A SUBSTITUTE FOR THE ADMIRALTY FORMULA. 

 By E. a. Stevens, Jr., Esq., Member. 



[Read at the twenty-first general meeting of the Society of Naval Architects and Marine Engineers, held in 



New York, December 11 and 12, 1913.] 



During the winter of 1906- 1907 the writer served on a subcommittee of the 

 Jamestown Motor Boat Committee, known as the Rules Committee, whose duty 

 it was to formulate a rule for the rating of motor boats that were to participate in 

 the races to be held during the Jamestown Exhibition. 



At the suggestion of Mr. M. M. Whitaker it was decided to use a formula that 

 would rate boats according to a speed determined from easily ascertained hull 

 measurements, and rated power of their motors. This formula had to be of com- 

 paratively easy application, and involve no laborious calculations. 



After some discussion the following formula was adopted : — 



in which V was the speed in nautical miles per hour ; P the rated power ; L the water- 

 line length; D the displacement in cubic feet, and C a constant which for racers 

 was 1 1 and cruisers 9.7. 



The proposed races at the Jamestown Exhibition were not held, but this for- 

 mula was used by the Motor Boat Club of America during its regatta of 1907. It 

 worked out fairly well, but not to the satisfaction of all the owners whose boats took 

 part in the races; it was, however, an improvement on the formula of the Amer- 

 ican Power Boat Association which was used the year before, where in some cases 

 the scratch boat had to make an impossible speed in order to win. 



DERIVATION OF THE FORMULA. 



This formula was derived from the well known Admiralty formula as fol- 

 lows: — 



LH.P.^^lAZ: or K=^^-H-P;XC 



C jj,. 



Now Z?^= = 



As the length of vessels of similar models varies as D^ length (or L) was 

 substituted for this factor, which gives 



,t_ D' 



Z>' = 



Vz 



