This makes no sense! Over 200 years ago in international waters?
Sure it does. War ships remain the property of the nation in perpetuity.
There are no salvage rights for warships.
Now on the other hand an argument I have thought about is that; is the Royal Spain actually the same nation as the Republic Spain?
If at any time the Republic Spain repudiated any debts incurred by the Royal Spain I think an argument could be made that they are not the same and the nation that was owner for that ship no longer exist and the ship is salvage.