Optimized propeller–PBCF spacing for enhanced ship propulsion efficiency

Ship propulsion efficiency plays a crucial role in reducing fuel consumption and greenhouse gas emissions in the maritime industry. While Propeller Boss Cap Fins (PBCFs) are widely adopted to suppress hub vortices and enhance wake flow, the influence of axial spacing between the propeller and PBCF remains underexplored. This study examines the impact of propeller–PBCF spacing on hydrodynamic performance using Computational Fluid Dynamics (CFD) simulations based on the Reynolds-Averaged Navier–Stokes (RANS) approach in ANSYS Fluent 2023. A 600 mm B-series propeller representative of electric boat applications was modeled. Numerical reliability was ensured through grid independence testing and validation against experimental data. Key performance parameters—thrust and torque coefficients, wake fraction, pressure distribution, and turbulence kinetic energy (TKE)—were analyzed. Results indicate that axial spacing significantly affects wake dynamics and propulsive efficiency. The optimal configuration occurred at a axial spacing ratio of 0.2c (31.2 mm), yielding a 2.25% efficiency improvement at an advance coefficient (J) = 0.346 compared with the baseline. Flow visualization revealed reduced wake asymmetry, diminished low-pressure cores, and lower turbulence intensity. These results identify axial spacing as a previously neglected but practical design variable for improving propeller hydrodynamics and advancing energy-efficient ship propulsion.