Re: Courtesy Flags
As to the British captain on the U.S. boat, the "nationality" of the boat is what determines proper etiquette. A U.S. boat will show the U.S. flag, regardless of who's at the helm, and entry requirements would also be in accordance with the country of origin of the vessel. Entry requirements for individuals on board would be governed by whatever agreements exist between someone's home-country (e.g. passport issuer) and the destination country.