Live Ships Map - Vessel Traffic and Positions
marinetraffic.com
marinetraffic.com
It also broadcasts the ship name, registration number, physical size, tonnage, loading and other information.
Interestingly, although it's required by law that it be carried, it is not required by law that it be turned on.
Note, the above is all from memory, and some may be a little out-of-date or inaccurate. It's close enough to give you the idea, and if you want more accuracy it's easy to look up.
From "The December 2002 amendments" http://www.imo.org/Conventions/contents.asp?topic_id=257&... (about 2/3 of the way down)
However, the amendment is news to me - thank you.
The parent has a valid point. If AIS (Automtic Identification System) is being broadcasted by ships that traverse the area around Somalia, pirates could indeed decode these transmissions using a simple VHF radio and free associated software, and literally have a map of detailed locations of all broadcasting ships within about 25-50 miles of the receiver (VHF is typically line of sight)