JOAN THAYER can't remember a time when she didn't sail. "It's all I do," she says. And since elementary school, Ms. Thayer has been racing one-design sailboats in the Marblehead (Mass.) Race Week, the oldest yacht-racing event in the country.In a one-design race, the competition is among boats of identical design - usually 30 feet or less. Unlike the Performance Rating Handicap System (PRHS), where large boats with paid crews race with handicaps against time, one-design boats race against each other. So even when there is no wind, whoever crosses the finish line first wins. "It's your grass-roots sailor," says Thayer. This year, race week's 102nd anniversary, there was no wind, only an approaching storm. A power boat glided among various one-design sailboats - Etchellses, International One Designs, 210s, and Shieldses - and offered their skippers a tow into shore. The sailors too tired to try getting there themselves took up the offer. Those too proud for a tow declined and headed listlessly toward land. Despite its name, race week does not last an entire week, though once it did. Now, for four days each year at the end of July, racers come together to sail "the purest kind of sailing there is," as a devoted one-design racer says. For the first decade of the event, there was no such thing as a one-design boat. Since the turn of the century, both race week and the boats that race there have had to contend with the changing times. Race week, for instance, is no longer the only regatta of its kind. It now c ompetes with hundreds of similar events, many of them sponsored by large corporations. The popularity of one-design racing, meanwhile, has leveled off in the past decade, despite the comparatively low cost. Bob Kosty, chairman of this year's race week, says that it's a national trend, not a local one. "It has to do with how people conduct their lives," he says. With one-design racing, there is usually a small crew and a large time commitment. "People have so many other choices [besides sailing] today that they often don't want to make the commitment," he says. Still, the devoted one-design racer cannot be swayed. According to Thayer, a native of Marblehead, most people make a choice between one-design racing and PRHS racing, where the boats are larger and the crews bigger. "In my boat there are four of us," says Thayer. "We go out there and bring our own lunches; I supply the beverage, somebody else brings the apples or carrots. At the end of the day, we go home and the next day we come back and do it all over again." Thayer works full-time as an investment banker, in addition to holding volunteer sailing positions. Along with other sailors who love one-design racing, she's committed to do all she can to keep it going. "I love the sport and I want to give something back," she says. Economics is working in her favor. One-design boats, while not cheap, are far less expensive than their larger PHRS cousins. A boat in Thayer's Shields class, for example, costs around $18,000 new. Many of the smaller boats, she says, cost about $8,000. For people like Bob Jackson, who consider themselves "average" sailors, the low cost keeps one-design racing accessible. Mr. Jackson's racing class, the Corinthian, is considered the "family class." Jackson paid $3,500 for his Corinthian and, though he admits he is "not in a fast boat or a hot boat," he says the competition is good. But he worries about the younger generation of sailors, many of whom prefer larger, more sophisticated boats. "It drives me crazy," he says. "Some of these kids depend on all that equipment and don't even know how to make a boat go fast." This is not true for all the kids at race week. According to chairman Kosty, the junior program is one of the best things about the event. One of the largest racing lines is devoted to the 18-and-under sailors in their Flying Juniors, Widgeons, and one-person Optimists. Anything can happen when these kids race, says Kosty. "They get seasick, things break, but they love it." Norm Cressy, a sailmaker and a race-week participant since 1948, says that kids may not sail all summer, but they'll come to race week. "This is their national championship," he says. At the end of the second day of race week, after the J-24s, the Sonars, the Rhodes, the 210s, and the Corinthians all dropped anchor and rain began to fall, the one-design racers - from the eight-year-old dinghy racer to the world-class yachtsman to the 40-year veteran - stood under the yacht club tent talking of the day's successes, bemoaning the lack of wind, and already looking forward to the 103rd race week next year.