Anyone who cannot appreciate the America's Cup races his obviously never sailed on an America's Cup boat. The boat churns forward under the lash of the wind, the spray flies over the bow, the rigging whistles, the sails stand stiff as wings and the craft becomes a singular creature, half fish and half bird.

There is a tremendous feeling of movement both powerful and inexorable. The speed may read only 12 knots - considerable for an America's Cup boat - but what does the speed know of what sailing does for the senses?

The actual velocity is not important, it is the illusion that counts.And when these great, sleek vessels get going good, all aboard come under the influence of a sensation that is unique, wonderful and obsolutely satisfying.

Duby Joslin, a lieutenant at the Naval Academy who has earned a berth on the America's Cup boat Independence, is good at describing how sailing affects him. "There is always a feeling of enormous power," he says. "Less when we're going into the wind, but much more when we leave the windward mark and set sails for a reach. Then comes a sudden forward surge. "It's like riding a locomotive."

There is another feeling that a sailor of Joslin's experience automatically puts out of his mind but makes America's Cup boats - or any boat sailed hard - almost terrifying. It comes when a boat already heeling well is smote by the fist of a powerful gust. Then the boat sways way over, the water pours in over the lee rail and for one terrible but marvelous moment you are absolutely certain the boat is about to capsize.

Intellectually, you know that can't happen: the weight of the keel gets the boat erect again and the very act of heeling lets some of the wind spill from the sails. But beneath the coolness of reason is a tensed-up gut saying, hey, this thing is going over and it and me and everybody else aboard are going to go straight down to Davy Jones' locker.

It is true that an America's Cup boat is an expensive piece of equipment that nonsailors find easy to scorn. But they are not exclusive possessions of the very rich - as witness the periodic appeal by some boat syndicates for money from the public.

And they are not always raced by the particularly well-to-do or the especially favored For Joslin, his paperboy pennies earned him enough to buy a boat. He won races at high school, he won at the Naval Academy and he won on the big boats that race offshore. When he graduated from the Naval Academy he was sought out by an America's Cup skipper only because he had long before proved it was the kind of boat he could handle.

To be a Duby Joslin is the hope of nearly every young sailor who races on the Potomac River or Chesapeake Bay.

Sailboat racing may not be the most spectacular thing to watch so it's not going to attract a big audience. But what does Joslin care? If he can merely get out on the water for a few hours every weekend he can pretend he's on his own America's Cup boat.

That is thrill enough for him.