Comparison of 3-DOF and 6-DOF CFD Maneuvering Simulations for a Fully Wind-Powered Ship

This study investigates the effects of roll, pitch, and heave on the motion characteristics of a fully wind-powered ship equipped with two rigid wing sails. While previous research by the authors demonstrated that L-shaped and T-shaped sail arrangements improve thrust generation and maneuverability, the importance of six-degree-of-freedom (6-DOF) motion modeling has not been fully clarified. To clarify this open question, the present work provides a systematic comparison between the 6-DOF model and a simplified three-degree-of-freedom (3-DOF) model in which roll, pitch, and heave are constrained. Four sail configurations are analyzed under true wind directions of 150° and 180°. The comparison reveals that the 3-DOF model cannot accurately reproduce key features of the ship’s trajectory, drift angle, and speed, particularly for cases where aerodynamic–hydrodynamic coupling strongly affects yaw stability. In contrast, the 6-DOF simulations reveal substantially different steady-state behavior and demonstrate that roll, pitch, and heave play an essential role in predicting maneuvering performance. The results clarify how sail arrangement and motion modeling interact to shape the maneuvering characteristics of fully wind-powered vessels, providing fundamental insights for the development of reliable 6-DOF simulation frameworks and for the design assessment of next-generation wind-propelled ships.