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To investigate the vibration and noise reduction effects of Propeller Boss Cap Fins (PBCF), the Large Eddy Simulation (LES) method has been employed in the noise performance estimation of a propeller-rudder system. The hydrodynamic performance of the propulsion system is predicted after the grid independence analysis, then further compared with the result of cavitation tunnel experiment. The acoustic simulation is performed based on Ffowcs Williams and Hawkings (FW-H) equation. After the observation of the hydrodynamic noise performance changes, the forces of propulsion systems and noise reduction effects of PBCF are analyzed. It’s indicated from the research results that PBCF can not only improve the propulsion efficiency, but also reduce the radiation noise intensity significantly. Meanwhile, the lateral force fluctuation of hub cap can be decreased by suppressing the vibration of propeller shaft. In addition, the time-averaged value of the rudder lateral force has been decreased by about 15.5%. It has been well known that the radiation of propulsion noise is directional. Accordingly, it is found that the noise reduction effects due to PBCF are also directional, which is the most noticeable in the axial direction.