working on 



