Capturing the Wind, and More
They take their sailing seriously in New Zealand. Last week, that country's entry in the prestigious America's Cup sailboat race streaked to a 5 race to 0 win over Italy. On Saturday, 250,000 fans filled the streets of the capital city Auckland to cheer the victorious crew.

For 150 years, teams from around the world have vied to win sailing's most famous competition. But besides racing against each other, the sailboat crews are competing against the physical forces of nature--and with increasing know-how. What are these forces and how have the designers and crews of these boats responded?

Whether you are sailing a state-of-the-art racing boat or the smallest dinghy, the main idea in sailing is to collect the force of the wind and to redirect it so you can move forward. All other factors being equal, the greater the velocity of the wind, the greater force it exerts on the sail, and the faster your boat can travel.

In an ideal situation, the wind would blow hard, and the sailboat would go full speed ahead. But there are other forces a sailor--and a boat designer--have to consider. For starters, the contact between the water and the boat's hull produces friction. This friction can become substantial because the boat's keel--which is needed for stability--extends downward several feet into the water.

The condition that results is called "drag," which slows the speed of the boat and resembles the drag caused by the tail of a kite flying in the air. (See the article "The Magic and Science of Kites.")

Water currents can speed up or slow the boat, depending on their direction. "Wave resistance" also enters the equation. The faster a boat moves, the larger the waves it creates, and the more wave resistance it encounters.

Then there's the matter of dealing with the wind, which frequently shifts. In response, the boat's crew changes the direction of the boat and the angle at which it sails with respect to the wind, while also changing the angles and shapes of the sails--all to capture the maximum amount and velocity of wind.

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New Technologies
The technology driving racing boats is moving as fast as the boats themselves. "There's always development going on," says John Reichel, the chief naval architect for Reichel-Pugh Yacht Design in San Diego.

Reichel should know, having designed boats for the last three America's Cups. He has seen a host of changes over the last decade, starting with the sails these boats use.

"Sails are really advanced now," Reichel observes. "They used to make them out of cotton. Now they're made out of mylar or kevlar panels that are super strong and super light. They're also made out of one piece to stand up to the wind forces. You don't want to deform the shape of the sail so that you lose the wind."

As for the hull and keel of the boats, lighter is proving better. A honeycomb core material covered with a carbon fiber skin makes the modern racing boat a lot like the most advanced jet planes.

And computerized programs have provided new tools to Reichel and other boat designers. "We now have computational fluid dynamics programs," he explains, "that predict wave patterns and wave resistances at different speeds." He uses that information to adjust the boat's size, shape, and weight.

• View other racing boats designed by John Reichel.
  
  
• Take an interactive video tour of an America's Cup racing boat. You'll need the free QuickTime plug-in.