SAN FRANCISCO — As I stepped aboard the America’s Cup catamaran Luna Rossa Swordfish, a crewman handed me something not typically associated with the genteel sport of yachting: a helmet, my first clue that I was in for more than a leisurely sail around San Francisco Bay.

At $1 million apiece, and built of the same high-tech materials used in racecars and fighter jets, the racing boats in the AC45 class are among the fastest in the world — the sailing equivalent to a Formula One car. I was given the opportunity to ride along during an America’s Cup World Series race, one of many warm-up events leading to the Cup competition here next year.

The crew member Alister Richardson steadied me as I made my way across the aptly named trampoline that served as a deck to the spot reserved for the guest racer: a strip of mesh no more than 18 inches wide behind the rear beam of the boat. As I tried to settle in, Richardson knelt to explain my job, which sounded pretty simple: when the boat turned, I would shift along with it, always moving to the windward side.

Unlike the monohull America’s Cup yachts of the past, catamarans have no heavy keel below water to counteract the tipping force of the wind. With nearly the same amount of sail area as those classic yachts but at a fraction of the weight, leverage and the weight of the crew would be the only forces keeping Luna Rossa Swordfish upright — especially given the gusty conditions on this Saturday in October.