From the Oracle site, Team Photographer : Guilain GRENIER
The AC45 wingsail catamaran has been dubbed the “Little sister with attitude” to the
AC72, the featured catamaran for the 34th America’s Cup in 2013.
The prototype AC45 hit the water in Auckland, New Zealand, on Jan. 17, 2011, making
it the first series-built one-design class to be featured in the storied history of America’s
The AC45 came about as a means to fast-track teams’ understanding of wingsail
catamaran sailing. The craft was conceived by ORACLE TEAM USA’s designers and
engineers on behalf of the America’s Cup community.
The catamaran was built by Core Builders Composites, ORACLE TEAM USA’s
boatbuilding affiliate in Warkworth, New Zealand. Led by Tim Smyth and Mark Turner,
precise tooling and techniques were used to create molds that will produce identical
”Everything with the AC45 has turned out better than we hoped. It’s living up to
expectations for what we were shooting for: good class racing in a high-performance
catamaran,” said Ian Burns of the ORACLE TEAM USA performance team.
The brief for the new design included many features: It had to be easy to assemble and
disassemble to accommodate the active racing schedule and also to fit inside a 40-foot
container for shipping.
It had to be robust enough to sail through a wide wind range, from 5 to 30 knots, and
also survive in the event of collisions.
Settling on the 45-foot length came about after studies suggested it was best to solution
to avoid nose-diving tendencies, which can occur with short hull lengths and highaspect sail configurations.
The cat will fit inside a container aided by removable sterns. The aft cross beam has
been set forward to allow the removal of the final five feet of the hulls. Those sections
are bolted on a flange and the crossbeams also are bolted in place.
The hulls are built in carbon epoxy with honeycomb cores, making them extremely stiff
and light structures. The sandwich construction involves two carbon skins less than
1mm thick laminated over an ultra-light honeycomb core, with the laminates baked
under vacuum pressure in a giant oven for eight hours at 80°C.
See AC-45 flying AC-45 flying
FROM THE 1ST QUARTER IHS NEWSLETTER:
What is 72 feet long, has half a wing, 13 bodies, 26 legs but uses only 2 legs to go 50mph on 25mph of wind power? Did I mention it cost over $100,000,000? If you failed the test, don't worry. Until recently 250,000,000 other Americans probably don't know the answer. That has changed. For example:
My wife and I are ordering lunch in the Yard House, the largest downtown sport bar in the port of Seattle. We are surrounded by giant TV sets playing basketball, football, tennis, whatever. The most exciting race in sailing history starts in ten minutes and in response to our interest the waiter needs to ask the bartender, "Can we get the America's Cup?"
Team Oracle is trailing the New Zealand team 1 win to 8 and this will be the last race if the Americans lose. Patricia and I and one other couple are watching, jumping, and cheering. The football fans are becoming irritated about the disturbance.
Oracle wins the race. Over the following days they continue to be unbeatable for the final 7 races. In one of the greatest come-backs ever, the Americans have overcome impossible odds to retain the Cup. How many spectators joined in, and how did the Oracle team pull it off?
During the regatta, 870,000 spectators paid at least $20 admission to be in the official viewing locations and probably a million more viewed from informal venues. Perhaps there were 5,000,000 views on live U.S. television, and over 3,000,000 Youtube viewers have since watched the TV reruns as you may do by searching forAmerica’s Cup at http://www.youtube.com). Additionally, live TV coverage was in 170 other countries. In New Zealand, a country of 4.4 million people, there were 927,000 viewers. No word on the 31 million sheep.
So how did Oracle come back so dramatically?
The race can be broken down into 3 phases (remember, because of a penalty in the AC-35 races, the two earliest wins were not counted).
Phase one, losing. Race numbers zero to 5. Oracle, won 1, lost 4. Score: zero to 4.
Phase two, improving: Races 6 to 11. Oracle won 2, lost 4. Score: 1 to 8.
Phase three, coming back: Races 12 through 19. Oracle looses none, wins 8 races. Final score: 9 to 8.
To enter the improving phase, after race number 5, Oracle exercised their postponement option and delayed one race followed by a racing lay day. This gave the team a chance to have all-hands meeting like NASA’s crisis meeting when correcting the Apollo 13 near disaster. Oracle management, engineers, and crew met to brainstorm. Several changes were made:
The center spine and bow sprint were shortened for better upwind performance.
The wing controls were modified to allow more twist high up and more curve down low. There is a “tab” on the trailing edge of the leading wing element that is designed to control the air flow between the two wing elements. The tab was adjusted to allow the slot in the wing to be open. The result was a shifting of the center of effort aft. That improved the balance of the helm, which in turn, improved upwind performance.
The hydrofoils needed some attention. All were designed for sub-cavitating conditions. But cavitation was being experienced at the intersections of the rear struts and foils as evidenced by the necessity of frequent repainting. The solution was to add torpedo-shaped fairings to the junctions. These were tuned a little on each run.
There was also cavitation at the junctions of the daggerboards and the struts. Because of the curved intersections, this was more difficult to treat. One could speculate that modifying the profile of the foil at the curve might help, but it is not known if this or anything else was tried.
It was discovered that when the Oracle boat was heeled, the V shape of the foil caused it perform like a surface piercing foil and therefore contributed to height setting stability. Also the leeward vs. vertical lift forces could be manipulated to control pitch and directional stability.
The upwind VMG, Velocity Made Good, was improved. This is the speed that the craft approaches the next mark. On the upwind legs it was discovered that by sailing slightly farther off the wind, full hydrofoiling is possible. Thereby much greater speeds are obtained. Obviously they were sailing farther off course, but the greater speeds more than made up for the increased distance. In this way, the VMG was improved.
It was discovered that the tacking techniques for monohulls and catamarans were not suitable for hydrofoils. Traditional tacking, when used on the AC72, put both hulls and all foils in the water for a relatively long time as the bow passed through the wind. The velocity during the tack was in the range of 12 to 14 knots.
New Zealand first developed and Oracle learned to do “Fast Hydrofoil Assisted Tacking”. As the boat points upwind the windward foils descend onto the water. As the tack continues, when opposite foil becomes the windward foil its hydrofoil’s AOA is sharply increased by hydraulically rotating the daggerboard on its pivot. This increases lift and the hull is quickly raised above the surface and windward hull drag is eliminated. The velocity during the tack increased to 12 – 18 knots. An excellent video with details on this technique can be viewed at: Link
A new tactician replaced the original, but in defense of the original, nothing increases wins more than having a faster boat.
Other proposed theories looked for the one big change that made the difference, like the one published by the English Seahorse Magazine. Here’s a quote from their December issue: "The new pitch system…is in principle a position system that uses mechanical feedback." Simply explained, two designated crew members had two buttons each. One button increased the AOA, Angle Of Attack, one button decreased the AOA. The hydraulic power was provided by the human “grinders” and a hydraulic feedback system was developed to compensate for changes in hydraulic pressure and for variable shared demand. The system allowed the pitch and height to be controlled, thus enabling extended flight. This would be a good explanation for the later winning streak, however the system was in place prior to the first race. What improved was team Oracle’s technique in using the existing system, especially upwind where the boat was more unstable and difficult to fly.
To learn more about Oracle's hydraulic control of the cant, lift, and pitch of the daggerboard hydrofoil units, read "Americas Cup 34: The Power of Oil". The Power of Oil
So what was the big fuss about rule bending, and why were the teams so contentious about changes during the race? It relates back to the original rule modifications introduced by the First Challenger of Record, Club Nautico di Roma. By mutual consent, to keep the costs down, they restricted the design of the foil control system to keep them from being true, freely flying hydrofoils. The idea was that there would be two conditions of fast flight. First, a skimming mode were the foils created lift with low drag. But to maintain stability the hulls would remain on the surface, but barely touching. Second, there would be periods of pitch-unstable flight lasting for a limited number of boat lengths. For more:Link
One of these handicapping rules dictated that the rear foil’s AOA can not be adjusted after 5 minute prior to the race. Unfortunately, this aggravated a safety problem. Pitch poling plagued the boats, and they would have would have been safer if the rear foil’s AOA could be quickly reduced to prevent pitching forward and burying the bow.
Likewise, the front foils could not use any existing, safer, design to create a stability and controllability in pitch and height.
So invention was necessary and this is where the New Zealanders gained an advantage. Long before the San Francisco regatta, working with the SL33 catamaran, they did extensive experimentation with foils and daggerboards. Whereas the number of experimental boards for the AC72 is limited to ten at the commencement of the race and each set costs $400,000 or more, the SL33 foils and daggerboards cost $5,000 to $8,000 and the rules do not limit the number of permutations.
Beautiful in its simplicity, the answer was to curve the daggerboards and transform the lower parts into hydrofoils. With the boards retracted or partially extended, the main foil is horizontal. With the boards fully deployed the junction of the foil and the board changes from an ‘L’ shape to a ‘V’ shape. This not only increases the horizontal wetted area, increasing lift, but it also creates a surface piercing configuration which is a time tested design for height setting hydrofoils. For examples, see the Canadian Navy ship, Bras d’Or or the experimental Carl XCH-4, page 4 of Hydrofoils: Design, Build, Fly.
Both AC72 boats arrived in San Francisco with ‘L’ foils and curved daggerboards.
Insert Illustration HERE.
Is it possible that the Club Nautico di Roma went the wrong way with the rules? Perhaps for safety, stability, and efficiency the front foil height finding mechanism should be automated. These systems can react more quickly and more subtly than humans. The cost of adapting one of the many systems in current use might be less than that of the custom designed mechanical/hydraulic feedback positioning system.
According to scuttlebutt, some designers like the idea of having flaps on the daggerboard foils and a variable angle of incidence on the rear foil. I support this idea.
Perhaps four years from now in the venue Larry Ellison chooses for the next Americas Cup, the rules will provide for faster, equally exciting, but even safer racing.
Author, Hydrofoils: Design, Build, Fly