Abstract: A small waterplane area twin-hull (SWATH) ship with inclined struts and the DARPA (Defense Advanced Research Projects Agency) Suboff model as torpedoes and an NACA (National Advisory Committee for Aeronautics) airfoil as the strut cross section is developed. Based on this design, a systematic and targeted study based on CFD has been conducted to figure out how the torpedo submergence depth impacts the resistance of the torpedo and the entire ship of the SWATHmodel above. Viscidity was consi-dered. It is found that, through the study, the torpedo submergence depth has a significant impact on the hull resistance of a SWATH with inclined struts， and the impact increases with speed rising. Although the wave makes resistance of torpedoes near the free surface increase obviously with the torpedo submergence depth decreasing, the total resistance of the whole ship decrease obviously with the torpedo submergence depth decreasing.

Key words: small waterplane area twin-hull (SWATH) with inclined struts, submergence depth, resis-tance, viscosity, torpedo hull