MODEL EXPERIMENTS AND SPEED TRIALS OF 60-FOOT MOTOR 



CRUISER KATHMAR II. 



By a. E. Luders, 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.] 



Having been able to make a great deal of use of the various papers on the 

 subject of resistance of ships and models read before this Society, it has occurred 

 to the writer that possibly similar data of a type of vessel that has not been 

 touched upon in previous papers may prove of interest. 



For this purpose Robert T. Fowler, Esq., the owner of the 6o-foot gasoline 

 cruiser, Kathmar II, kindly placed this boat at my disposal and a number of 

 runs, results of which are plotted on a curve sheet, were made. To supplement 

 this practical information the Navy Department most courteously agreed to make 

 and test a model of this boat under similar conditions of draught, their interest 

 making this paper possible. 



The results of the model experiments as made by them are given on the same 

 plate as the other information. 



The trials were over the New York Yacht Club Course, i.i knots at Hemp- 

 stead Bay, where four double runs were made. 



Kathmar II was launched in the spring of 191 1, at which time she floated — in 

 light cruising trim — at her designed load water line. The difference of displace- 

 ment on the 191 3 trials is accounted for by the boat being deeply laden, prepara- 

 tory to starting on an extended course, by soakage and the gradual augmenting 

 of equipment, etc., that occurs from season to season. 



The bottom of this boat had not been painted for three weeks and was un- 

 doubtedly soft, though not foul. This probably explains somewhat the increase 

 in horse-power over model experiments by an amount that indicates that the actual 

 skin friction was practically double the theoretical. 



The increased, horse- power required to drive the boat with the stern cut off 

 square at the waterline was unexpected. 



The effective horse-power from trial was deduced from the thrust of the pro- 

 peller (the wheel being deeply immersed, only 3 per cent of wake was assumed), 

 and using results of Professor Durand's investigation (Vol. 4) as a basis from 

 which to work by the laws of comparison of similar propellers. On the basis of 

 a propulsive coefficient of 65 per cent the horse-power at the 10.26-knot point 

 agrees well with the brake test of the motor. 



In general, the design of Kathmar II proved very satisfactory in seaworthi- 

 ness and stability, and was somewhat faster than similar boats of the same power. 



