Autopilot is basically used when ship has to steer a set course for a long time without alteration because any deviation from the set course is controlled electronically and automatically.
This will not only relieve the helmsman from steering duties but is also more efficient because as soon as the ship deviates from the set course, corrective action is taken immediately using requisite amount of helm to bring the ship back to the set course
The marine autopilot receives signals from directional sensors such as the gyrocompass and uses them to automatically control the helm for navigation.
As per SOLAS Chapter V, regulation 19.2.8, all ships of 10,000 gross tonnage and upwards shall have a heading or track control system, or other means, to automatically control and keep to a heading and/or straight track.
IMO PERFORMANCE STANDARDS FOR MARINE AUTOPILOTS AND HEADING CONTROL SYSTEMS
Autopilots and heading control systems fitted onboard ships shall meet the following performance standards
- The heading control system should be connected to a suitable source of heading information.
- Within limits related to the ship’s maneuverability the heading control system, in conjunction with its source of heading information, should enable a ship to keep a preset heading with minimum operation of the ship's steering gear.
- The heading control system should be capable of adapting manually or automatically to different steering characteristics of the ship under various speeds, weather and loading conditions, and provide reliable operation under prevailing environment and normal operational conditions.
- Unless features for automatic adjustment are incorporated in the installation, the heading control system should be provided with adequate controls to adjust to effects due to weather and the ship's steering performance.
- The number of operational controls should be such that easy and safe operation can be achieved. The controls should be designed to preclude inadvertent operation.
- Any alteration of the preset heading should not be possible without intended action of the ship's personnel.
- The heading control system should be designed in such a way as to ensure altering the pre-set heading to starboard by turning the heading setting control clockwise or tilting it to the right-hand side. Normal alterations of heading should be possible by one adjustment only of the preset heading control.
- Except for the preset heading setting control, the actuation of any other control should not significantly affect the heading of the ship.
- The heading control system should change to a preset heading without significant overshoot.
- A heading control system may work together with a track control system adjusting its heading for drift.
- If a heading control system is capable of digital serial communication with the ship's navigation system then the interface facilities should comply with the relevant international marine interface standards.
- If the heading control system works as part of a track control system, then when switching from track control to heading control, the actual heading should be taken as the preset heading.
- Any switching back to track control shall not be possible without intended action of the ship's personnel.
- A turn rate control for performing turns may be provided. The heading control system should be connected to a suitable source of speed information when it is used in a turning radius mode or when any control parameters are automatically adapted to speed. The heading control system should be able to perform turns, within the turning capability of the ship, based either on a preset turning radius or a preset rate of turn.
- Means should be incorporated in the equipment to enable rudder angle limitation in the automatic mode. Means should also be available to indicate when the angle of limitation has been commanded or reached.
- Means should be incorporated to prevent unnecessary activation of the rudder due to normal yaw motion.
- Where remote control stations are provided, facilities for the delegation of control to the remote station and unconditional return of control should be incorporated in the master station.
- There should be a single change-over control which should be located in such a position that it is easily accessible to the officer of the watch. Change-over from automatic to manual steering and vice-versa should be possible at any position of the rudder and should be executed by one manual control within 3 seconds.
- Change-over from automatic to manual steering should be possible under any conditions including any failure in the automatic control system.
- When changing over from manual to automatic steering the heading control system shall take over the actual heading as the preset heading.
- Adequate indication should be provided to show which method of steering is in operation.
- An alarm both audible with mute function and visual should be provided in order to indicate failure or a reduction in the power supply to the heading control system or heading monitor, which would affect the safe operation of the equipment.
- An off-heading alarm, both audible with mute function and visual should be provided when the actual heading deviates from the preset heading beyond a preset limit.