A method for carrying out of cavitation - tests on ship's propellers

摘要

A technique for testing marine propellers by analyzing the type of cavitation appearing on a reduced-scale model of the associated actual ship, and thereby obtaining data for correcting imperfections in propeller design, and for reducing pressure fluctuations at the lower sternframe portion of the ship. The technique inculdes simulating the water flow acting on the propeller. The procedure is characterized by adjusting the denominator of the cavitation index of the model in order to achieve an approach in the tests to equality between the cavitation indices of the model and the actual ship. This adjustment is achieved in the tests by increasing the towing speed or the propeller revolution rate of the model until the above-mentioned equality of cavitation indices is reached, ignoring the influence that the actual component of the wake speed due to wave formation might have in the tests. The procedure includes consideration of the increase in pressure of the propeller disc points due to the increased draught caused by the wave formation, and establishing a water line for the model corresponding to the loading condition to be tested, by the use of a steel sheet, or the like, on the hull of the model of adequate thickness and dimensions. The procedure enables tests to be conducted in conventional ship model basins without requiring vacuum, or in open water with the model in the loading condition desired, either floating on the surface or, made watertight and being totally submerged, taking into consideration the immersion of the model when the numerator of the above-mentioned cavitation index is calculated, and the tests being conducted at the speed for which the cavitation indices of the model and actual ship are equalized, the dimensional thrust coefficient KT of the model being identical to that of the actual ship.