Abstract: A real-time ship steering system provides steering of a survey ship along a rescribed thumb line track in accordance with a received point location on the thumb line and a received heading of the rhumb line. The system of the present invention requires an integrated navigation system, a track-keeping interface, and a ship autopilot to steer a ship. The computer of the navigation system integrates position data from continuous fixed radio and satellite positioning systems, inertial navigation systems, and dead reckon aids to develop the best present position. At prescribed equally spaced times, the best present position is used to compute the off-track distance of the ship. The off-track distance is used to develop proportional and integral heading corrections, which are applied to the autopilot by way of the track-keeping interface. The autopilot accepts the correction signal as a bias to the desired ground track heading, causing the ship to be steered toward the desired track.