Interesting! Which kinds of ships do you want, then? Just cruise ships? Tell me a bit more about why you'd want to be notified about them.

Military, search and rescue, police boats, cable layers, fire boats, icebreakers, etc.

The sort where I could subscribe to notifications and get a few messages a day and go "huh, that is cool".

The trouble here is that AIS is a pretty blunt instrument as far as ship classification goes. If you go here and scroll down to Table 11, you'll see what they transmit: https://gpsd.gitlab.io/gpsd/AIVDM.html#_type_5_static_and_vo...

Ships like you describe are also often weirder with what they transmit. Cargo and cruise ships go from known port to known port in reasonably predictable ways. (Reasonably predictable meaning that 50 or so regexes can usually extract a little sense from what some sailor types into a bridge console.) But a lot of data from smaller, less predictable ships is much less regular.

Now that it has been running a while, I should definitely go back and see what else I can extract from the data. But one of my problems is that this stuff is poorly documented. What I really need is connections to maritime experts who can look at the data and say, "Oh, that ship is..."