The incompressible Reynolds Averaged Navier-Stokes (RANS) code using the multiblock grid method has been developed for simulating the steady free surface flows over ship having complex geometries. “Horizontal Mode”, “Vertical Mode” and “BJ-SGS” which are methods of updating boundary conditions on block interfaces are incorporated in the present code and investigated in the computation of free surface flows about Wigley hull. The new code is applied to computation of transom stern flow about a container ship and a high speed vessel and those numerical results are compared with the experimental results.