Abstract: Objectives This study aims to investigate the influence and mechanism of cup structure on the hydrodynamic performance of surface piercing propellers.Methods Based on RANS method and combined with VOF method and sliding mesh method, a numerical simulation is carried out on the 841-B surface piercing propellertogether with its cup structure modified propellers under natural ventilation conditions. On the basis of verifying the effectiveness of the numerical simulation method, the trailing edge angle is adjusted based on the dichotomy method to change cup structure of the benchmark surface piercing propeller, and a series of propellers were obtained for simulation calculation and research.Results The research shows that the change of cup structure has a