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

Presenter: Olivia Roach, Aerospace and Ocean Engineering

Authors: C. Judge, O. Roach, A. Ibrahim, J. Gilbert, C. Gilbert

Abstract: High-speed planing craft are popular vessels but are prone to dynamic instabilities like chine walking and porpoising. Little is known about porpoising of stepped hulls, and about chine walking for any hull forms. Experiments to induce both instabilities in a lab setting were carried out at the US Naval Academy on a double stepped planing hull. The model was run at two different displacements, and the position of the longitudinal center of mass was varied. Experiments were conducted with a free-to-heave, -pitch, -roll set up and either free-to-yaw or fixed in yaw. Porpoising is more likely for the lighter displacement hull, but chine walking is equally likely for both displacements. It was observed that porpoising 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. As the vessel speed 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 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.