Every commercial vessel and some large pleasure craft transmits it's position and vital statistics using AIS. Using this data and images from the shipping news page we can show you the position, and if we have it a picture, of every vessel on the bay. You can also see what 30 days of cumulative traffic looks like and see an animation of a days traffic or view the current map fullscreen.
The map updates every 15 seconds if you watch you'll see the ships move!
Special thanks to GeoGarage for the very cool NOAA charts map layer.
This map is not for navigation, but then you knew that