AIS (Automatic Identification System) uses a boat’s VHF radio and GPS system to send information about that boat’s position, course and speed to over vessels also equipped with an AIS device and shore-based stations. This can then be plotted on an electronic chart plotter, computer display or compatible radar. This information can help in situational awareness and provide a means to assist in collision avoidance.  In addition, AIS can be used as an aid to navigation, by providing location and additional information on buoys and lights.

There are two classes of AIS, Class A and Class B, as well as different types of AIS used for shore stations (AIS Base Stations), aids to navigation (AIS AtoN), AIS on search and rescue aircraft and AIS search and rescue transmitters (AIS SART).

Class A has been mandated by the International Maritime Organization (IMO) for vessels of 300 gross tonnage and upwards engaged on international voyages, cargo ships of 500 gross tonnage and upwards not engaged on international voyages, as well as passenger ships (more than 12 passengers), irrespective of size.

Class B provides limited functionality and is intended for non-SOLAS vessels. It is not mandated by the International Maritime Organization (IMO) and has been developed for vessels such as work craft and pleasure craft.

An AIS unit uses VHF radio frequencies to transmit its position via a VHF aerial (which can be the same aerial as the VHF fixed radio uses, so long as a VHF splitter is used, but can also be a separate aerial).  In return a transceiver will receive the positions of any vessels with an AIS unit fitted.  Some versions contain a screen so information about any nearby vessel transmitting AIS data shows up on the screen and can be read by the crew or they connect to the GPS chart plotter to provide a visual aid.  An AIS signal provides data about a vessel’s position, speed and course helping to reduce the risk of collission.  Because the AIS works by using VHF frequency it’s range is limited to line of sight and is restricted by the height of the aerial on the boat and the height of the other vessel or AIS Base station.

If you have a second hand boat then it’s worth checking the AIS unit quite early on in your preparations especially if you are changing the name of the boat.  Several crews in the 2014 Great Pacific Race had problems when the AIS unit that came with their boat had to be sent back to the manufacturers before it could have details (such as the boat name the unit transmitted) changed.  Some crews also had problems when their AIS unit was receiving but not sending AIS data making them virtually invisible to other  vessels.


Click here to download a report by Practical Boat Owner of a test they conducted on 18 AIS units.

[download id=”1074″]

Click here to take a look and see what is happening in the area around Monterey Bay right now!

In the USA, AIS units are programmed by the manufacturer. That means that if you by a second hand boat and need to change details of ownership including new registry information that you will need to send your AIS unit back to the manufacturers for this to be done. (this is also the case of DSC VHF radios)

However, we do have access to some AIS reprogramming software which we have included below for two of the most popular AIS units. We can’t guarantee that this will work but it may be worth giving this a try.