One of the main optimization problems for the performance and comfort of yachts is the wet swimming platform problem, also known as the rooster-tail phenomena .And this research presents an investigation using Computational Fluid Dynamics (CFD) method for a real case of an 88 ft. semi-planning motor yacht hull form that encountered this phenomena. First of all, the original hull form was analyzed to define the problem at cruising and maximum speeds, 14 knots, and 24 knots respectively. To solve this problem, modifications to the stern form of the hull were made in a two-step iteration. Initially, the size of the current interceptor was increased with a tunnel wedge. Results of the CFD analysis show that this modification eliminated the wet platform problem and increased the top speed of the yacht. Since the applicability of the wedge to mount is complex and costly, a second analysis with only enlarged interceptors was performed. As a result, the wet platform problem is solved, however, the resistance reduction was slightly lower.