Hangingfor8,
The limit for US waters is definitely 24 nm off shore. Within that distance, it is US waters, and the rules are exactly the same as within 12 nm. The first 12 nm is the territorial limit, increased from 3 nm by one of Reagan's Presidential declaration, the next 12 nm is the Contiguous Zone established by one of Clinton's Presidential Declarations. Not every country has established a Contiguous Zone, but they all have the right to do so.
And outside of the 24 nm limit, you do need authorization from an appropriate federal court in order to salvage a wreck. Just because it is in International Waters does not mean there are no rules. Beside, as Darren says, you would want to protect your rights, either with the aid of the law, or with the help of one of Chagy's friends, apparently!
Mariner