Chine Walking and Porpoising of A Double-Stepped Planing Hull in Calm Water

High-speed planing craft are very popular vessels but are prone to dynamic instabilities like chine walking and porpoising. While porpoising has been studied experimentally and numerically in the literature, there is little published about porpoising of stepped hulls. There is also very little published about chine walking for any hull forms. Recently, experiments to induce porpoising and chine walking in the laboratory environment were carried out at the US Naval Academy on a double stepped planing hull. The model was run at two different displacements with speeds ranging from 4.2 to 9.7 m/s, and the position of the longitudinal center of mass (LCG) was varied. Experiments were conducted with a free-to-heave, free-to-pitch, and free-to-roll set up as well as either free-to-yaw or fixed in yaw. Kinematic motions and videos of the runs were taken. In these experiments, both porpoising and chine walking were observed. Porpoising is more likely for the lighter displacement hull, but chine walking appears to be equally likely for both displacements. It was observed that the porpoising behavior is a coupled pitch and heave behavior, which confirms previous work for non-stepped hulls. Chine walking was observed to be a roll and yaw coupled behavior, despite Blount and Codega (1992) stating it is only a roll instability. Chine walking appears to be initiated by a roll motion that leads into the yaw motion. As the speed of the vessel increases, the amplitude of the chine walking motion decreases. It was observed that some instances of chine walking also included small amplitudes of motion that indicate porpoising behavior that is not visible in the video but present in the time-history data. The behavior of chinewalking and porpoising together was most notable for the heavier displacement and furthest aft LCG.