America's cup. US supremacy in world's premier yacht race faces serious challenge from Australian boat

Now is the time for all good American sailors to prepare for a keelhauling! It commences Sept. 13 when a mystery keel is expected to help Australia beat the barnacles off the United States in a best-of-seven racing duel known as the America's Cup.

The Cup, a cherished silver goblet prized in world sailing, has never been lost by the United States in 24 challenges over 132 years. This may be the year.

If the Cup doth run Down Under, to the very avid sailor it will be the diplomatic equivalent of Japan winning the World Series or a Russian winning the Masters golf tournament.

When Britain lost the cup in 1851 off its own shores, it was no small coincidence of history that Britannia's rule of the waves began to waver.

During that race, as the yacht America was winning the goblet for the New York Yacht Club, Queen Victoria asked who was in second place.

''Alas, Your Highness, there is no second,'' she was told.

In 1983, alas, there is still no second, and the New York Yacht Club (NYYC), as defender of the longest sports monopoly in history, has tried to win the Cup this year both on the waves and by the rules.

Plenty of embarrassment was brought upon the blue-blood, blue-blazer - and now red-faced - denizens of the NYYC. In three months of trial heats this summer , the ''men in straw hats,'' as they are called, tried to (1) copy, (2) buy, and (3) protest the legality of the unorthodox, winged keel at the bottom of the Australian yacht.

It was like Yankee baseball manager Billy Martin yelling ''pine tar!'' after an opponent hit a winning home run with a gooey bat.

The NYYC actions showed to what lengths rich patrons and competitive yachtsmen with their pricy toys will go to win a game when honor is at stake.

On the streets of Newport, Cup watchers could be heard explaining to foreign guests: ''Don't think all Americans are like that. That's just the New York Yacht Club.''

The Australians, meanwhile, have been shrouding their finned keel after every race, hoisting their white vessel out of the water behind green plastic, and posting a 24-hour guard. It's a great stunt as well as an intangible edge.

Rumors flew around Newport that a picture of the keel could bring $10,000. One member of the Canadian team got caught wet-handed trying to photograph the keel from underwater at the pier.

The Aussie keel, a Star-Trekian fin attached horizontally to the vertical plate under the hull, was a . . . well, a 'roo awakening for the NYYC.

How could a non-Yankee come up with a technological breakthrough in sailing, after almost every American boat designer assumed hull shapes had reached a pinnacle of speed during the last decade?

The design should not have caused shockwaves. There are too many parallels between the two nations. Australia, like the United States, is an ex-British colony loaded with sea-faring, individualistic, competitive, and imaginative people.

''He who dares, wins,'' says Australia II manager Warren Jones.

On top of that, the Aussies have two decades of Cup challenges under their cap. Each challenge comes every two, three, or four years - depending on the preference of the NYYC - and the last four Australian challenges have been led by Alan Bond, who finds the publicity useful for his real estate and energy business based in Perth. If Bond wins, the next Cup will be held in Australia.

Under the International Rules of Measurement for the Cup, the dimensions of a proper yacht are almost pre-fixed under a rule known as 12-meter - which stand for the equations involved and not the length of the boat (usually 63-plus feet). Such standards help equalize the boats so that seat-of-the-pants sailing ability becomes the ultimate test.

Just the same, innovations do come along, and it is still largely the quality of materials, especially sail cloth and its cut, that often make the difference on the triangular, 24.3-mile course of the Cup races.

Since the last Cup contest in 1980, when the US boat Freedom beat Australia 4 -1, the rules have been changed to allow foreign challengers to use American know-how and sailing materials.

Two Du Pont synthetic materials, for instance, known as Kevlar and Mylar, are now common on all 12-meter sails. The strong fibers hold the shape of the sail in both soft and stiff breezes. (The Kevlar turns brown in the sun's ultra-violet rays, giving the sails a two-tone color.) Also creeping on board are American computers, which tell crews everything from boat speed to sail choice.

If the NYYC's selection for defending the Cup, the red-hulled Liberty, happens to beat Australia II, it means tactics, crew precision, and cut of sails still count for something, despite the keel innovation.

Also, the Americans are playing in their own ballpark. They know the flukiness of the winds and the strange tidal currents.

But the Aussies after numerous challenges must know how to read the spindrift off Rhode Island Sound. They also have tried to give themselves as much practice as the Americans. US boats have always had more competition in the months leading up to the final races. Liberty had to beat out not only its own stablemate, Freedom, but also Courageous and its stablemate, Defender.

Courageous, the sentimental favorite after winning the Cup in 1974 and 1977, almost took the defender slot from Liberty. But Dennis Connor, a San Diego drape maker who was the 1980 skipper on the winning Freedom, put together the best American team, from bowman to navigator. Like other 12-meter teams, the Liberty crew practiced for over a year, living together in a Newport mansion all summer, rising early for joint exercise and meals. The sailors are the cream of American yacht racing.

Alan Bond's campaign, which has been running almost continuously since 1974, found itself up against six fellow foreign challengers this year: two other Aussie boats, Advance and Challenger 12; Britain's Victory '83; Canada's Canada 1; France's France 3; and Italy's Azzurra.

Some sponsors take as much spotlight as the boats: Canada is backed by a Calgary ''cowboy,'' oilman Marvin McDill. Bahamian financier Peter deSavary is behind Victory '83. French filmmaker Yves Rousset-Rouard (''Emmanuelle'') funds France 3. And the Italians, strangely enough, are financed by the Aga Khan, the wealthy religious leader of 15 million Shia Ismaili Muslims.

In all, an estimated $48 million has gone into both the defense and challenge of this year's Cup races.

The fins are the revolutionary idea of Australian boat designer Ben Lexcen, who says he has been toying with the idea since the early '60s. Other than that, he is not talking.

According to Jerome Milgram, an ocean engineering professor at the Massachusetts Institute of Technology, the keel is an innovation. He likens it to the wings of a U-2 spy plane, whose long wingspan helps reduce wing drag.

''The fins help remove the vortices (eddies) flowing around the keel,'' says Dr. Milgram, who recently conducted a series of tank-testing on 12-meter designs , and who was professor to Australia II skipper John Bertrand.

Australia II's speed may not be any faster than Liberty's, says Dr. Milgram. But the keel is thought to allow the boat to tack back and forth faster when heading into the wind - perhaps almost four seconds faster than Liberty.

That can make all the difference in the Cup's unique form of match racing (one on one). The boat that gains the lead at the start can keep it by staying just ahead of the other boat. This blocks the full force of the wind, preventing the following boat from reaching full speed. To maintain this wind ''shadow,'' the lead boat tacks whenever the other boat does.

Thus, the America's Cup is known for the precision of its tacking duels, testing how well a crew brings the sails from one side to the other while the helmsman turns the boat into the wind.

If one boat can tack just a split second faster than the other, it can eventually take the lead.

Although the fins have not been revealed, it is assumed that when the boat heels in a breeze, the fins turn slightly vertical. This helps the craft from being pushed sideways.

But the keel may have disadvantages, says Dr. Milgram, such as stalling the boat a bit as it finishes a tack, forcing the helmsman to point the boat less directly in order to catch more wind. Also, in high wind and heavy water, the fins could slow down Australia II as the boats bounces more.

These disadvantages may, in the end, cause the fins to boomerang on the Australians.