Sometimes you can find a boat and trailer where the owner just wants everything gone. Usually there are no papers. So you get a trailer and a boat that now you have to get rid of. In NY it is difficult to get rid of a boat except for some outfits who will cut it up and put in in dumpsters and that is expensive. In addition you have to remove all fluids and tanks. You may need to pull the motors too. Bottom line is that it isn't a deal even for free. Other states may have easier ways to junk a boat.
At one time years back, one of the NYC Sanitation dumps was taking boats for a small fee but you had to have a signed over registration.
In the past it was somewhat common for owners looking to get rid of a hull to intentionally sink them. NY had so many sunken hulls washing up that they started to salvage them and get the HIN number. That led them to the previous owner who then got a VERY expensive fine for illegal dumping
