(The following is a excerpt from the article, Keels Take Flight, by Barbara Lloyd, in the Nautical Quarterly, Winter 1986. I have replaced the photos in the original article with a number from my own collection at the right.)
It became apparent in 1983 that the job of shaping an America’s Cup 12-Meter was no longer the sole province of the yacht designer. High technology had become a factor that many thought, if ignored, might reduce the chances for innovation. Arvel Gentry, manager of the Aerodynamics Computing Group at the Boeing Company in Seattle, is a veteran of several America’s Cup campaigns.
Unlike most other aerospace scientists who are new to the sailing game, his experience goes back to 1968-69. He started sailing in the 1960s, and soon began producing magazine articles related to the aerodynamics of the sport – including sail and mast design. He designed the original mast on Courageous, in 1974, and his designs have been used on subsequent 12-Meters, such as Freedom, Magic and Liberty. A friendship that began in 1975 with yacht designer Johan Valentijn has brought him into the thick of the 1986-87 competition as a consultant for Valentijn, and the Eagle syndicate.
The use of winglet keels means that you’re involved in a design process for which naval architects don’t have the design tools,” says Gentry. “The tools are here; it’s just that the tools are available to different people, and they vary quite a bit.”
Gentry, whose involvement is on a voluntary basis, plays this game with a freer hand than many of the other technomasters in search of the 12-Meter dream. He works on his own and calls his own shots. But he is quick to point out that his work is as a consultant. The final decisions are up to the designer who uses information from high-tech consultants as he sees fit. In the case of Eagle, for example, Gentry might have made the wings thinner had it not been for the parameters that Valentijn set. It is the designer’s job to look at the boat on a broader scale and to decide on the eventual trade-offs that must be taken.
Gentry has the use of Boeing’s computers; but the time comes through his affiliation with the Flight Research Institute, a non-profit group dedicated to pursuing new ideas in aerospace. After the 1983 Cup races, he was approached by Dennis Conner’s Sail America syndicate, by David Pedrick, who ultimately went to work for Conner, and by Valentijn.
“When I saw the scope of Dennis’ plan, I decided to work with Johan,” says Gentry. “I thought that I could contribute more in working with Johan, who is basically responsible for all technical aspects of Eagle, than I would working through committees.” Fully aware of the hundreds of hours required in such a project, Gentry wanted to be able to spend more time at home with his family rather than spending long evenings and weekends at the office working with the Boeing computers. And so a prerequisite of his arrangement with Valentijn was that he be supplied a powerful computer to work with at home.
He got his wish: a VAXStation I, produced by the Digital Equipment Corporation, allowed him to generate winged-keel shapes mathematically through a surface geometry program. He then sent that information to the mighty Cray X-MP at Boeing, where a computer program calculated the water flow around the hull and keel. Gentry used these same techniques in supporting the design of Liberty in 1983. And they are the same computer tools that were applied in 1983 when Joop Slooff made extensive aerodynamic calculations for the Australia II effort.
In aerodynamics lingo, these programs are known as Computational Fluid Dynamics (CFD) codes. They play an important role in aircraft design, and now they contribute to sailboat design for nearly every America’s Cup syndicate. These analysts’ programs cost millions of dollars to develop, and they require supercomputers such as the Cray for their hardware needs.
The programs generate vast amounts of data, including detailed analysis of pressures on the hull and keel surfaces, flow speeds and direction of the water all around, distributions, and total lift. To understand all of it, Gentry produced elaborate color-graphic plots using the additional horsepower of a DEC VAX-780 at Boeing. By analyzing the pressure pictures for runs at various changes in heel and leeway, he was able to understand what changes in shape would be required to improve each keel design. One-third scale computer-generated lines drawings for some of these designs were furnished to Valentijn for towing-tank model construction.
Valentijn and Gentry complement one another. As the naval architect, Valentijn supplied the aerodynamicist with basic figures with which to work: the future keel’s weight, draft, span and lifting area. Gentry wondered why Valentijn had been so adamant about not exceeding a certain wing span. Later, he surmised that it was because the designer had already ordered the trailer. When the finished keel sat in its trailer bed, there was less than a half-inch to spare on either side. Valentijn is amused by Gentry’s conclusion; he insists that he had calculated maximum wingspan based on what he knew about Australia II; the fact that it ultimately fit so well on the trailer delighted him.
In the end, Gentry supplied Valentijn with a set of full-scale keel drawings on Mylar. They were computer-generated drawings that included the various station cuts, waterline cuts and buttline cuts that define a three-dimensional object. They are like a tailor’s pattern, but the end result is a keel mounted on a full-scale 12-Meter that weighs somewhere between 55,000 and 57,000 pounds.
Gentry looks at the design process for 1986 with a certain irony. Five years ago, he and other scientists at Boeing had been examining some of the same concepts that are sending designers scurrying to their towing tanks this time around. In a classic case of an idea before its time, the plans never got further than the discussion stage. Johan Valentijn designed two boats for Dennis Conner in 1983: Magic and Liberty.
In the earliest days of the program, Conner and his syndicate backer, Fritz Jewett, asked Gentry to give some thought to keel design. Gentry says that he and a group at Boeing talked about keels with winglets, double keels, rounded wings, tandem keels and side-by-side keels. But in each case they discarded these ideas as too outlandish to pass a restriction in the International 12-Meter Rule that forbids “peculiarities” in design. “In our innocence we assumed that was the rule we had to go by,” says Gentry. “We all studied the rule very carefully. I don’t remember passing these things at the time to Johan or Dennis. Early in 1983, when Johan said he’d heard that Australia II had wings, my reaction was ‘Oh my God, no!’”
The computer calculations that eventually were applied to Magic and Liberty were the same variety that Gentry has applied to Eagle. The only difference is that in 1983 there were no pressure plots. The computer power was there, but instead of being directed toward winged appendages, it went into streamlining conventional shapes. By the time Australia II’s secret weapon was out of the bag, it was too late to do something about it. The Liberty group tried wings on the 12-Meter Freedom late that summer, but it was a frivolous attempt to appease syndicate members. Gentry says that to do it right would have taken extensive analysis and tank-testing.
