Town harbors in Maine are regulated by the town. The vast majority of moorings are private. Southwest Harbor is not dredged, so the Corps of Engineers rules don't apply. There are rental moorings that are clearly identified as such. In Maine, unless a mooring is identified as a rental, a guest mooring or a boat yard mooring, it is private and was placed after applying to the town normally after quite a long time on the waiting list. I am aware of the "destination" moorings you refer to. The local town will generally remove them if notified. Given the way towns work in Maine pretty much the entire coast is in one town or another. For example, most of Merchant row is in the town of Stonington.

Also, I am talking about going out for a three hour sail and finding someone on my mooring when I come back.