33 U.S.C. § 1203: Radiotelephone requirement

every power-driven vessel of twenty meters or over in length while navigating; every vessel of one hundred gross tons as measured under section 14502 of title 46 , or an alternate tonnage measured under section 14302 of that title as prescribed by the Secretary under section 14104 of that title, and upward carrying one or more passengers for hire while navigating; every towing vessel of twenty-six feet or over in length while navigating; and every dredge and floating plant engaged in or near a channel or fairway in operations likely to restrict or affect navigation of other vessels— The radiotelephone required by subsection (a) shall be carried on board the described vessels, dredges, and floating plants upon the navigable waters of the United States, which includes all waters of the territorial sea of the United States as described in Presidential Proclamation 5928 of December 27, 1988 . receive radio marine navigation safety warnings; and engage in radio communications on designated frequencies with the Coast Guard, and such other vessels and stations as may be specified by the Secretary.”