Вот это я не знаю, обычно 6 месяцев, но насколько проверяют не в курсе.
Вот что пишет Роял
Royal Caribbean International strongly recommends that all guests travel with a passport that is valid for at least 6 months beyond the end of the cruise.
Но это рекомендация, а не закон. Подозреваю, что ничего не будет.
Вот, кстати, со странички Норвегов
Alien Residents of the United States holding an Alien Registration Card (ARC or "Green Card") (Form I-551) may travel to Canada, Mexico, Bermuda (see Visa Restrictions on Bermuda) and the Caribbean with just their valid ARC and Proof of Identity. However, it is recommended that these guests also carry their passports from their country of citizenship if available. In some instances, ARC holders may still be required to have sailing permits and/or visas to enter countries Norwegian Cruise Line visits in these areas. Please note that travel anywhere else in the world requires a valid passport from the country you are a citizen of and subsequently subjects you to any documentation, visa and health requirements of all countries visited.
А вот для Бермуд точно нужно 6 месяцев
NOTE: Guests who require a visa for travel to Bermuda who have the right to reside in the U.S. (ARC holders) or Canada (Landed Immigrant status) who possess proof of such status AND have a passport that is valid for at least six months after the last day of the cruise, will not require the Bermuda entry visa.
Для Карибов не указан срок действия паспорта лишь бы был действительным.
RCI: Diamond 16 cruises (137 nights)~NCL: Platinum 9 (76)~Princess: Platinum 7(57)~Celebrity: Elite 6(44)~HAL: 2(14)~Cunard: 1(5)~MSC: 2(14)~Carnival: 3(19)
Future: Anthem x 3, Oasis x 2, Adventure