The Hamptons Lifeguard Association has its junior and senior teams competing in the national tournament at Daytona Beach, Fla., this week, and among its competitors will be Chasen Dubs, who recently recorded four national Y.M.C.A. qualifying times at a regional short course Y meet in Naples, Fla., and Amanda Calabrese, the two-time reigning beach flags champion who represents the United States in international lifesaving competitions.