The America's Cup: nerves, skill and a lot of computers
The teams used to test their boat designs in wind tunnels and water tanks, but they now do most of it with computers
Image credit: Emirates Team New Zealand
This year's America's Cup will be remembered for Oracle Team USA's jaw-dropping comeback against Emirates New Zealand, but it should also be remembered for the huge role computers have come to play in the competition.
The teams raced 72-foot twin-hull catamarans that are so fragile and finely tuned that they have more in common with Formula One race cars than traditional sailboats, and they made this competition on the blustery San Francisco Bay both exciting to watch and dangerous for those taking part.
Long before the boats hit the water, the teams used powerful computers to model small changes in their design and extract maximum performance. It's hard to overestimate the role computer-aided design tools have come to play.
Image credit: Image credit: Emirates Team New Zealand
Nick Holroyd, technical director for Emirates Team New Zealand, has been doing America's Cup races for 18 years. In that time, he said in a recent interview, New Zealand has gone from "almost 100% physical testing," where design changes were tested in wind tunnels and water tanks, to this year's competition, which was "the first where we've done basically everything using computer simulation."
In years past, he said, teams did three or four "tank sessions" a year, allowing them to test about two dozen hull designs. With high-performance computers, they can now test 300 designs in the same amount of time, and with greater precision.
This year's boat class was so sophisticated it's not surprising that computers played such a critical role. The catamarans have a towering, 131-foot wing sail made from a lightweight, carbon fiber frame, covered with plastic sheeting only six times thicker than kitchen wrap.
The sail has flaps like those on an airplane wing that are adjusted to maximize performance, and the boats are at their most spectacular when they lift clean into the air and hydrofoil at speeds approaching 50 mph, held aloft on retractable keels, or "dagger boards," that descend from the center of each hull.
In the run-up to the race, the teams make modifications to the shape of a hull or the size of a rudder and model its effect with computational fluid dynamics. They plug hydrodynamic and aerodynamic data into a velocity prediction program that shows the effect the change will have on the speed of the boat, its angle of heel and other variables.
"When you work in a physical tank, you can look at the wave patterns around a hull and you can get a really accurate drag number from the gauge, but it doesn't tell you a thing about why one model is better than another," Holroyd said.
The computer simulations reveal details like whether the drag is greater at the front or the back of a hull, aiding further optimization. As a result, the catamarans in this year's competition were 30 to 40% faster than originally envisaged for their class.
For its design work, Emirates Team New Zealand used a cluster of Dell PowerEdge C6100 servers with six-core Intel X5670 CPUs. The system had 576 cores and 1.2TB of RAM, consumed about 35 kilowatts and at the time was "the biggest system you could get in a single rack," according to Holroyd.
The team did some test runs on an HPC at Cambridge University in England to figure out the most cost-effective architecture they could use. Their two main applications are memory-constrained rather than CPU-constrained, and they found they could get away with using lower-power processors.
They chose Infiniband over Gigabit Ethernet to link the server nodes, which kept their software licensing costs lower. That's because one of the team's vendors had a "very nonlinear" pricing model, Holroyd said, "so it was cheaper to run a few jobs across a lot of cores than a lot of jobs on a few cores."
All the teams had access to high-performance computers; Oracle used its own Exadata systems to design its boat, a spokeswoman said.
The computerized modeling helped the Kiwis come up with one important breakthrough in particular. It didn't help them win the tournament, but the fact they figured it out early on in the campaign helped them move ahead with the design of their boat.
The boat design chosen for this year's Cup was not intended to be able to hydrofoil. "They thought that would make it too easy" and reduce the importance of the skill of the sailors, Ross Blackman, a business manager with Emirates Team New Zealand, said last week.
But the Kiwis were the first to figure out how to design a dagger board and rudders that allowed their boat to lift out of the water, yet stay within the class rules. It was a change that required precise calculations and "a huge amount of modeling," Holroyd said. When the 6-ton catamaran gets close to top speed, the pressure on the "suction" side of the dagger board is so low that water "boils" at the point of contact, creating vapor, he said. That causes drag and is also quite dangerous.
After New Zealand figured out how to make its boat hydrofoil, the other teams had to follow suit. By then, the Kiwis could focus more attention on other areas of their boat.
But this year's contest showed that nerves and psychology are as important as who has the best boat. At one point last week, New Zealand was leading Oracle by seven races and needed only one more for victory. Oracle Team USA won eight races in a row to pull off the biggest comeback in America's Cup history.