If your neighbor tells you he can walk on water, wait a sec before dialing 911. He just may be one of the thousands of ordinary Americans who are discovering the rush of treading where no human has trod before. All it takes is an open mind, an adventurous spirit—and a Hydro Bronc, an inflatable spheroid that looks like the world's largest hamster wheel. "Man, I had a blast," says Brian Trescott, 23, a rafting guide who recently tried it on a gnarly stretch of the New River in Fayetteville, W.Va. "I didn't get out of that thing for five hours."

Inspiration for the Bronc came a few years ago to Rod Blair, a Bakers-field, Calif., inventor, during a white-water rafting trip. Looking on anxiously as an inflatable boat smashed brutally into a rock, Blair, 47, an engineer who holds a half-dozen patents, started thinking, "How could you make this safer?"

The design he perfected in his backyard pool—-and that his son Luke, 21, tested on numerous rivers and in treacherous Class 6 rapids—uses a system of puncture-proof polyvinyl bladders weighted so that, when the unit tips on its side, it quickly rights itself. Once strapped into the waist harness, nearly anyone can propel the Bronc forward in calm water; only the highly fit can confront raging rapids.

This summer a handful of the $3,000 devices are in use at several resorts. Blair and his partner Philip Chauvet are hoping full-fledged Broncmania will break out next year, when SAM's Club begins selling them on a limited basis. But by then Blair plans to have put the Hydro Bronc to another test. "Waterfalls," he confides. "We've found a 30-footer in Mexico that looks perfect."

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