We present a new method determining a form factor from resistance test results. The total resistance coefficient is approximated by a straight line and a polynomial expression in the present method. The straight line and the polynomial expression represent a viscous resistance and a wave-making resistance, respectively. It is shown that existing flat plate friction formulae are expressed as straight lines, and its inclination is only a function of the form factor. We determine the inclination (form factor) and coefficients of the polynomial expression by means of a linear least-squares method. The features of the present method are that: the form factor is decided without extrapolation; all measured data of resistance testing can be used in this analysis, although low-speed range data should be selected in the Prohaska's method. Using the ITTC57 correlation line, the values of the form factors obtained by the present method are almost the same as by Prohaska's method. It is found that the influence of the unreliable extra low-speed range data in the present method is less than in the Prohaska's method.
