34 



The shape of the curve drawn through the data on Figure 27 was 

 verified by comparison with a plot made on a similar basis of data available 

 from tests under constant load of a number of high-speed planing boats. The 

 mean curve through the data of Figure 27 can be closely approximated by the 

 equation 



^ X 10« = 0.5l(^/ - 9.15(^f -H 52.0(^f [12] 



when Cl ^ O.69. 



In the actual design of a TMB float, therefore, the characteristics 

 of a given float can be determined by first determining the regime in which 

 the float will operate. This can be done by determining the value of C^. If 

 C^ is greater than O.69, the methods of Reference (2) should be used. If Q 

 is equal to or less than O.69, the characteristics can be determined from Fig- 

 ure 27 or Equation [12]. 



PERFORMANCE CHARACTERISTICS OF THE TMB DISPLACEMENT FLOAT 



The development of the displacement float as an alternate to the 

 planing float was dictated by a particular specification of the material to 

 be used in its construction. Since the most practicable shape for a balsa- 

 wood float was considered to be a body of revolution, the alternate float 

 necessarily is of the displacement type. 



Unlike the TMB planing float, which develops dynamic lift through 

 planing action, the TMB displacement float derives its load-carrying capacity 

 almost wholly from the hydrostatic forces on the float. As a result, the 

 total load on this float should never be allowed to exceed its reserve buoy- 

 ancy. The planing float, on the other hand, can carry loads which increase 

 with towing speed provided that the dynamic lift on the float increases at 

 least as fast as the imposed load. 



Before presenting the techniques and results of the tests and the 

 method finally used in the analysis of the displacement-float data, the de- 

 sign features of this float and the reasons for their selection are discussed. 



DESIGN OF THE TMB DISPLACEMENT FLOAT 



The displacement float designed for the catenary-sweep application 

 was based on the design of the "O" type mlnesweeping float (9). However, 

 the TMB float has a higher aspect ratio (or diameter-to-length ratio), which 

 necessitates relatively larger tail surfaces than those on the "O" float in 

 order to provide control area outside the wake of the hull. 



