The Automatic Identification System (AIS) is a system for the automated exchange of messages between ships by VHF radio which allows ships and traffic monitoring systems (CROSS in France) to know the identity, status, position and the ship route in the navigation zone.
Chapter V of the SOLAS Convention required that ships of over 300 gross tonnage engaged on international voyages be equipped with this device by July 2007 at the latest.
For commercial vessels, the system must be interfaced to an external computer for possible use by a pilot.
Every 2 to 10 seconds, a ship equipped with AIS transmits the following information (NB: some additional sensors are needed for this list):
- MMSI number : unique identifier of the vessel
- Navigation statutes, for example: moored, anchored, en route to engine, limited maneuverability, beached, fishing operations, handicapped by draft, sailing (this information is not Always very reliable because indicated by the shift supervisor who sometimes forgets to change status, we can name many examples of ships "moored" in the middle of the ocean sailing at 15 knots)
- The road on the bottom followed by the ship
- The speed on the bottom followed by the ship
- Speed of course change (instantaneous rate of turn)
- Position: latitude and longitude with an accuracy of 1/10000 of a minute (unreliable accuracy today)
- True Cape (information from a compass)
- UTC time
In addition, every six minutes the following information is transmitted:
1- Selective call number
2- Ship name
3- Type of vessel or cargo (eg dangerous goods)
4- Dimensions of the ship
5- Position of the AIS antenna on the ship
6- Type of satellite positioning instrument: GPS or DGPS
7- Draft (updates at the initiative of the shift supervisor)
8- Destination (updates at the initiative of the shift supervisor)
9- ETA : Estimated Time of Arrival at destination (updates at the initiative of the shift supervisor)
10- Number of people on board the ship (updates at the initiative of the shift supervisor)
It is possible to cut the transmission of data, this possibility must be made knowingly, because it will be possible in the event of a sea event (for example: boarding, SAR operations) to know the time later. The cutting of these programs remains under the full responsibility of the captain. Turning the control panel (DCU) off does not stop the transmission of data, you must enter a menu. Stopping the DCU can disrupt the integrated navigation system if it is part of it.
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As for on-board professional applications, the superposition of AIS data on a radar image for example, greatly improves the reading of traffic from the bridge, particularly in bad weather. The same goes for bypassing storms or hurricanes during transoceanic voyages subject to these frequent events: the superposition of AIS data on the weather image makes it possible to stay offshore and adapt in real time.
Another application that interests both professionals and boaters is the insertion of an AIS beacon in a life jacket. This greatly facilitates rescue operations, especially when the elements are raging and the man overboard is regularly masked by the movement of the waves.
