Cavitation erosion tests of marine coatings in model scale

Abstract

Rudders of large container ships are easily affected by cavitation that is well known to be induced by significant axial flows behind a propeller and discontinuities in the rudder. Many shipbuilding companies and ship owners are searching for methods to prevent or reduce the cavitation erosion occurred in the rudder. Among several methods, coating method is getting much attention because it can be adopted easily and chiefly. In this point of view, reliable and appropriate erosion tests are required in the stage of initial estimation on the marine coating. To conduct erosion test properly, the simulation of heavily erosive cavitation is necessary. The very erosive cavitation can be simulated by an inclined propeller dynamometer in the medium-size cavitation tunnel of MOERI. The inclined shaft for propeller makes strong cavitaion, which occurs around the root of a propeller blade. The cavitation begins at the leading edge of the propeller and contracted toward the trailing edge through the re-entrant jet action. The cavity focused on the region near the trailing edge collapsed over the blade surface. The impact pressure by the cavitation collapsing is enough damage the blade surface in the form of pit. This cavitation impacts created by the collapsing process are very severe and are different from those by other erosion test methods. The newly developed cavitation erosion test method is successfully employed to evaluate the marine coatings mainly composed of epoxy elastomer or silicone polymer material. ？ 2010 by The International Society of Offshore and Polar Engineers (ISOPE).