19 CFR § 4.60 - Vessels required to clear.
(a) Unless specifically excepted by law, the following vessels must obtain clearance from CBP before departing from a port or place in the United States:
(1) All vessels departing for a foreign port or place;
(2) All foreign vessels departing for another port or place in the United States;
(3) All American vessels departing for another port or place in the United States that have foreign merchandise for which entry has not been made; and
(4) All vessels departing for points outside the territorial sea to visit a hovering vessel or to receive merchandise or passengers while outside the territorial sea, as well as foreign vessels delivering merchandise or passengers while outside the territorial sea.
(b) The following vessels are not required to clear:
(1) A documented vessel with a pleasure license endorsement or an undocumented American pleasure vessel (i.e., an undocumented vessel wholly owned by a United States citizen or citizens, whether or not it has a certificate of number issued by the State in which the vessel is principally used under 46 U.S.C. 1466–1467 and not engaged in trade nor violating the customs or navigation laws of the United States and not having visited any hovering vessel (see 19 U.S.C. 1709(d)).
(3) A vessel of less than 5 net tons which departs from the United States to proceed to a contiguous country otherwise than by sea.
(c) Vessels which will merely transit the Panama Canal without transacting any business there will not be required to be cleared because of such transit.
(d) In the event that departure is delayed beyond the second day after clearance, the delay must be reported within 72 hours after clearance to the port director who will note the fact of detention on the certificate of clearance and on the official record of clearance. When the proposed voyage is canceled after clearance, the reason therefor must be reported in writing within 24 hours after such cancellation and the certificate of clearance and related papers must be surrendered.
(e) No vessel will be cleared for the high seas except, a vessel bound to another vessel on the high seas to—
(1) Transship export merchandise which it has transported from the U.S. to the vessel on the high seas; or
(2) Receive import merchandise from the vessel on the high seas and transport the merchandise to the U.S.