Science / Medicine : Technology Sailing Into Forefront of Yacht Racing
As if to prove that the America’s Cup trophy is indeed awarded to the winner of a boat race, and not to a team of lawyers for their prowess in court, contestants in this year’s America’s Cup will soon take to the waters off San Diego to sail against each other. But the legal tacks and jibes of the last year have made this a match race unrivaled by any in the Cup’s 137-year history.
A judge’s literal interpretation of the original rules has unbound boat designers from decades of tradition and transformed this year’s race into a no-holds-barred contest. As a match of widely disparate boat designs, constrained by little more than a maximum waterline length and the desire for speed, the race may not be an even test of yachting skill, but it will offer a showcase for many of the innovations that are endowing yachts with strange outlines and unprecedented speed.
The America’s Cup hopefuls will show off leading-edge technology and engineering in the mono-hulled New Zealand and the double-hulled Stars and Stripes. After a long court battle over the rules, the Mercury Bay Boat Club’s New Zealand and the San Diego Yacht Club’s Stars and Stripes will race for the Cup starting Wednesday.
The key to making a fast sailboat is the same as making a fast anything: Maximize thrust and reduce drag. For sailboats, maximizing thrust means increasing the size and efficiency of the sail, which acts like an airplane wing to give the boat “lift.” Most of the drag on a boat in light winds, typical off San Diego, comes from the water, so reducing drag requires reducing weight. This makes the boat sit higher in the water.
If this were all the designers had to worry about, the answer would be obvious: Make a very small boat with a huge sail. Unfortunately, such a boat tips easily, so designers must strive to craft a boat that balances an equation involving sail size, weight and stability.
The New Zealanders picked the traditional answer by making a boat of enormous size. The New Zealand has a 150-foot mast and is 90 feet long at waterline, the maximum length allowed by America’s Cup rules. But its construction is highly untraditional. With new materials and modern design, the builders have attempted to get he maximum sail area without adding much weight or losing stability.
The savings in weight come from using new types of carbon fiber composites to build the boat.
When weight is lost, stability must be acquired in other ways. New Zealand’s designers did this by making the hull flare out above the waterline, giving the gargantuan boat the look of an aircraft carrier with a mast and bowsprit.
Designers of Stars and Stripes catamaran have opted to emphasize light weight and stability rather than size. Stars and Stripes’ most striking feature is that its mainsail does not look like a sail at all, but rather a solid, vertical wing. Instead of a fabric sail and a mast, the “wing sail” is a two-piece Kevlar- and Mylar-covered foil that gives the boat more lift and less wind resistance than a conventional sail, said wing-sail co-designer David Hubbard of Pitney-Bowes in Norwalk, Conn.
“The wing shape is aerodynamically cleaner and gives more lift per square foot of sail,” Hubbard said. One reason the wing sail provides more lift is that it is tall and narrow from front to back. Since most lift occurs near the leading edge of a wing, this maximizes lift for a given sail size.
To ensure maximum lift, the sail is actually constructed out of two foils, one in back of the other. The flow of air through a slot between the foils keeps the wind pinned to the surface of the rear foil when it might otherwise break away and eddy on a single foil.
Many observers expect the catamaran to sail away with the race, but a few caution that the outcome is not foreordained. In light wind and choppy seas the catamaran’s two hulls will bounce the boat around, slowing it considerably, notes Stars and Stripes Design Program Manager John Marshall.
New Zealand’s size could also offer an advantage. A common sailing tactic is to “cover” the competition by putting your boat upwind of them to block the “air,” or wind. If Stars and Stripes is unlucky enough to be covered by the nearly half-acre of sail on New Zealand, “we’ll have to reach for our oxygen masks,” Marshall said.