Performance of Partially Submerged Propellers 



the transverse plane and the shaft-bending moments with a dynamometer 

 especially designed for this purpose. 



It is the objective of this paper to present the results of the experiments 

 on the four propellers and to make comparisons with their performance when 

 fully submerged, both cavitating and noncavitating. An analysis will be attempted, 

 albeit somewhat heuristically, of the hydromechanical sources of the force gen- 

 erated by partially submerged propellers so that guidance can be obtained for 

 future research, both theoretical and experimental. There will be many questions 

 raised which at this point are incompletely answered. It is hoped that these ques- 

 tions will stimulate other investigators into examining this form of propulsion, 

 which holds potential for the efficient propulsion of high-speed vehicles. 



EXPERIMENTAL PROCEDURES 



The objective of the initial set of experiments was to determine the efficiency 

 and thrust characteristic of partially submerged supercavitating propellers and 

 to compare these with the fully submerged performance. 



For this phase three propellers were used from the NSRDC super cavitating- 

 propeller library, Propellers 4002, 3820, and 3767. Table 1 lists the character- 

 istic coefficients for these propellers. Figures 4-6 show the geometry and 

 photographs of the three propellers. As may be noted, only the camber shape of 

 the sections was common to all three propellers. All of the sections had blunt 

 trailing edges, except the tip 20% of Propeller 3767. The primary differences 

 sought in selecting these propellers were number of blades and pitch ratio. 



Measurements of thrust, torque, and rpm were made in open water at two 

 submergences, semisubmerged, and with the shaft centerline 2 in. above the 



Table 1 

 Propeller Characteristics 



''Propellers 3768 and 3767 are different-sized models of the same pro- 

 peller. 



1455 



