46 USC 12131 - Command of documented vessels

(a) In General.— 
Except as provided in subsection (b), a documented vessel may be placed under the commmand[1] only of a citizen of the United States.
(b) Exceptions.— 
Subsection (a) does not apply to
(1) a vessel with only a recreational endorsement; or
(2) an unmanned barge operating outside of the territorial waters of the United States.
[1] So in original. Probably should be “command”.