Sea water corrosion coating

I am looking for a coating that can be used on ocean based structures, like oil drilling platforms. The substrate would be steel, the life requirement is 30 years, and I am told inorganic type coatings are peferred (but I would welcome any ideas). It can be applied on shore, not necessarily after construction. Does anyone have any ideas for 30 year coating life in seawater? I think something like 20 mils of Naval Spec paint is already being considered.