Boatman has been capsized several times, but always by a wind, never by a sea.

In small boats that's the way it goes, and it's no big deal. A nasty squall comes along, and before you can douse sail it knocks you over. Then you must sit on the overturned hull and wait till the wind abates, bring the boat aright and, if you're wise enough to have positive flotation, bail out and sail off again.

Capsize of bigger keelboats is much rarer and more perilous. A keelboat by nature is extremely resistant to capsize, with the great mass of lead underwater serving as a counterweight that keeps the boat upright in all but the most severe conditions.

A keelboat may be knocked over by a sudden gust, but she'll bounce right back up. To capsize her, which is to say roll her 180 degrees so the mast points to the seafloor, takes a mighty sea in addition to wind. This being a rare occurrence, keelboats are not designed to weather capsizings and thus may be severely damaged and even sunk when they do go over.

The risks to oceangoing yachts have always existed, but the ferocious storm that capsized a number of yachts, sank five and killed 15 sailors in the 1979 Fastnet ocean race off England brought new attention to the danger.

One offshoot of that experience was the decision by the U.S. Yacht Racing Union and the Society of Naval Architects and Marine Engineers to try to expand the understanding of forces that go into capsizing an ocean sailboat.

They and other offshore racing officials are determined to take precautions so a Fastnet-type tragedy does not occur in the Newport-Bermuda race, the East Coast's major big-water event, which is held every other year.

One of the outfits that agreed to help is the hydromechanics lab at the U.S. Naval Academy in Annapolis, where naval architects Joe Salsich and John Zseleczky have been conducting capsize experiments whenever they get a break in their regular schedule of testing Navy ship designs.

They made small models of the midsections of typical oceangoing keelboats, then put them in a testing tank and subjected them to waves. The capsizings, videotaped in slow-motion detail, are harrowing to watch for anyone who enjoys a day on the water.

Salsich said the experiments showed, not surprisingly, that boats are most susceptible to tall, breaking waves when the boats lie broadside to the breakers. In these circumstances, two conditions almost ensure capsizing -- when the boat rides up the forward side of a breaker and then is thrown almost horizontally by the breaking crest, or when the boat lies in the path of the wave just after it's broken, when the break creates a powerful, thrusting wall of water.

It's horrifying to watch the way the boat is hurled a great distance by the forward motion of the wave, not simply rolled over. The potential for damage is obviously extreme in these circumstances, as the boat is flung on its side like a toy, and fragile rigging and masts can snap like thread and toothpicks.

Salsich's goal was to find ways to defend against capsize, and experiments so far have shown that a key factor in reducing the roll potential of a yacht is having the mast and rigging in place. The mast disperses weight and creates inertia, he found, which makes the boat harder to roll. But once a boat is dismasted, as can happen easily in a gale, the boat has much higher roll potential.

Thus boats with light, racing-type rigs, which are more likely to be dismasted, are particularly susceptible to capsizing. Other trends in racing-yacht design compound the problem: By keeping the keel and hull material of the boat light, as racers like to do, the weight is centered in the middle of the craft and capsize potential increases, the study showed.

The scientists did not find in preliminary studies that increased beam (width) of modern racing yachts was a factor in capsizing, and they said size and shape of the keel did not seem to make a big difference.

What really made the difference as they enacted 1,000 capsizing events in the Naval Academy towing tank was placement of the vessel in relation to the wave.

"There are certain circumstances where it doesn't matter what kind of boat it is or how well the weight is dispersed," Salsich said. "If you're broadside to a breaking wave and it catches you right, you're in trouble.""