Dirk Kramers on Nova
America’s Cup racing rang enough bells to become part of the Nova program, Making Things Fast, that runs Wednesday evening, October 16, on PBS. Dirk Kramers, engineer and design executive for Oracle Team USA, is the go-to guy for David Pogue as Nova explores the techniques and implications of moving humans and machines ever faster. Pogue asks, “Is it possible to go too fast? Have we hit a point where innovation outpaces our ability to keep up?”
Recognizing an opportunity for a conversation with Dirk, I interrupted his packing up post-America’s Cup 34—goodbye, Tiburon CA, hello Newport RI and home—to talk foils and wings and boats and how dramatically the America’s Cup catamarans made leeway. “From a helicopter,” Kramers said, “you’re really struck by it.”
And leeway factors into the entire “flying” equation.
About a million years ago, Emirates Team New Zealand set out testing standard C-shaped foils on Morrelli & Melvin-designed 33-foot catamarans with elevators added to the rudders. The result was a lifting force equal to about 50 percent of displacement, but M&M’s Pete Melvin (also a designer of the AC72 rule and of the Kiwi AC72) pointed out in a separate conversation that, “C-foils are locked in to a narrow range of lift.”
L-foils came next, with the discovery that they would lift dramatically and produce a burst of speed (Melvin again: “We asked ourselves, how can we bottle this?”) but with that success you had less of the daggerboard shaft in the water, and less resistance to leeway, and with increased leeway came a shift in the flow over the horizontal foil that brought the whole shebang crashing DOWN.
Next from the experiments of the Kiwi designers came the V-foil, with the lifting foil angled up. If you want to sound like an engineer, throw in the word dihedral, the angle between two intersecting planes. Employing a curved board, you can set a working/sailing angle up from horizontal, though when it’s lifted the eye sees it as horizontal to the surface. With a straight board, you can achieve the same goal with a pronounced dihedral. If you remember the images of AC45s flying on San Francisco Bay in the summer of 2012, you know where Oracle was able to come in.
Kramers recalled, “With that configuration, leeway causes moderate loss of lift instead of complete loss of lift.” In this environment, that translates to stability. “All of us on all the teams spent a lot of time trying to hit the ideal compromise,” Kramers said. “The more extreme the dihedral, the more stable the ride, but the downside is more drag. The better your control system, the more you can afford to lower the drag. Angles, twists, radii—it’s a search for a combination.” Speaking of better control systems, and historic comebacks, note the dihedral difference in this final-day shot by Daniel Forster compared to the crane shot from earlier in the season.
The concepts aren’t new, but the application of intense R&D? You betcha.
“At 50 knots apparent, you stumble upon the side effects,” Kramers said. “You want a clean undercarriage, and even bodies on deck become a big deal in terms of windage.
“Another thing—for the Cup we were allowed three sails up front, but it wasn’t like ordinary sailing where you’re looking to carry the biggest sail possible. It was a game of how little sail you could get away with.”
OK, Dirk, I know you want to get out the door, but what about this whole pitch-control system on the 2013 boats? Dihedral foils on the bottoms of canting, raking, elevating daggerboards with fixed winglets to push against. What do we get if the next design rule, for whatever size boat, erases the prohibition on trimmable winglets?
“I really don’t know what’s going to happen, and the solution we ended up with was really rather elegant. But you would never design an airplane that way. Give us trimmable winglets, and the boats will go faster, and we’ll reduce the risk of crashes.”
Nova: Click Making Stuff Faster to find your local listing.
Are there physical limits to how fast humans can go? David Pogue wants to find out how much we can tweak physiology and engineering to move humans and machines even faster. He investigates everything from lightning-fast electric muscle cars to ultra-sleek sailboats to ultra-fast cameras and quantum teleportation. But faster is also about efficiency and the science of optimization: getting things done in less time. From the floor of the New York Stock Exchange to UPS headquarters and inside a packed 737, Pogue’s quest for ultimate speed limits takes him to unexpected places where he comes face-to-face with the final frontiers of speed. NOVA also explores important questions: Is it possible to go too fast? Have we hit a point where innovation outpaces our ability to keep up?