But then you would have large boats driving through the streets for a bit so it’s a loose loose unfortunately. Like I say it’s because Open Street Maps (which the game uses for the pathfinding) only makes the sea a texture rather than a specific texture so unless there is a ferry route, there would be no routes for the game to use.
Honestly haven't gotten as far as the large boats yet so I wasn't thinking of them and/or how they are used. I assumed the fireboat and rescue docks were built on ocean coastlines though am I wrong? Using the same logic as above you can just disable the ability to travel via roadways and ONLY have them travel via ocean or defined water waterways (using the POI system). This would of course make them more realistic, at least in that one regard of them traveling across land, but at the same time make some missions not accessible by large boats if people are not careful where they place their docks and where they set the POI's that trigger ocean missions (making sure they are actually accessible by the ocean or large water way).
Not familiar with Open Street Maps either but with what little researching I did they do have a tag system they could be utilized to ensure it would work. But then we start getting into an issue of time spent compared to results achieved as it wouldn't be a quick thing to do. In short it's still very much doable but I doubt the dev. team are willing to spend the time to do it for such a small outcome.