You won't give up will you?
"Right of finds" as you put it applies only to items that can not be positively identified by the party that lost the item. And it your case it cannot apply, the boat had identifying numbers. Right of finds would apply if you found a bag of money, if no one could show proof that the money belonged to them, you would get it. And as I stated in my previous post, salvage rights have specific laws that apply. And you have not stated the reason the vessel was adrift on the ocean shoreline. It could have been stolen and scuttled, used in the commision of a crime, or lost due to a storm. But finders keepers does not apply in this case. You should check out the reason the vessel was abandoned. You may be able to acquire the boat for a small cost.