Number of people enjoying sailing and cruising is increasing. Acoordingly, number of pleasure boats, especialy illegally moored boats, is increasing. To pre-pare space for mooring of those boats, various marinas or yacht harbors are planned to be constructed. In such planning, full investigation of the harbor tranquility is hardly done and rough waves often cause various troubles in exsiting marinas. Here, the effect of slope of the marina on the harbor tranquility is investigated through numerical and physical model experiment and a procedure for determining the best position of the slope is proposed.