[ggchappell]

Very nice, but I had to wonder why, of the thousands of ships whose positions are recorded, only 2 appear to be any significant distance from land. The answer is in the FAQ [1]:

> The MarineTraffic system does not cover all the seas of the world, but only specific coastal areas where a land-based AIS receiver is installed.

[1] http://www.marinetraffic.com/ais/faq.aspx?level1=160#16

[bcl]

The AIS transmissions are VHF (162MHz) so they are fairly short range, although with high gain antennas you can extend it a bit (with a corner reflector I once had intermittent data from a ship 600nm away).

[pixie_]

There's a commercial service that offers global coverage with AIS receivers attached to satellites. http://www.orbcomm.com/services-ais.htm