15 



Towing Spsed, 0.5 Kaet 



TewlBf ipe@d, 4.5 Knats 



Towing Speed, 6.0 Knots Towing Speed, 9-0 Knots 



Figure 12 - Photographs of TMB 4l-lnch Planing Float Being Towed 



These tests were made under loads imposed by the 25-pound weight towed from the forward towpolnt. 



due to planing action. Under higher loads, however, the pressure reduction 

 on the bottom surfaces was sufficient to submerge the float completely. 



As the float becomes submerged, it begins to develop dynamic lift 

 as a hydrofoil of low aspect ratio. Based on systematic tests of various 

 hydrofoils at several depths of submergence (6), the dynamic lift on the 

 float may be expected to show an increase up to a depth of about 5 chord 

 lengths, at which depth the lift is fully developed to its maximum value. 

 The maximum lift is then given by Equation [3], page 1, as determined from 

 tests previously reported. In the tests considered here, the load on the 

 float remained within definite limits as the speed was increased. As a re- 

 sult, the float assumed an equilibrium position below the water surface at 

 each speed, until, with increasing speed, it developed sufficient lift as a 

 hydrofoil to return to the surface. 



