In an old velvet mill in the picturesque New England town of Mystic, Connecticut, there’s an unassuming door marked “Brooms.” But instead of a dusty collection of mops and buckets, anyone who opens that door will find hundreds and hundreds of boats, from ancient canoes to postwar motorboats. Together, they make up part of Mystic Seaport Museum’s historic watercraft collection, one of the largest in the United States. Because of its location on a sheltered estuary with easy access to the Atlantic Ocean, the Mystic area has always been ideal…