Car/vehicle entities aren't really setup to work with fluids, but trains are: maybe make a rail/track entity placeable over water, but not land, with a transparent graphic with translucent dotted lines to indicate the route ... then a train entity that looks like a ship, and a station entity that looks like a dock, and a then you could automate routes using rail automation and use something like the fluid wagon. Automated Ship! Tricky part would be that trains have to have both the train engine, and the wagon to be useful ... not sure if you can make a train engine entity that can also hold cargo/fluids ... sounds like a new mod :D
