IMO Performance Standards for Auto Pilots (Heading Control Systems)

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  • Within limits related to the ships’s manoeuvrability 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.
  • A heading control system may work together with a track control system adjusting its heading for
    drift.
  • A tum rate control for performing turns may be provided.

Functional Requirements

Adaption to steering characteristics and environmental conditions

The heading control system should be capable of adapting manually or automatically to different steering characteristics of the ship under various speed, weather and loading conditions, and provide reliable operation under prevailing environment and normal operational conditions.

Performing Turns

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 tum.

Rudder Angle Limitation

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. When other means of directional control are used the requirements of this section should appropriately apply.

Permitted Yaw

Means should be incorporated to prevent unnecessary activation of the rudder due to normal yaw motion.

Preset Heading

Any alteration of the preset heading should not be possible without intended action of the ship’s personnel.

Limiting of Overshoot

The heading control system should change to a preset heading without significant overshoot.

Change over from Automatic to Manual Steering and vice-versa

  • Change-over from automatic to manual steering and vice-versa should be possible at any position
    of the rudder and should be effected 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.
  • 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.
  • Adequate indication should be provided to show which method of steering is in operation.

Change-over from Track Control to Heading Cpontrol

  • 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.

Alarms and Signalling Facilities

Failure or reduction in power

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.

Off-heading Alarm

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.

Heading Monitor

  • If the ship is required to carry two independent compasses, a heading monitor should be provided to monitor the actual heading information by independent heading sources. The heading monitor is not required to be an integrated part of the heading control system.
  • An alarm both audible with mute function and visual should be provided when the heading information in use deviates from the second heading source beyond a preset limit.

Indication of Heading Source

A clear indication of the actual heading source should be provided.

Sensor Status

  • The heading control system should provide an indication when any input from external sensors used for control is absent.
  • The heading control system should also repeat any alarm on the status messages concerning the quality of the input data from its external sensors when they are used for control.

Controls

  • 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.
  • 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 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.
  • 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.
  • Except for the preset heading setting control, the actuation of any other control should not significantly affect the heading of the ship.
  • Additional controls at remote positions should comply with the provisions of this performance
    standard.

Interfacing

  • The heading control system should be connected to a suitable source of heading information.
  • 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.
  • 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.”