Alot of the abandoned boats that I have seen have major bulkhead issues.
Luckily, in this case the boat is not big enough to have a major bulkhead...
Legally, the marina owns the boat unless there is a current lease in effect.
Ask them to look through their leases, and their purchase documents. If there is no specific mention of the boat, or if there is no reference in the purchase agreement that they are assuming any tenancies in effect at the time of the purchase, and there is no record of a tenancy agreement for the particular boat, they own everything on the land that was there when they took possession.
Your concern would be any outstanding liens. If you are able to come to an agreement with the marina, it would be prudent to make sure that you are not assuming ownership of a boat that has a lien registered against it. Could be the case that someone had an Awlgrip job or something done that they ended up not being able to pay for...hence walked away from the boat.
If the lien is still registered then you are liable for it if you assume title to the boat.
The lien would need to incorporate the HIN or serial number or some such thing in order to be enforceable... (which is not to suggest that you should just obliterate those or anything of course....)