Train ferries.

          If you have an interest in both model railways and model boats, here's just the model for you - a train ferry.
          In the late 19th century, the only way for rail vehicles to cross the Detroit River was a train ferry. One of these would make a realistic and relatively simple model to build. Their decks were flat with neither sheer (the rise towards bow and stern) nor camber (higher at the centreline than at the sides.) The hull could be in the shape of a scow, a rectangular box with flat sloping ends.
          The early vessels were invariably side-paddle, so no need to cut holes below the waterline for propeller shafts. Later vessels were propeller-driven.
           The superstructure was also simple. There were deckhouses either side, typically quite long on the paddlers, incorporating the paddle boxes. The top of the paddle boxes would be curved, but the rest of the deckhouses were flat, with a few cutouts for windows and doors.  The propeller-driven versions had small deckhouses, presumably they were simple shelters for the crew.
          The wheelhouse, or houses, was a simple cabin mounted on top of a gantry. This sounds complicated to make but could be pieced together from kits of suitable model railway trackside structures.
          Some vessels were double-ended, with wheelhouse, rudders, and propellers if fitted, at each end, and some single-ended. There were vessels built with 2, 3 or 4 tracks. Some were long enough to hold a string of freight cars, some only two passenger cars.
          Finding suitable rail vehicles and structures for such a model is relatively easy. If you don't want to purchase new, you can find lots of used items at most model rail shows and flea markets.

Nautical lore and a suitable subject for a model - Train ferries.