Bill of Sale (Boat) with warranty
A document given by a seller to a buyer stating that on X date, at Y location, for Z amount of money, the seller sold the buyer a boat. The bill of sale can be used as evidence of the ownership change. Because this is a document with a warranty, the seller also swears (i.e., warrants) that it owns the boat. If this isn't true and a third party comes to claim the boat, the seller promises to reimburse the buyer for any losses it experiences as a result.