抄録
The number of installing Highly Skewed Propellers (HSP) behind merchant ships have been increasing considerably for the purpose of reducing propeller induced pressure fluctuations. Many results of experiments about the effect of HSP have been reported and the usefulness of HSP to reduce pressure fluctuations has been confirmed. Although the amount of effects seems to be much varied among experiments. The purpose of present report is to find the simple and accurate relations between the skew angle and the amount of reducing propeller induced pressure fluctuations. Two kinds of data were used to find the relations. One is the experiments carried out by authors and the other is the results reported in references. Authors used four model propellers having skew angle 0, 20, 40 and 60 degrees designed to have nearly same spanwise load distributions. Pressure fluctuations on a flat plate above the propellers were measured for four sets of tip clearace and three kinds of simulated wake fields in the cavitation tunnel. The experimental results indicated that tip clearance Z_t/D below 0.25 and the wake distribution have scarcely no effect on the reducing ratio of pressure fluctuations due to skews. Then further attention was payed for the relation between the pitch distribution and the skew angle. After Johnsson the amount of decreasing pitch near the propeller tip required to have same spanwise load distribution for increased skew angle was obtained. Using the above relation, data corresponding to the operating conditions of usual merchant ships, 0.18<K_T<0.22, 1.8<σ_n<3.6 and 0.05<Z_t/D<0.27 were analized. As a result the fairly good relations between the skew angle and the reducing pressure fluctuations under the same spanwise load conditions and the same pitch distributions were obtained
