Chased down this Tourist boat in the S.F. Bay Area.
I'm finding out a few things about this Sea Traffic Plug-in by Marginal.
First thing is that there doesn't seem to be a large variety of types of ships/boats.
The second thing is that on replay, the ships and boats are not there, but are somewhere else.
So if you fly around a vessel and then go back to see it on replay, in hopes of a nice screenshot or for a better view of the vessel, you'll be dissapointed to find it's no longer there. The plug-in is random location, on established sea routes, in live or replay.
Screenshots have to be done on the fly, literally. (Pause button)