floats for catenary sweeps were constructed of 0.072-inch sheet steel with a 

 3/8-inch steel plate as trimming ballast at the stern. These floats are 4l 

 inches long and weigh 5^-9 pounds in air, with a reserve buoyancy of 9^ pounds 

 per float . 



The possibility of submergence of a float during service had to be 

 considered, and the structural strength needed to meet this contingency had 

 to be provided. The use of bulkheads inside the float was impracticable be- 

 cause of the resulting increase in weight and the reduction of reserve buoy- 

 ancy. For these reasons, it was decided to use a hollow float reinforced by 

 thin rods and prestressed by internal air pressure. The details of the con- 

 struction and the results of tests to determine the maximum allowable depth 

 of submergence are discussed in Appendix 5 ■ 



SUMMARY OP PREVIOUS DATA AVAILABLE FOR THE TMB 

 PLANING FLOAT AND PURPOSE OF PRESENT TESTS 



The results of previous tests to determine the load-carrying char- 

 acteristics of the TMB planing float are reported in Reference (2). These 

 tests were designed to provide data for maximum loading conditions. As a 

 result, the float was tested under loads that are much greater than those 

 encountered in the usual applications of planing surfaces. Under light loads 

 at any speed or with moderate loads at high speeds, the float develops suffi- 

 cient dynamic lift due to the fluid reaction on the bottom surfaces to allow 

 full planing action with no contribution from the reserve buoyancy. 



Under large loads, the float submerges slightly so that a sheet of 

 water flows over the top. This condition induces dynamic lift as on a sym- 

 metrical airfoil, in addition to the reserve buoyancy. Under these conditions 

 the lift-drag ratio, including the lift due to buoyancy, was found to be 3-0; 

 the average trim angle was about 15 degrees. The tests showed that the float 

 was able to carry a load of 0.625^6* in addition to its own weight W. Here 

 q = ^pv^, p is the mass density of the fluid in slugs per cubic foot, v is 

 the towing speed in feet per second, and 6 is the beam of the float in feet. 

 Thus the safe maximum lifting capacity L of the TMB float when operating as 

 a surface buoy is given by 



L = 0.625(/6' +W [1] 



The float was also tested as a fully submerged hydrofoil. In this 

 condition the trim angle, or angle of attack, was found to be 28.5 degrees, 

 and the drag D was given by 



D = 0.83?*" [2] 



