Open Water Tests with 4-Bladed Propellers

Abstract

Results of experiments in open water at the Teishinsho Ship Experiment Tank are presented for 4-bladed propeller series, designed mainly for single-screw mercantile work. Three series of propeller were tested, namely, propellers with increasing pitch, decreasing pitch and constant pitch, all other particulars remained the same.The general plan of propeller is presented in Fig. 1. All the propeller models had diameter of 0.22m, boss ratio of 0.25, expanded area ratio of 0.40, blade thickness ratio of 0.045 and aerofoil-shaped blade sections. Six pitch ratios were taken for each series, namely, 0.4, 0.6, 0 8, 1.0, 1.2 and 1.4.The tests were carried out by means of a propeller boat with built-in propeller dynamometer. The immersion of the centre of propeller shaft was equal to 0.9D. The number of revolutions was kept constant at 7.0 per sec, and the speed of advance varied. The measured results were corrected for the static pressure of water on the shaft section, the resistance of the propeller boss and for the shaft frictional loss.No-dimensional diagrams of the test results are given in Fig. 2. From these diagrams, the design diagrams for our three series of propeller were constructed according to Admiral Taylor's method, and are given in Figs. 35. Also the design diagram similar to Dr. Schmidt's form is given in Fig. 6 for the constant pitch series.From Fig. 2 and Figs. 35, it can be seen that the difference in pitch distribution usually have no marked effect upon propeller performances in open water. But, as the effect of pitch distribution will be somewhat clearer in a non-uniform flow, propeller tests over a wide slip range in a wake flow are also intended. A part of this research program is now completed, and some remarks on its results are mentioned in the last part of the paper.