Introduction  The ship resistance directly affects the fast performance of the ship, for an offshore wind farm service vessel, the fast performance is one of the important performance indexes. Therefore, it is necessary to calculate the ship resistance and study the effective resistance optimization method.

  Method  Based on the CFD method, a numerical model was established to study the resistance performance of a 19.1 m-long catamaran offshore wind farm service vessel, the resistance of the ship at four different speeds of 10 kn, 13 kn, 16 kn and 20 kn were calculated and analyzed, and a stern flap was installed at the stern of the ship as the optimization method. Three stern flap schemes with different installation angles were designed. The ships before and after optimization were numerically simulated, and the calculation results were compared and analyzed.

  Result  The research shows that the installation of stern flap with appropriate installation angle at the stern of the ship can effectively improve the resistance performance of the ship during navigation. The resistance reduction effect is ideal. The optimization method can change the navigation attitude of the ship and reduce the heave and trim angle of the ship during navigation.

  Conclusion  The research results can provide reference for the calculation of ship resistance performance and the design of optimization method.