26 U.S.C. § 4472

1. (1)
   1. (A)The term “covered voyage” means a voyage of—during which passengers embark or disembark the vessel in the United States. Such term shall not include any voyage on any vessel owned or operated by the United States, a State, or any agency or subdivision thereof.
      1. (i)a commercial passenger vessel which extends over 1 or more nights, or
      2. (ii)a commercial vessel transporting passengers engaged in gambling aboard the vessel beyond the territorial waters of the United States,
   2. (B)The term “covered voyage” shall not include a voyage of a passenger vessel of less than 12 hours between 2 ports in the United States.
2. (2)The term “passenger vessel” means any vessel having berth or stateroom accommodations for more than 16 passengers.