Autopilot automatically keeps the ship's heading.
It controls a steering gear of the ship to keep it on course.
Autopilot have a follow-up mechanism as a pilot system, and controls the steering gear.
The actuator that moves the steering gear can be a solenoid valve or a torque motor, and other options. The autopilot controls steering gear in different ways according to the type of actuator.
PT900: Applicable for all type of steering gear for general merchant vessels.