The purpose of this study is to propose a procedure for accurate calculations of the flow field around prismatic stepped planing surfaces by using an existing commercial CFD code (STAR-CCM+), and investigate the characteristics of hydrodynamic phenomena including their scale effects. In the previous studies3), it is shown that high resolution of partial mesh around stagnation line and application of surface tension model are significant to obtain highly accurate calculation results. The same procedure is also applied for prismatic stepped planing surfaces with one step or two steps, and the hydrodynamic forces acting on prismatic stepped planing surfaces are calculated and the calculated results are compared with measured results. The characteristics of the flow field on the hull behind step are investigated, and the frictional resistance coefficient is obtained for each hull. The calculated coefficients for Reynolds number using average length of each wetted surface as representative length are near the turbulent frictional coefficient line of the equivalent flat plate. In addition, the 10 times large prismatic stepped planing surface with one step is calculated to investigate the scale effects on the wetted surface and its frictional resistance coefficient. As the result, the wetted surface area behind step has the scale effects that is nondimensional value of large hull is smaller than model hull caused by the difference of frictional force which comes from Rn differences on the wetted surface in front of the step.
