Research of prevention measure for root cavitation erosion

For small high speed ships, which operate over 22 knots, cavitation phenomena called as root cavitation are happened easily on the root of propeller blades and boss, and then collapsed sequentially. Consequently, erosion can be happened at root area. This phenomenon is root cavitation erosion. Ship owners often regard the erosion as problem for safety side judging by that poor appearance. Accordingly, we need to suppress root cavitation erosion as small as possible. As the general prevention measures for the erosion, one or two holes called anti-cavitation hole are drilled on root of propeller blade to suppress the root cavitation erosion. Taking this measure, the root cavitation erosion can be somewhat suppressed but it cannot be completely prevented under severe operational condition. In this research, the original propeller with two anti-cavitation holes is machined additional anti-cavitation hole to reduce erosion. In order to compare the situations of root cavitation erosion of the propeller with three anti-cavitation holes and original propeller with two holes, full scale observation with actual ship equipped with these propellers were examined for 24 to 30 months. In addition, the effects of anti-cavitation holes are estimated by numerical calculations. As a result, it was confirmed that the drilling anti-cavitation holes can reduce the amount of root cavitation, and additional anti-cavitation holes can be effective measure for suppress the root cavitation erosion.