What is Autopilot, its principle and details?

Written by Amit Sharma

An autopilot (or pilot) is a mechanical, electrical or hydraulic system which can maintain a vessel on a predetermined (set) course without the need for human intervention. Using a direct or indirect connection with a vessel’s steering mechanism, the autopilot relieves the crew from the task of manually steering the ship.

Autopilot have evolved from simple course holding systems to adaptive computer systems that offer reduced fuel costs and increased transit times. These new systems learn the characteristics of the vessel’s handling and minimize rudder movement reducing drag on the vessel. Increased speed and lower fuel consumption makes autopilot more user friendly.

Autopilots do not replace a human operator, but assist them in controlling the ship, allowing them to focus on broader aspects of operation, such as monitoring the trajectory, weather and systems.

  • This instrument is not to replace the helmsman.
  • It is not to be used in restricted waters or during manoeuvring.
  • Not to be used for large alterations of more than 15-20
  • Autopilot will operate efficiently over a certain speed (approx. > 5 knots), below which it will start to wander.
  • Autopilot is normally used when ship has to steer same course for long period of time.


What is working principle of autopilot system?

An output from a gyro or magnetic repeating compass is coupled to a differential amplifier along with a signal derived from a manual course-setting control. If no difference exists between the two signals, no output will be produced by the amplifier and no movement of the rudder occurs. When a difference is detected between the two sources of data, an output error signal, proportional in magnitude to the size of the difference, is applied to the heading error amplifier. Output of this amplifier is coupled to the rudder actuator circuit, which causes the rudder to move in the direction determined by the sign of the output voltage. The error signal between compass and selected course inputs produces an output voltage from the differential amplifier that is proportional to the off-course error. This type of control, therefore, is termed ‘proportional’ control. As it  has been shown, the use of proportional control only, causes the vessel to oscillate either side of its intended course due to inertia producing overshooting.

About the author

Amit Sharma

Graduated from M.E.R.I. Mumbai (Mumbai University), After a brief sailing founded this website with the idea to bring the maritime education online which must be free and available for all at all times and to find basic solutions that are of extreme importance to a seafarer by our innovative ideas.