I'm not sure how it would work for those boats abandoned on the water
but I know my marina has given away abandoned boats in the past. I'm not sure of the exact procedure but a marina operator might be able to tell you. Some years ago there was an abandoned Columbia
26 in the do-it-yourself yard. The owner of the yard told a fellow if he would get it out of there, he could have it. The guy completely stripped it inside and out, did some fiberglass repairs
to the hull
and rebuilt the interior
using a bunch of stuff from the nautical flea market. They found an old abandoned set of bimini
bows and his wife sewed up a new bimini
and sail cover
. All in all he spent about $400 plus sweat. A year later he sold it for $4k. Now it seems to me that he couldn't have sold it without a clear title. Somehow there was a procedure that the marina could follow to seize the boat (for back bills) and obtain title that they were able to pass on.
Since no municipality wants their waterways cluttered up, I would think they would bend over backwards to have you take over one of the derelicts. For that matter, Wooden Boat magazine usually has a section in its classifieds of boats that are free to a good home. That is, of course, if you don't mind a wooden boat.
By the way, the guy with the Colombia
named her "Lil' Repo".