Dynamic instability of a high-speed planing boat model

A series of bare-hull resistance and self-propulsion tests were carried out on a 1/8 scale model of a 11.8 m long, waterjet-propelled planing hull in the clear water towing tank at the National Research Council of Canada's Institute for Marine Dynamics. The bare-hull resistance tests, performed with the waterjet inlets closed, spanned a range of eight model velocities and nine ballast conditions consisting of three displacements each with three positions of the longitudinal center of gravity. The hull was then fitted with two model waterjet thrusters and tested over the same speeds and ballast conditions. Dynamic instability, or porpoising, was seen during certain high-speed tests. A discussion of this behavior and its relation to published dynamic stability limits is given.