ANALYSIS OP TEST DATA ON THE PERFORMANCE CHARACTERISTICS OP PLANING 

 AND DISPLACEMENT FLOATS FOR SUPPORTING SUBMERGED LOADS 



ABSTRACT 



Data on the performance characteristics of a planing float and of a 

 displacement float, originally designed for supporting a catenary loop of 

 minesweeping cable, are analyzed. The planing float was a prototype of the 

 TMB planing float and was constructed of welded steel. The displacement 

 float was in the form of a body of revolution and was constructed of balsa 

 wood. 



The data on the planing float in the planing regime are compiled 

 Into a single nondimensional relationship between drag, total load, and speed- 

 length ratio. The characteristics of the balsa -wood displacement float are 

 also presented in nondimensional form as a family of curves of drag coeffi- 

 cient plotted on speed-length ratio with a load coefficient as parameter. 



A region of instability was shown to exist in the transition from 

 subsurface to surface operation of the TMB planing float, and a hysteresis 

 loop in the drag characteristics of this float was discovered. It was also 

 found that this float, as well as the displacement float, exhibits the same 

 type of striatlons in the flow over the float when towed near the water sur- 

 face, just before complete emergence, as is shown by spheres and projectiles 

 dropped through an air-water interface. A hypothesis based on the instabil- 

 ity of the vortex formed near the point of separation is offered as a more 

 adequate explanation of this phenomenon than the idea of cavitation formation 

 about minute nuclei on or near the surface of the specimen. 



A displacement float submitted by the Naval Mine Warfare Test 

 Station was also tested, but no analysis of the data was made since the tests 

 showed that the float was not useful for supporting submerged loads. The 

 tests of the Naval Mine Warfare Test Station float are reported in an appen- 

 dix. Observations of the performance of this float and of the TMB planing 

 float towed in a seaway are discussed. Pressure tests to determine the maxi- 

 mum depth of submergence of the steel planing float before complete collapse, 

 and problems in the construction and waterproofing of the balsa-wood float 

 are also considered in appendixes. 



INTRODUCTION 



In November 19^3 the David Taylor Model Basin was requested (1)* to 

 undertake the design and development of floats for supporting submerged loads. 



* Numbers in parentheses indicate references on page 44 of this report. 



