AIS is initially intended to help ships avoid collisions, as well as assisting port authorities to better control sea traffic. AIS transponders on board vessels include a GPS (Global Positioning System) receiver, which collects position and movement details. It includes also a VHF transmitter, which transmits periodically this information on two VHF channels (frequencies 161.975 MHz and 162.025 MHz – old VHF channels 87 & 88) and make this data available to the public domain. Other vessels or base stations are able to receive this information, process it using special software and display vessels locations on a chart plotter or on a computer.
If you like tracking ships or just like being nosey, you can use the Marine Traffic website to do just that. You can move around the map and zoom in on your area and see what commercial traffic is there, what direction it is moving and at what speed is it moving. Living on the Delaware River, I often see commercial ships that I wonder about so I just look them up real time as they pass by. Use the following link to visit the Marine Traffice site. http://www.marinetraffic.com/ais/default.aspx?level0=100