Experimental investigation of the effects of transverse step position and height on the hydrodynamic performance of an asymmetric catamaran craft in calm water

High-speed catamarans are widely recognized among planing hull configurations due to their superior hydrodynamic stability. The incorporation of transverse steps can enhance performance by promoting flow separation, reducing wetted surface area, and consequently lowering resistance while improving dynamic stability. This study experimentally investigates hydrodynamic performance of an asymmetric twin-hull craft derived from a modified 2.5m Fridsma mono-hull series with deadrise angle of 30° and length-to-beam ratio of 5. Baseline experiments were first conducted on the bare hull at speeds of 1–8 m/s, corresponding to longitudinal Froude numbers (Fn) of 0.2–1.6. To improve performance, transverse steps were introduced at three longitudinal positions (Ls = 650, 750, and 850 mm) and three step heights (Hs = 15, 20, and 25 mm). All stepped configurations were tested over same speed range. Throughout the experiments, displacement was maintained at 48 kg and longitudinal center of gravity was fixed at 34% of the craft length from the transom. Results showed that transverse steps significantly influence resistance, trim, and rise-up characteristics. Optimum configuration was Ls3-Hs3, achieving a maximum trim reduction of 12.4% and a resistance reduction of 74.5% at Fn = 1. Furthermore, stepped configurations exhibited improved dynamic stability, remaining balanced and stable for Fn > 1.