The frostbite season at Severn Sailing Association in Annapolis opened Sunday in perfect conditions. Seven of us had a good old time bashing our slender, 27-foot Solings around in 12 to 18 knots of wind on a breezy winter afternoon.

You had to laugh to think the same conditions are giving conniptions to the finest sailors in the world racing the world's most expensive 80-footers in the Southern Hemisphere summer.

Yes, we're talking about the America's Cup challenger series in Auckland, New Zealand, where on Sunday, Dennis Conner's Stars & Stripes joined the crowd in the infirmary. Sailing in 10 to 12 knots of breeze, the $4 million Stars & Stripes opened up like a sardine can when a rear bulkhead parted from the hull during pre-start maneuvers. The deck behind the helm "folded up like a tin can," said Conner, the world's most experienced Cup skipper.

Stars & Stripes withdrew from its race against fleet leader Prada and headed for the shed, where it's been ever since. Conner won a 48-hour reprieve to get it fixed by Wednesday or start forfeiting races. Repair crews are working around the clock but "it's going to be tight, real tight," said crew boss Bill Trenkle.

In less than two months, the Cup has had one near sinking, when the New York Yacht Club's Young America folded like a banana in 18 knots of wind last month, a withdrawal as the Swiss boat Fast 2000 quit over the weekend after a series of breakdowns, and some spectacular dismastings.

Skippers whine endlessly about mysterious cracks and bangs from the carbon fiber hulls when the wind gets up, and even have rules to delay racing in the challenger series if the breeze exceeds 17 knots for five minutes before the start. Hmmm, 17 knots. Isn't that when sailing gets good?

But for all its flaws, the racing is starting to get interesting. On Monday, San Francisco entry AmericaOne managed to hand the Italian boat Prada its second defeat of the season. The 23-second win put AmericaOne just one point behind Prada in the quest for first place among challengers.

The top six challengers advance to semifinals Jan. 2 and the field is beginning to take shape. Prada and AmericaOne seem sure to make it, along with Dawn Riley's team on America True and the Japanese entry Nippon, undefeated since unveiling a new boat--named Idaten after a Japanese god--for this final round robin.

Three boats are on the bubble for fifth and sixth place: Stars & Stripes, Young America and Spain. Stars & Stripes looks like the odd one out if Sunday's breakdown cannot be quickly set right.

Semifinals will narrow the field to two boats, which square off in late January for the right to race Team New Zealand in a best-of-nine series for the Cup in February.

Even after its loss Monday, Prada is "still the best team in my book," said AmericaOne skipper Paul Cayard. "They are sailing really well and today we were just fortunate we were able to get a race off them."

AmericaOne trailed all day but slid by for the win when Prada skipper Francesco de Angelis took a penalty turn just before the finish. Prada had clipped AmericaOne's stern in pre-start maneuvers, knocking a chip from the Italian boat's bow. Cayard protested and on-water umpires ruled the collision was de Angelis's fault.

Prada subsequently rounded every turning mark on the 18-mile course ahead but AmericaOne kept it close, staying anywhere from 15 to 37 seconds behind. That proved crucial as Prada carried the burden of a penalty spin for the pre-start infraction. De Angelis waited until the very end and was making his turn when Cayard whooshed past for the victory.

Elsewhere on the Hauraki Gulf, America True, the San Francisco-based entry with a mixed, male-female crew, easily beat Hawaiian-based Abracadabra by 1 minute 35 seconds and Nippon defeated Spain by 1:19.

Nippon has not lost a race since shifting to a new boat. Idaten is slimmer than its predecessor and skipper Peter Gilmour is pleased with its performance. "At this point, we're probably in reasonably good shape to get through to the main part of the regatta," he said, referring to January's semifinals.

And America True, the only team in the top four that brought just one boat to the regatta, continued its unexpected march to the semifinals under skipper John Cutler. True has won three of four races in the final round robin, including an impressive 20-second victory over AmericaOne on Sunday, and Monday handed faltering Abracadabra its fourth straight defeat.

The big danger for America True is a breakdown like the one that befell Stars & Stripes. With no backup boat to turn to, hull failure can be truly catastrophic.

Why do the Cup boats keep breaking? With all the millions that go into design, engineering and construction, you'd think they'd be able to handle the sort of lively sailing conditions amateur Chesapeake Bay sailors relish.

But the stakes are high and corners are cut, particularly when every ounce saved in the weight of the eggshell hull structure can be added to the 35,000-pound ballast bulbs at the bottom of the keel that keep the boats upright and powered up.

How light is too light? The late America's Cup yacht designer Ben Lexcen maintained that it was a fine line and was impossible to calculate. "If it breaks, it's too light," he used to say. "If it doesn't, it's too heavy."