AN INVESTIGATION OF METHODS TO REDUCE OR ELIMINATE CAVITATION EROSION OF SHIP PROPELLERS BY DESIGN OPTIMIZATION AND PROTECTIVE COVERINGS

Effects of wake characteristics (angular width and magnitude of velocity defect) on the erosive nature of cavitation were investigated using a model propeller in water tunnel flows. Wake width appeared to control erosive impact intensity of the cavitation, as measured by the size and rate of formation of pits formed on the polished blades by impact of loads created by collapse of cavitation bubbles. Seven covering materials in combination with 13 primers and adhesives were evaluated in the laboratory. The limiting factors proved to be peel adhesion strength and hydrolytic stability of the covering/propeller bond. The best three polyurethane coverings were applied to a full-scale propeller (21-1/2 ft. dia.) Two of these systems gave encouraging results based on a propeller inspection after 10 months in service.