Shy, handsome Billy, a 13-year-old ninth-grade student from Seattle, took both heats in the JU runabout class to retain his title (won last year) at National Stock Outboard Championships in Cambridge, Md. He has won or placed in 29 of his 30 races in 15 regattas this year. Billy's father, a Seattle bakery owner, his mother and three sisters (ages 17, 16 and 12) made the 3,200-mile trip to Cambridge with him.