The ShipPlotter Software displays complete information about ships that are within VHF range of your position. ShipPlotter is using the Universal Automatic Identification System (AIS).
AIS is a system that ships use to communicate their positions to each other as part of the global maritime safety system. From December 2004, all ships over 300 tons must carry an AIS system which broadcasts information about the ship to any suitably equipped receiver.
Ships broadcast their identity, position, course, speed and destination so that other ships can take account of their movements. By using a low cost radio scanner tuned to one of the AIS channels, the ShipPlotter software, that is running on your PC, will be able to display a radar-like real-time map of all the large ships manoeuvring in your area together with information about their destination, estimated time of arrival and even the dimensions of each vessel.