Six-Degree-of-Freedom Motion Analysis of High-Speed Craft Navigating through Variable Marine Environments

The dynamic behavior of high-speed craft navigating through variable sea states plays a pivotal role in ensuring maritime safety. However, many existing simulation approaches rely on linear or overly simplified representations of the marine environment, thereby limiting the fidelity of motion predictions. This study explores the motion characteristics of a 4.5-t high-speed vessel by conducting fully coupled numerical simulations using the STAR-CCM+ software. The analysis considers both calm and varying sea conditions, incorporating fluctuations in wave height, wavelength, and wind speed to reflect more realistic operating scenarios. Simulation results reveal that the vessel’s hydrodynamic response is highly sensitive to changes in sea state. As conditions deteriorate, the free surface becomes increasingly complex, with higher wave amplitudes and more pronounced interactions between the waves generated by the vessel and those imposed by the external environment. These effects lead to significant increases in roll, pitch, heave, and sway motions, thereby imposing greater demands on the vessel’s dynamic stability and operational safety. Furthermore, both hydrodynamic resistance and propulsive thrust exhibit notable dependence on sea state and vessel speed. Total resistance generally increases with rougher sea conditions, while thrust tends to rise with increasing forward speed. Under calm or mildly disturbed waters, a Froude number (Fr) of 0.5 appears to offer an optimal balance for initiating and controlling primary motions such as roll, pitch, heave, and sway. Conversely, in more challenging conditions—such as those represented by a Sea State 3—effective motion control is better achieved at a higher Froude number of approximately 1.0.