Roger,
Two inches in N Scale is, of course, 26.66 feet. That amount of "freeboard" (or height of deck above water) puts this float well into the "ship" category. My biggest freighters have a freeboard of about 1.5 inch, with a maximum of perhaps 2.25 inches at the bow (i.e., they are "swept" from bow to stern, not flat). The working deck of a car float would be flat. The car float images I've managed to find show a freeboard of between 6 and 10 feet. I suggest you consider this a ship, with a different set of design rules and details.
Or raise the water considerably.