Every year, toward the beginning of July, the waters of Zamami Island — so blue as to seem synthetic — are disturbed by a fleet of yachts. Almost 60 in number, the yachts cut elegant figures across the ocean, their hulls heeling and sails billowing as the prevailing south-westerlies drive them through Kerama Shoto National Park. They are in competition, each vying for position before reaching the finish line of the Zamami Yacht Race.