Claus Polap, 37, begins his work day in the late afternoon, when the boats have been tied up in the docks of the Real Club Náutico in Valencia, Spain. The sails have been brought down and the crews are back on land. For everyone else the work day is pretty much over.

His laptop tucked under his arm, the slightly-built engineer, not exactly the ruddy seaman type, climbs onto one of the two yachts piloted by the BMW Oracle team. He kneels against the ship's side and starts up his computer. The program hums into operation, and within a few minutes every conceivable physical detail of the team's last training run has been downloaded onto the hard drive.

Every yacht is equipped with about a hundred sensors that constantly measure the forces that pull, rub and press against the ship, from the tip of the mast to the keel, from the bow to the stern. Satisfied with the data, Claus Polap snaps his laptop shut and leaves the ship to analyze the data and transmit it to the design office in Seattle. He does the same thing almost every day.

Without Polap's delivery of data from Spain, the American team's yacht builders would be in a tough spot. They're the ones who are developing the two new boats which the BMW Oracle team will be sailing in the America's Cup off the coast of Valencia. One will be used in the regatta and the other as a backup. The data collected on the boats from the last race will help develop a hull that will be simultaneously lighter and more stable than ever -- making the new yacht faster than its predecessors.

Although the race for the most sought-after trophy in the sailing world takes place only about every four years, the battle for victory in 2007 was already underway in the spring of 2003, shortly after the final match race off the coast of Auckland, New Zealand. Since then, the designers and engineers have been fine-tuning their newest creations. Top teams like Switzerland's defending champion, Alinghi, and challenger BMW Oracle, are working with budgets worth hundreds of millions of euros and approaching the project with a level of professionalism that, according to the trade publication Yacht, "is practically on par with that of Formula 1 racing."

America's Cup vessels are the queens of the water when it comes to wind-propelled water craft. With their pointed, narrow hulls, masts jutting high into the sky and small front and large main sails, they're reminiscent of the classic child's drawing of a sailboat. But the yachts in the America's Cup Class (IACC) are as delicate as they are graceful. Their enormous sail surfaces are in fact too large, subjecting the mast to loads of up to 50 tons.

The torpedo-shaped keel bomb underneath the thin keel fin that makes up almost 20 of a boat's 24 tons of total weight ensures that the yacht leans only slightly to the side. If it dips too deeply into the water, friction will slow down the boat, causing it to drift and the sails to slacken in the wind. A yacht builder's biggest challenge is to design the structure of the hull to withstand tremendous forces. The designers, says Polap, take things "right up to the limit," adding that "sailors could easily destroy their boats" by maneuvering all too abruptly.

And it's happened before: In the 2003 finals, the defending champion New Zealand team disgraced itself when their boat's mast, which was too weakly designed, collapsed onto the team, along with the sails and tackle. The "OneAustralia" met an even worse fate when it broke in half and sank within two minutes. At the next America's Cup, the "Young America" almost suffered the same fate when it snapped in the middle, but at least the boat remained in one piece.

Boat architects must develop a hull that's as rigid as possible, so that wind energy is converted into propulsion and not wasted. That's why yachts nowadays are made almost entirely of carbon, the miracle material used in both automobile and boat racing. Mats of woven carbon fibers are dipped in resin and hardened in a vacuum and at oven-like temperatures, making extremely light and expensive components that are as malleable as they are resilient.

Because this black material has not been used in shipbuilding for very long, Munich-based BMW has taken on the task of calculating the structure of the BMW Oracle's body and designing it for lightweight construction. "How many layers of carbon fiber do we need at which points? Where do we need more, and where less? How should the fibers be oriented? These are the kinds of questions we answer," says Raymond Freymann, 53, director of BMW Forschung und Technik GmbH (BMW Research and Technology, Inc.). The sailing team's experienced designers specify the shape of the hull, says Freymann, "but we add life to the hull."

In addition to metrology specialist Polap, Freymann has assigned four other BMW engineers to the project and sent them to the design center in Seattle. It was an extremely sought-after assignment at BMW, where engineers were attracted by the challenge of "taking things to the limit. That's not something you can do with a mass-production automobile project, where the goal is to design a vehicle that will last a few hundred thousand kilometers and not cause any problems."

Freymann himself spent years working in the aviation and space industry, where he helped develop rockets, airplanes and helicopters, before moving on to automobiles. Freymann, an honorary professor at Munich's Technical University, explains that a sailing yacht's movement is "highly complex, even more complicated than helicopter flight," and not just because a boat moves in two elements at the same time, water and air, but also because it encounters wave motion, creating a bow wave as its hull dips in and out of the water. In addition, wind is slowed down by friction on the ocean surface. "It's all highly variable," says Freymann.

To at least somewhat reduce the chaos of natural forces, the management of the America's Cup decided to hold the 2007 competition in a relatively predictable environment. Crews will encounter clear thermal conditions off the coast of Valencia. The sun heats the air more quickly over the Spanish land mass than over the water, and as the day progresses the heated air rises upward, pulling up cooler ocean air in its wake. This produces an onshore wind by midday, which gradually increases in speed.

Valencia was selected as the next site for the America's Cup because of experiences in 2003, when organizers were constantly having to reschedule races because of unpredictable wind conditions in the Hauraki Gulf off the coast of Auckland, which is surrounded by a maze of islands and islets over which breezes coming from various directions collide. "In the morning, we couldn't predict what the wind direction would be in the afternoon," says Rolf Vrolijk, 58, designer of the victorious "Alinghi" as well as all types of regatta craft for the past 30 years.

For the Dutch team, the first important phase of preparation began in November 2003, when it was decided that Valencia would host the next Cup. The team's meteorologists gathered historical information about the sun, precipitation, wind speeds, wind direction and barometric pressure, and constructed a network of measuring stations, because public institutions normally observe only the more general weather situation, which only provides broad information about the area in which each three-mile course is located.

Wind and weather profiles were developed on the computer using what Vrolijk calls the "enormous pile of data." Probability programs, like the ones mathematicians use to predict stock prices, helped engineers and sailors analyze how conditions develop. Then Vrolijk tested more than a hundred virtual designs using the Race Modeling Program, which he sees as "one of the most important design tools," adding that "our selection of which boats are good or bad is done entirely on the computer." Only about 20 designs survive this test series. The process saves time and money, and already came in handy in 2003.

By now, the road from concept to finished sailboat is a systematized process that takes years. Designers have long since given up on the idea that designing a boat can be the result of an overnight stroke of genius. Indeed, the rules allow for too little technical leeway to leave anything to chance. The Cup's tightly defined size requirements -- boats must be between 24 and 26 meters long and 3.5 and 4 meters wide -- are designed to produce balanced and exciting races. To the untrained eye, the only way to tell the boats in the Cup apart is by the various sponsor logos.

And because two boats will eventually compete against one another in the so-called match race, it's very important that the yachts have the right material for a duel. They must be agile and capable of accelerating quickly, even when there is little wind -- to surprise the opponent and force him into defensive mode. Designers are constantly searching for the tiniest advantages. 1:3 scale models are pulled through 300-meter pools, up to 200 times per model, quickly and slowly and in all possible positions. Oversized keel bombs are suspended in wind tunnels in which a fan produces air speeds of up to 200 kilometers per hour (about 124 mph), simulating a water speed of about 11 knots (about 20 kilometers per hour, or 12 mph).

Even old boats are used for many years for testing purposes. During test runs, they sail in parallel to one another, one equipped with a new feature and the other without the feature. For engineers, this kind of test is even worthwhile if the modified boat outruns the reference craft by as little as a foot per nautical mile. "The difference is often so minimal that you can't see it with your bare eye," says Vrolijk, "but it's there, and it counts."

The Alinghi team's triumph in 2003 is a prime example of how seemingly minor modifications can determine the outcome of the race. Instead of using a thick steel cable -- known as a "want" in sailing jargon -- to hold up the mast on both sides, Vrolijk had two thinner cables made. The thinner version was just as effective at withstanding up to 15 tons of tensile force, but offered less wind resistance. The innovation apparently reduced the boat's sailing time by half a second per minute. Was it negligible? The crew didn't think so -- after all, it helped them win the race.