AIS

Automatic Identification System

The tracking of ships on this English Channel Ship Movements web site is accomplished using information broadcast from each ship as a part of the Automatic Identification System (AIS) on 2 Marine VHF channels (161.975 MHz - Ch.87 & 162.025 MHz - Ch.88)). Each vessel equipped with the necessary AIS radio transponder, transmits their identification, position, speed and heading, and other information via a data stream on a regular basis. Other ships and shore stations can receive this information and using dedicated display systems, watch the movement of all AIS equipped ships in the area, much like on radar. There are two classes of AIS transmission. Class A must be operational in all shipping over 300 tons. Class B is used by some pleasure craft/diving vessels etc. Class B is not mandatory for these vessels.

The data bursts are received at the Saltdean, East Sussex AIS Receiving Station and plotted using specialised computer programs (see http://www.coaa.co.uk/shipplotter.htm for an overview of the ShipPlotter software used here.) The resulting ship plots are then transferred to this web site for general viewing. Plots are updated every 5 minutes.

Atmospheric conditions can sometimes affect the range at which the AIS signals can be received. At times ships seen on our charts will include those from much greater distances than usual and reception of up to 500 nautical miles can be achieved under exceptional conditions, although normally a range of 50-60 nm can be expected.

Look at the Chart Library for screenshots taken during periods of enhanced propagation.