On Performance of Propellers with Cutted Tips

Abstract

Performance of propellers with the tips cutted for shortening their diameters has been studied by open water test in Mejiro Tank. In self propulsion tests, cutting the tips of propeller usually decreases model ship's speed and increases propeller's revolution compared to original condition at same DHP. We studied this problem giving our mind to the case of change of main engine of ships. So, we had the following tests: Test 1. Influence of cutting tips; Adopted rate of diameter decrease is -10% and -20%, and fairing ranges from 0.8 to 1.0 of the diameter of each cutted propeller. Test 2. Influence of fairing range; 0% (no fairing), 0.1R, 0.2R and 0.3R fairing ranges are tested, rate of diameter decrease being 15% for each. Model propeller particulars are shown in Tables 1 and 2. Fig. 5 shows the variations of propeller revolution and ship's speed at constant DHP, analyzed from open water test results, considering the change of advance coefficient (1-w) according to the changing of diameter. From this analysis, we find first that the variation of propeller revolution derived from test is smaller than estimated value from series chart, and next that the wider the fairing range is, the larger the increase of revolution is, but the width of the fairing range has practically no influence of the propeller efficiency.