What is AIS and how to use it?

19 September 2016

AIS stands for Automatic Identification System. It is a tracking system for ships and small craft and it identifies, locates and exchanges data with nearby vessels, ground stations and satellites by way of VHF radio transmission of digital data.

AIS allows the broadcast and reception of information to and from vessels. Information might include the vessel’s name, MMSI number, type, size, speed, course, destination, navigational data (eg ‘at anchor’ or ‘Not under Command’’), the vessel’s ETA, it’s next port, last port visited, speed over ground, draft and other relevant dimensional information.  This information can, if accurate, greatly assist the officer of the watch when making navigational decisions as part of his duties.

Vessels fitted with AIS can be tracked by other vessels with an AIS transceiver or nearby coastal base stations (such as Vessel Traffic Services - VTS).  In some cases satellite receivers are now able to receive and broadcast AIS data around the World, making vessel tracking more reliable and accurate.

AIS transmits using type A and type B units. Type A is more complex and therefore expensive and is usually restricted to larger ships and commercial vessels. Type B units are more likely to be fitted to yachts and the information transmitted is less detailed and the unit is usually less powerful making its range no more than 5 - 10 miles in most cases.

Whilst AIS can be very useful when employed for collision avoidance, captains and crew are still required to use all means available to avoid collision and as recognised means include sight, radar and sound, light and radio signals, the navigator that does not do so will be severely exposed to criticism in the event that he relies solely and unsuccessfully on AIS for these purposes.

In recent years, smaller personal AIS units have become popular for yacht crew and sea-goers. They Transmit a location locally which can prove invaluable if a crew member falls overboard. The AIS transmitter has the advantage that it broadcasts locally to vessels in the immediate area, exactly those vessels most likely to be able to promptly recover you. Some personal AIS beacons are now small enough to fit snugly inside a lifejacket and can be activated automatically.

You can see our live AIS position on this page.

Photo credit © Fierce Turtle 

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