Development of a four-bladed surface piercing propeller series

Abstract

The intent of this work was to develop a methodical series of four-bladed propellers of the surface piercing type so as to be able to design a surface piercing propeller for a given operating condition. A test rig along with instrumentation was developed at NSTL to determine the open water characteristics of surface piercing propellers experimentally. Initially, four model propellers were designed and manufactured with four different section shapes with the same pitch ratio and blade area ratio. The diameter of all the model propellers was fixed at 250mm. These propellers were of two basic section shapes: wedge and diamond back. To study the effect of trailing edge inclination (cup shape) three different wedge shapes were developed with the trailing edge making angles of 0°, 30°, and 60° to the horizontal respectively. These four propellers were tested extensively in the High Speed Towing Tank of NSTL. Weber number effects were found to be small in the model tests that were carried out at 20rps for the 250mm diameter propellers. The best performance at all immersions was obtained from SPP-3, the propeller having wedge shaped sections with the trailing edge inclined at 60° to the horizontal. The astern performance of this propeller was found to be satisfactory from the limited number of tests that were conducted.