Recently, many research works have been contributing toward ship hull forms being represented by more exact singularities distribution. Most of them were based on the assumption of the thin ship in which singularities are distributed on ship's center plane. The authors examined the limitation of the thin ship approximation by numerical works. It proved that this approximation was appropriate only to extremely thin ships. One numerical method for calculating singularity distribution on the ship surface was developed considering the wave making effect. In this method the ship surface was replaced by many squared patches. For two mathematical hull forms, the singularity distributions were determined by this calculus, and the calculated wave making resistances were compared with the experimental results.