Power Prediction Based on Modified Yamagata Resistance Chart and Newly Introduced Thrust Deduction and Wake Factors

Abstract

The aim of this paper is to get comparatively reliable speed-horse power curves at primary stage of the basic design of the ship having L between 30^m and 400^m. The author improved the classic method of EHP prediction based on the Yamagata resistance chart, adding residuary resistance coefficients for C_b>0.80 and changing values of B/d_<mld> correction into half. For modern bulbous bow, the author introduced the new correction factor in accordance with C_b. Also for the stern form, the author added the correction factor in relation to the wake fraction. For twin screw ships, the author adopted the correction of the frictional resistance coefficient in stead of adding some percents to the residuary resistance coefficient according to Lap's opinion. With regard to the wetted surface, the author gave modified Todd's formula. As to the thrust deduction factor t and the wake fraction w, the author investigated many model experimental data and gave the new curves of t and w. By using above-mentioned new method, the author believes comparatively reliable calculation results of BHP or SHP for the speed will be expected for the ship of full loaded condition or vicinity.