Abstract: Objectives In the preliminary design phase, predicting and assessing the aerodynamic performance and propulsion effect of rotor sails are essential for rational selection and optimal design of these rotors for ship applications. Methods Thus, the aerodynamic performance of the rotor sail was first subjected to unsteady-state calculations based on computational fluid dynamics (CFD) methods in this study, and the results were verified against experimental data. Secondly, the influence of the base on the aerodynamic performance of the rotor sail was investigated, and the aerodynamic performance of the rotating cylinder under different length-to-diameter ratios and endplate diameter ratios was calculated and compared. Finally, based on the available power calculation method for rotor sail specified in MEPC.1/Circ.896, the available power of different types of rotor sail was calculated and compared. Results The results show that the presence of the base affects the flow field distribution at the bottom of the rotor sail, reducing the extent of the low-pressure region on the spinnaker sail surface and leading to a reduction in the lift coefficient. When the height of the rotor sail is fixed, there exists an optimal length-to-diameter ratio, i.e., an optimal diameter, which maximizes the available power of the rotor sail. Conclusions The findings of this study can serve as a reference for the matching design and selection of shipboard rotor sail and for the evaluation of propulsion effects.