(a) Boarding and examination
Any hovering vessel, or any vessel which fails (except for unavoidable cause), at any place within the customs waters or within a customs-enforcement area established under the Anti-Smuggling Act [19 U.S.C. 1701 et seq.], to display lights as required by law, or which has become subject to pursuit as provided in section 1581 of this title, or which, being a foreign vessel to which subsection (h) of section 1581 of this title applies, is permitted by special arrangement with a foreign government to be so examined without the customs waters of the United States, may at any time be boarded and examined by any officer of the customs, and the provisions of said section 1581 shall apply thereto, as well without as within his district, and in examining the same, any such officer may also examine the master upon oath respecting the cargo and voyage of the vessel, and may also bring the vessel into the most convenient port of the United States to examine the cargo, and if the master of said vessel refuses to comply with the lawful directions of such officer or does not truly answer such questions as are put to him respecting the vessel, its cargo, or voyage, he shall be liable to a penalty of not more than $5,000 nor less than $500. If, upon the examination of any such vessel or its cargo by any officer of the customs, any dutiable merchandise destined to the United States is found, or discovered to have been, on board thereof, the vessel and its cargo shall be seized and forfeited. It shall be presumed that any merchandise (sea stores excepted), the importation of which into the United States is prohibited, or which consists of any spirits, wines, or other alcoholic liquors, so found, or discovered to have been, on board thereof, is destined to the United States.

(b) Unexplained lightness of vessel or discharge of cargo
If any vessel laden with cargo be found at any place in the United States or within the customs waters or within a customs-enforcement area established under the Anti-Smuggling Act [19 U.S.C. 1701 et seq.] and such vessel afterwards is found light or in ballast or having discharged its cargo or any part thereof, and the master is unable to give a due account of the port or place at which the cargo, or any part thereof, consisting of any merchandise the importation of which into the United States is prohibited or any spirits, wines, or other alcoholic liquors, was lawfully discharged, the vessel shall be seized and forfeited.

(c) Vessel bona fide bound from one foreign port to another foreign port
Nothing contained in this section shall be construed to render any vessel liable to forfeiture which is bona fide bound from one foreign port to another foreign port, and which is pursuing her course, wind and weather permitting.