Trimaran Small Waterplane Area Centre Hull (TriSWACH) is a concept hybrid hull form between SWATH ships (centre hull) and Trimarans (side hulls). The resistance and seakeeping characteristics of this hullform are currently investigated by the Atlantic Centre for Innovative Design and Control of Small Ships (ACCeSS) consortium, supported by the U.S. Office of Naval Research. The main design advantages of this novel hull are (1) small wave resistance at high speeds; (2) large usable deck area; and (3) superior seakeeping characteristics, compared to monohull ships. Roll damping and response, as key design features for the safety and operational efficiency of the vessel, are currently under investigation. The ultimate goal is to propose an improved method for prediction of roll motions and also investigate how it affects the heaving response of the TriSWACH. This paper presents the findings from roll and heave decay tests, conducted at the U.S. Naval Academy (Annapolis, MD), focusing on the roll damping and the effect of side hull geometry on roll and heave motion coupling. Roll and heave decay tests were conducted for two scale models with different side hull shapes (conventional with haunches and prismatic with no haunches). Significant coupling between roll and heave was observed for the model with conventional side hulls. A quasi-linear method is used to obtain the roll damping coefficients using the experimental data and ITTC recommended semi-empirical method was used to approximate the roll damping coefficients. Both methods have shown good correlation with experimental data.

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