Wind and waves would be a problem as they'd push the train around and it'd be hard to control with a tug. I think it'd be less hydrodynamically efficient too wh

Wind and waves would be a problem as they'd push the train around and it'd be hard to control with a tug. I think it'd be less hydrodynamically efficient too which would mean higher fuel costs overall: assuming you could build a single large ship with the same capacity as the train then it'll have a lower surface area => lower drag.