The challenges meteorologists face in the 33rd America's Cup
Jon Bilger and Jack Katzfey, Alinghi's meteorologists, talked this afternoon about the challenges they face in their every day task of giving the sailing team an accurate forecast of the winds in Valencia. Although, the 32nd and the 33rd America's Cups were held on the same waters, there are major differences.
Differences between the 32nd and 33rd America's Cups
It doesn't come as a surprise that one of the most important differences between the previous and this edition of the America's Cup is the season it takes place. While in the 32nd America's Cup match, Alinghi defended the trophy in July, in this edition the Swiss are racing in February. The weather in Valencia is much more unstable and thus unpredictable in winter, making the meteorologist's work tougher. In addition, the race course is 44 times bigger, leaping from a mere 9 square nautical miles to 400 square nautical miles.
The radical differences between the yachts used in the two races also result in a fundamental change in the approach to wind prediction. The giant multihulls reach speeds equal to three times the wind of speed. Just a couple of knots in wind speed make a significant difference in boat speed, thus making accurate prediction of wind speed a much more critical factor than wind direction. According to Bilger, when Alinghi 5 sails at 6-7 knots of wind, a mere knot of wind pressure is roughly equal to a shift of 20 degrees!!
Tacking in these yachts takes a crucial amount of time and as a result, the meteorologist's strategy is based on reducing the number of tacks and on the yachts sailing on the edges of the course.
Finally, a direct result of the speeds these yachts reach is the limited visibility ahead sailors have. A sailor on the deck of a conventional ACC yacht has a visibility of approximately 10 minutes ahead of him, which can be increased to 16 minutes from the top of the mast. On the other hand, a sailor onboard Alinghi 5 has an average visibility of just 3 minutes. Since nobody goes up the mast, sailors on Alinghi 5 are, according to Bilger, almost "blind", relying heavily on accurate weather prediction.
Alinghi has a total of 9 weather boats as well as a number of meteorological stations. Most of them are placed on strategic locations of the Valencia coast but there is a number of them offshore, even as far as the island of Ibiza.
The great novelty this time are the two "microlight" airplanes. They are very light and small powered hang gliders, equipped with wind measurement devices. They fly up to 100 meters high and reach speeds of 40 knots. According to Bilger, their measurements are very accurate with the additional advantage of being much cheaper to acquire and operate than a traditional speed boat.
Finally, Alinghi has a wind profiler at the edge of the port. It is a radar that measures wind speed and direction up to 1,000 meters high, every 10 meters. Wit the boats having masts of 60 or even 70 meters it is very important to be able to measure wind speed at those heights since they are different from those at 10 meters.
The weather team will make a forecast early in the morning in order for the shore crew to set the boat's configuration. The weather boats and airplanes will then be sent out according to that forecast. The teams makes two more forecasts, one starting 6 hours before the race that will decide the sails to be used and another one, a strategic call, from 3 hours before the race, up to 15 minutes before the gun.
In the case of a race start at 10am the weather boats and airplanes will be sent out at 6:45am, sail choice will be made at 8:30am while at 8:45am the weather team will give his final advice for the favored side of the race course. The very last weather call to Alinghi 5 is made 8 minutes before the start. This will give the crew 3 minutes to store all communication equipment into a waterproof case and throw it out of the yacht.