Salvage law is NOT a matter of "finders/keepers" or "let's go shopping at no cost for anything we find on the beach". Many folks have an incorrect view of salvage law and think any vessel without an owner on board is fair game if it appears to be abandoned. Not so.
In general, salvage in the U.S. is a governed by the admiralty laws of the federal courts, and provides compensation to professionals or other mariners who provide assistance to a vessel in peril, thereby saving the vessel or her contents from loss. A key element of salvage is the requirement that the property be restored to the owner.
There isn't a fixed schedule of payments, although most salvage claims are worked out by agreement after the fact. If not, then the salvor is entitled to file suit in federal court and have a judge fix the amount of compensation he is entitled to, normally a percentage of the value of what was rescued, with consideration to factors such as how imminent the peril was, whether the salvor risked his own life or vessel in making the salvage, how dire the conditions were, etc. The law usually tends to make an "ample" award in suitable cases.
There is no more right to go aboard a vessel that has foundered and to lay claim to the vessel or its contents than there is to "salvage" a Porsche parked on the side of the road while its owner gets a flat tire repaired or a can of gasoline to continue his trip. In the old days such conduct along the shore was known as piracy, and today it is simply theft. I'm not sure why so many folks think the rules differ on the road and on the sea, but in this instance they are wrong. If you do lay claim to such a vessel, you are obligated to make good efforts to find the owner (how hard can it be in an era of State registration or US documentation?) and your claim then must be taken up with him based on the benefit you conferred by your labor.
Here's a nice little article for those of you interested in more details about salvage law: Safe/Sea Online