Fulton Terminal, spotted at Bristol a few weeks ago, is an interesting model. And one I'd love to do a proper photo shoot on, but you can't really feature an American layout in British Railway Modelling!*
Taking to the owner, it seems that there were several rail yard in New York - each of which was unconnected to the rest of the system. They existed simply to move "reefers" between boats and warehouses. All goods went in and out by ship.
The locos would also be moved afloat, but otherwise weren't allowed near the barges the rolling stock travelled on. Not because of their weight, a loaded freight car being heavier than a loco, but because they would upset the balance of the barge when moving on. For shunting, reach cars were provided so the loco stayed on dry land.
Quite how you got a loco on board to take it to the work, is a mystery, but I guess some stock at one end to act as a counterblance would do the job. It wasn't a daily occurance, so a special shunt would be in order.
*Don't try the "Good modelling is good modelling" line. Some people go nuts if there is too much of any era in an issue. They would lose it completly if we tried to put Johnny Foreigners trains on the page.