[PaulK]

520 miles at sea is a serious enough distance to call for a serious boat.  For a trip like that in the post-apocalypse the seasoned sailors in the crew would probably want something like a Hallberg-Rassy 370 under them.  A bigger boat might be more comfortable, but with just three crew boats over 40 feet get difficult to handle. Equipment designed to allow two people to sail a 60′ boat can break, for example. What do they do then? Tired crew make mistakes, and problems snowball – despite Global Warming.