ABSTRACT
An evaluation of a recently developed vulnerability criterion for ship course-keeping instability in following waves is presented. This dynamic instability can appear in moderate Froude numbers and it is of parametric type, meaning that it is manifested as an oscillatory growth of yaw amplitude. The criterion was developed from a relatively simple analytical estimation of the instability region’s boundary, by applying the harmonic balance technique on a suitable third-order yaw equation, accounting for the sway-yaw-rudder motions. In the current paper, the surge motion was incorporated in the model and its effect on the boundary of the instability region, and thus on the accuracy of the developed criterion, was examined. Course stability charts depending on the wave characteristics and the ship’s rudder control gains were produced. Moreover, the evaluation was extended for various desired headings of the ship in a stern/quartering wave context.
