Justice Breyer’s opinion includes an appendix of the “floating home” (don’t call it a “vessel”!) in Lozman v. Riviera Beach. Here is how Breyer describes it:

In 2002 Fane Lozman, petitioner, bought a 60-foot by 12-foot floating home. App. 37, 71. The home consisted of a house-like plywood structure with French doors on three sides. Id., at 38, 44. It contained a sitting room, bedroom, closet, bathroom, and kitchen, along with a stairway leading to a second level with office space. Id., at 45–66. An empty bilge space underneath the main floor kept it afloat. Id., at 38. (See Appendix, infra, for a photograph.) After buying the floating home, Lozman had it towed about 200 miles to North Bay Village, Florida, where he moored it and then twice more had it towed between nearby marinas. In 2006 Lozman had the home towed a further 70 miles to a marina owned by the city of Riviera Beach (City), respondent, where he kept it docked

I also liked this discussion of what a vessel is, replete with a Disney reference:

Not every floating structure is a “vessel.” To state the obvious, a wooden washtub, a plastic dishpan, a swimming platform on pontoons, a large fishing net, a door taken off its hinges, or Pinocchio (when inside the whale) are not “vessels,” even if they are “artificial contrivance[s]” capable of floating, moving under tow, and incidentally carrying even a fair-sized item or two when they do so.