0n the Effects of Stern-Profile on the Course Stability of Full-Bodied Ships

Abstract

A statistical study on the correlation between course stability and stern-profile of full form ships, both in full and model scale, led us to the following formula. D=k_1 H_PS+k_2H_RS-k_3 (C_B B/d) where D: 1/K'_O K_0': slope of r'∼δ curve at the origin (this is a course stability index) k_l, k_2, k_3: coefficients to be determined by the statistical analysis H_PS, H_RS: stern-profile parameters; cf. Fig. 5 Although the formula consists of only three terms H_PS, H_RS and C_BB/d, the calculated, D values for a number of forms showed a good agreement with the observed ones as is seen in Table 1 and 2. This fact implies that the stern-profiles have an important concern to the course stability; the shallower stern over-hang, the deeper propeller immersion, the wider clearance between stern over-hang and rudder top result apparently in the better stability. This formula will be usefull in ship design for fixing the stern profile and rudder arrangement. This paper also relates to a stern flow survey concerning the effect of stern profile to the course-stability, with a hypothetic interpretation of the result.