More likely NEMA2000 which is on CAN, as opposed to serial (not RS232, but only an electrical engineer can understand the difference). CAN vs serial requires different message formats, but the difference is irrelevant if you don't have to implement it. (I've personally had to implement both)

Surprisingly much of the commercial style SOLAS equipment still sadly runs on NMEA 0183. It is a real hassle if you have a split system with some converters not liking each other, different baud rates for "high speed(!!!)" and so on. Ugh. Been there done that.

Like the Sailor 6222 Class A GMDSS VHF which is found in loads of commercial vessels and still is their "newest" model. That only accepts NMEA 0183 inputs.

I wouldn't be surprised if that "much" was "most." I did a couple of small projects for a commercial fishing vessel a few years back to ingest NMEA0183 sentences and convert them to an AIS message (I think he was connecting it to a newer chart plotter that only had AIS input).

I recall asking if this functionality wasn't available off the shelf and the answer was that it existed, but it was difficult without also buying a lot of new equipment he didn't need. It apparently cost a lot less to have me do the data conversions (and I didn't charge much for it) on a small SBC than it would to have to buy new equipment and deal with installation, fitment issues, etc.

Agreed. these ships are full of electronic sensors... but the tech installed the AIS transponder what did he use for heading? the ship gyro or one of the dozen gps receivers installed. This was not well defined and sloppy. Nobody asked questions..you just wanted to be compliant. They were not initially thrilled about being constantly tracked. Ideally always use the GYRO.. dont complicate life using GPS heading. If the gyro is out the ship is anchored most likely.