A US Flagged vessels must have a US Crew in US Waters. Less than 200 tons a green card is enough. If the person actually holds a captain's license then he must be a USCG licensed captain. American boat, american crew. A foreign captain can stop in any us boat with a foreign flagged boat. That foreign captain and boat cannot go to a second US port without stopping into another non us port first. Let me try again. A foreign friend who is not a licensed maritime officer might get away with moving your boat into the United States. It would be best to never get caught with a non US maritime officer running your US flagged boat in US waters. No one can ever work in the US without a green card. A foreign flagged vessels is not the US even in US waters. Every US port has foreign ships with foreign crews everyday.