For the purpose of this chapter, the term "Deep Draft Harbor and Terminal" means a structure, series of structures, or facility of any type located on the continental shelf off the coast designed to accommodate deep draft vessels whose draft is greater than the depths of the present United States' harbors and waterways commonly used by oceangoing traffic, and includes all functionally-related structures and facilities which are necessary or useful to the operation of the terminal whether on land or seaward of the main structure or facility.