Hello Stu,
There is a UN Convention on the Law of the Sea agreed by most maritime countries, and also multilateral agreements indeed. SOLAS, traffic separation schemes, drugs, arms control and surveillance of fishing are not heavily discussed matters, but the commercial and judicial sides (insurance, wreckage, pollution costs, ...) are more confused and need a true expertise. These sites can lead to more infos (thank you Google).
http://www.armscontrol.org/act/2004_06/Panama.asp
http://www.oceanlaw.net/texts/losc.htm
Regards,
Luc