Ship–structure collisions pose a significant threat to coastal and offshore infrastructures such as bridge piers, breakwaters, and protective dolphins. In this study, we investigate the performance of a rotational fender system (RFS) that dissipates ship-collision energy through the rolling-induced conversion of translational kinetic energy into rotational kinetic energy. Numerical simulations were conducted using LS-DYNA for ship-collision velocities of 5, 7, and 10 kn and collision angles of 0–75°, with the angles configured to reflect the realistic approach directions of a drifting ship after losing maneuvering control. Within these simulations, the collision response was quantified using a numerical sensing approach. The RFS reduced the peak impact force by 71.47–92.60%, with an average reduction of 83.15%, and delayed the occurrence of the peak force by 0.190–0.464 s. Although the absolute impact force increased with velocity, the reduction efficiency remained consistent, confirming the robustness of the system. These results demonstrate that the RFS effectively transforms impulsive collision loads into gradual and time-distributed responses, alleviating dynamic amplification and local stress concentration. The RFS thus provides a lightweight, modular, and retrofittable protection technology suitable for both new and existing marine infrastructures, which enhances the structural safety and cost-effectiveness of marine infrastructures under realistic drift-collision scenarios.