This paper presents a method of designing hull form o ships except low speed full types to reduce the wave-making resistance at the preliminary design stage. The procedure to be taken is as follows. (1) C_p curve of a main hull without bulb is given as a mathematical formula, ψ_1(ζ)=A cos aζ+B cos 2aζ+C, its coefficients are determined by using the chart which are leaded from the result of calculation based on Thin Ship Theory. (2) C_p curve of a bulbous hull is given by deforming Rankine's Ovoid, in proportion to the wave phase lags corresponding with its main hull. (3) A complex body of both main and bulbous hull to obtain the optimum hull form is drawn numerically and geometrically, with taking consideration of the wave-making non-linear phenomenon.
