The required service for the endorsement of able seaman—limited, qualified for limited service on a vessel on any waters, is at least 18 months’ service on deck on board vessels of at least 100 gross tons as measured under , or an alternate tonnage measured under as prescribed by the Secretary under operating on the oceans or navigable waters of the United States (including the Great Lakes).1section 14502 of this titlesection 14302 of this titlesection 14104 of this title