Numerical Analysis of Motion Stability of a Small Catamaran Under Ship Waves in Shallow Waters

This study investigates the motion stability of a small unpowered catamaran subjected to ship waves in shallow waters. Ship waves generated by large vessels operating in coastal and confined waterways may pose safety risks to nearby small craft. Wave parameters derived from the free-surface results of 2000-ton and 6000-ton vessels simulated in STAR-CCM+ were used as inputs for time-domain motion analysis in ANSYS AQWA. The results show that pitch motion is the dominant factor affecting stability, particularly under head-wave conditions, while roll motion remains within safe limits. The analysis provides case-specific conservative speed guidance of 14–16 kn for the 2000-ton vessel and 17–21 kn for the 6000-ton vessel when the small vessel is located 1–3 ship lengths away from the passing large vessel. These findings provide a numerical reference for speed management of large vessels operating near small craft in shallow and restricted waterways.