PERFORMANCE OF PARTIALLY 

 SUBMERGED PROPELLERS 



J. B. Hadler and R. Hecker 



Naval Ship Research and Development Center 



Washington, D. C. 



ABSTRACT 



Open-water experiments have been conducted on Z three -bladed and 1 

 two-bladed super cavitating propellers operating in the partially sub- 

 merged condition. Thrust, torque, and rpm have been measured over a 

 wide range of advance ratios. The results have been compared with 

 existing experiments made with the propellers fully submerged, both 

 cavitating and noncavitating. A geosim of one of the three -bladed pro- 

 pellers has been further tested over a wide range of advance ratios at 

 various speeds of advance. Besides the thrust, torque, and rpm, the 

 vertical and horizontal components of the transverse forces have been 

 measured as well as the location of the center of thrust. The latter 

 measurements have been made with a four -component dynamometer 

 that measures the bending moments imposed by the propeller. 



The results have been analyzed to ascertain the hydrodynamic origin of 

 the various forces and how they change with different advance ratios 

 and different speeds of advance. Through this analysis, identification of 

 major problem areas is attempted with the hope that viable research 

 goals can be established. 



HISTORICAL BACKGROUND 



Since the 1850' s, the screw propeller has been the dominant form of marine 

 propulsion. Its advantages over the paddle wheel, which it replaced, were its 

 light weight, its relatively high rotative speed, and its insensitivity to change in 

 submergence. As a consequence of its success, much inventive and research 

 effort has gone into improving performance or devising specialized applications, 

 using the screw-propeller principle. One of the specialized offshoots was the 

 partially submerged propeller. Initially, this propeller was viewed as another 

 means besides the paddle wheel for achieving shallow-draft propulsion in shel- 

 tered waters. The first U.S. patent was issued about one hundred years ago 

 (1869) to C. Sharp of Philadelphia (Pa.). His patent was quite ingenious, in that 

 he yawed the propeller to the flow to reduce the transverse force, used multi- 

 blades to reduce unsteady forces, cupped or, in current terminology, cambered 

 the blades to improve their effectiveness, and used high pitch for maximum ef- 

 ficiency. Figure 1 shows some of the sketches contained in his patent grant. 



As engine developments progressed and higher boat speeds became practi- 

 cal, the emphasis as shown by the patents shifted from low-speed shallow-draft 



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