Mitigating Roll Response of High-Speed Catamarans by dual demihull mounted T-Foils, Part 2: Closed-Loop Tests in Regular Waves

Building on open-loop calm water investigations presented in Part 1, this study advances to closed-loop towing tank experiments to evaluate the effectiveness of a new RCS configuration, featuring dual demihull-mounted T-Foils and transom-mounted stern tabs, in reducing roll response. A roll control algorithm was developed to actively deflect the T-Foils and stern tabs based on real-time roll response feedback. Experiments were conducted at a model speed of 2.89 m/s (37 knots full scale) in Regular Waves with height of 60 mm and 90 mm (2.7 m and 4 m full scale), using a 2.5 m catamaran model towed at a 2° drift angle with bow to port to induce roll motion in encountered waves. The RCS was tested in three conditions: No RCS, passive RCS, and active RCS with linear and nonlinear roll control algorithms. The nonlinear roll control algorithm was most effective, reducing peak roll response by 58% in moderate waves and 43% in large waves. Overall, the new RCS mitigated roll, pitch, and heave motions in moderate waves by 58%, 34%, and 25%, respectively, demonstrating the potential of demihull-mounted T-Foils to enhance roll control while maintaining heave and pitch motion control effectiveness. Local vertical motion analysis showed the highest motion response at the bow-starboard and the lowest at the midship-port location, highlighting the influence of wave impact, drift-induced asymmetry, and combined motions. The results of this study offer valuable guidance for future RCS design in high-speed vessels.