boats with houses

Help me out here.  I stopped by the Duxbury Harbor today because I'd never been down where the boats are.  I was curious, and I was also hoping to see some interesting birds.  

What I did see was a bunch of boats with little houses on them.  What are they? Little floating fishing cottages where you can get out of the elements? They don't look like fishing boats, and I've never seen one out on the bay.  They don't look large enough to be actual house boats.  And they're flat like barges, so they wouldn't be too seaworthy.  Are they personal docks, perhaps? To quote Ferris Bueller's Day Off, "Anyone? Anyone?"