Autopilot interaction (maneuvering)

Autopilot interaction in maneuvering is the coupling between a course-keeping controller and the hull’s yaw dynamics, where the rudder commanded by the autopilot feeds back into the sway-yaw equations and reshapes the response. A proportional-derivative heading law of the form rudder = k1(psi - psi_desired) + k2 r adds to the ship’s own Nomoto or Norrbin dynamics, so autopilot gains alter overshoot, settling, and the effective course stability seen in a zigzag. Over-tight gains cause rudder-induced oscillation and added resistance from constant helm; loose gains let heading wander. It matters for fuel use and for interpreting trial data where steering is not pure manual helm.