NAHANT – Led by Greater Lynn YMCA fitness director Sharon Dobbyn, five fledgling triathletes will test their abilities for the first time July 10 during a competition on Nahant Beach.”I’ve been whipping them into shape,” Dobbyn said. “This will be their first triathlon. None of them has done this kind of competition before.”The triathletes are Tim Dwyer of Lynn, and Colleen O’Leary, Erika Olandt, Kathy McDonald and Laura Cipriano, all of Nahant.”We’ll have shirts that say Tri-US with the Lynn YMCA logo on them as well,” said Dobbyn, noting the competitors must complete a quarter-mile swim, 5-mile bicycle ride and 2.9-mile run. “The five people are in their 30s and 40s and some of them just got started exercising with this triathlon program. But most of them will do fine.”The YMCA triathlon class began in March. About 40 people are expected to compete July 10.Dobbyn, of Nahant, participated in two triathlons in one August weekend last year, one of which included a half-mile ocean swim, 3-mile run and 9-mile bike ride. The run was on sand along Crane’s Beach in Ipswich. The second triathlon was Olympic-size, with a 1-mile swim, 6.2-mile run and 26-mile bike ride.”I did it for fun,” she said. “The competition in Nahant has been going on for 25 years, and it’s just for fun, too.”