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What is AIS?
The marine Automatic Identification System (AIS) is a location and vessel information reporting system. It allows vessels equipped with AIS to automatically and dynamically share and regularly update their position, speed, course and other information such as vessel identity with similarly equipped craft. Position is derived from a GPS system and communication between vessels is by VHF digital transmissions (on channels specifically allocated within the normal marine VHF spectrum). A sophisticated and automatic method of time sharing the radio channel is used to ensure that even where a large number of vessels are in one location, blocking of individual transmissions is minimised with any degradation of the expected position reporting interval indicated to the user. Even if the unit suffers extreme channel overload conditions it will always recover to normal operation.
There are two classes of AIS unit fitted to vessels - Class A and Class B. In addition, AIS base stations may be employed by the Coastguard, port authorities and other authorised bodies. AIS units acting as aids to navigation (A to Ns) can also be fitted to fixed and floating navigation markers such as channel markers and buoys. Class A units are a mandatory fit under the safety of life at sea (SOLAS) convention to vessels above 300 gross tons or which carry more than 11 passengers in International waters. Many other commercial vessels and some leisure craft also fit Class A units. Class B units are currently not a mandatory fit but authorities in several parts of the world are considering this. Class B units are designed for fitting in vessels which do not fall into the mandatory Class A fit category. The Digital Yacht SMARTERTrack AIT250 is a Class B unit.
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Connect to a plotter or PC to view AIS targets...
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Hook up the AIT250 to an on board PC or plotter compatible with AIS data and you’ll get a detailed overlay of all targets within range onto the display. See the vessels position, course, speed, heading, previous track, length, beam and identity (MMSI, callsign and name).
Class A systems may also show IMO number (if known), navigational status, rate of turn, draught, cargo type, destination and safety related messages. Many systems can then calculate CPA (closest point of approach) and TCPA (time to CPA) for a selected target. AIS systems offer ranges of up to 20-50 miles - typically similar to the maximum ranges expected from normal VHF voice communications. AIS systems complement radar and plotter systems with positive target identification and greatly improve ship safety and security with reduced risk of collision.
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