The positions of the vast majority of the vessels displayed on MarineTraffic are based on the collection of AIS (Automatic Identification System) signals which are transmitted by onboard AIS transponders installed on these vessels.

All vessels over 299GT (Gross Tonnage) are required to carry an AIS transponder on board which (among some other static information, such as the vessel’s name, dimensions and voyage details) transmits their position, speed and course. Smaller vessels may optionally use the lower cost "Class B" AIS Transponders to transmit AIS signals.

All AIS transponders periodically transmit the above-mentioned information using dedicated VHF radio frequencies and make it available to the public domain. Our network of AIS-Receiving Stations collects this information and publishes it on our web-site.

The limitation of this method is that the vessel must be within the range of one of our coastal AIS receivers (i.e. within a distance smaller than 30 NM from a receiving station, on average) in order for the AIS-receiving station to be able to pick-up her signal.

Under this perspective, if your boat is equipped with an AIS-transponder all you have to do is to make sure that it is working properly!