41 



towpolnt, the effect is less marked and an actual minimum does not occur in 

 the drag curve. For the lightest loading condition, under which the float 

 remained unsubraerged throughout the entire speed range, the drag curve shows 

 the form characteristic of the resistance of surface vessels. At the high- 

 er speeds, the drag of the float is higher under the lightest loads than 

 under heavier loads. This is a direct result of the fact that the float 

 remained on the surface under this condition, whereas it did not return to 

 surface operation under the other loadings. Comparison of the curves of 

 Figure 30 with the photographs of Figures 3T through 3^ shows clearly the 

 correlation between the resistance curves and the performance of the float 

 at the various speeds and loads . 



In order to put these data into a form more useful for design pur- 

 poses, it is possible to describe the drag of the float in terms of a non- 

 dimensional drag coefficient C^ as a function of a load or displacement 

 , coefficient C^ and the speed-length ratio V/Vd. Since the coefficient of 

 frictlonal resistance will remain roughly a constant over the range of Rey- 

 nolds numbers in which this design is likely to be used, and for the reasons 

 outlined above, dependence on Reynolds number may be neglected. As a result, 

 the drag characteristics may be written in the functional relationship 



where 



and 



c,, = Q,(c„-^) [13: 





where D is the drag of the float in pounds, 



p is the mass density of the fluid in slugs per cubic foot, 

 V is the speed in knots, 



d is the maximum diameter of the float in feet, 

 w is the weight of the fluid in pounds per cubic foot, and 

 A is the total load on the float, including the weight of the float it- 

 self, in pounds. 



The data of Figure 30 reduced to nondimensional form are shown in 

 Figure 35 as a plot of Cp on a basis of V/Vd, with C^ as a parameter. The 

 values of the load coefficient represent means of the values actually derived 

 from the loading conditions at each spot. The maximum deviation of the actu- 

 al coefficient at each spot from the value shown on the corresponding curve 



