Stability Considerations for Existing Conventional Autopilots on Modern Ship Types

The directional stability of three modern ship types with conventional nonadaptive autopilots is examined. It is shown that while attempting to improve the course-keeping ability of these ships, the potential exists for the operator to unknowingly cause a loss of directional stability with the controls available to him. Stable controller settings are established to prevent such an occurrence. The results of a design method allowing optimization of the autopilot to achieve a desired degree of stability controllability versus steering-induced added resistance is also presented.