From the skies to the seas: How jet design and yacht design overlap
by Claire Wrathall
When the sloop-rigged racing trimaran USA 17 won the 33rd America’s Cup for Oracle Team USA in 2010, its rigid wingsail was, and remains, the largest ever. With a height of 67.97 metres, it was more than twice the size of the wing of a Boeing 747. At least, that was the comparison often made.
Seven years later, the new AC class catamarans that competed for the Auld Mug in June 2017 had an LOA of 15 metres and a wingsail of 23.77 metres, making them the smallest multihulls yet to compete for the world’s oldest international sporting trophy. But the aircraft analogy remains apposite, because the crossover between yacht and aerodynamic technology and design is ever increasing, and the potential for both industries to benefit is big.
This time “the size of the wingsail on the Oracle boat was the same as the wing of an Airbus A320,” says Pierre-Marie Belleau, head of business development at the commercial aircraft manufacturer’s France-based HQ, which collaborated with the US team on the AC50 catamaran that defended last year’s 35th edition of the competition, eventually losing out to Emirates Team New Zealand.
It wasn’t only their dimensions that the catamaran sail and aircraft wing had in common; parts of their structure were extremely similar, too. On an aircraft “the airflow around the wing creates greater pressure on one side than the other, so creating lift,” Belleau explains. “So, just as in an airplane, the shape of the wingsail is important because it is what drives the speed of the boat.”
As is the design of the hydrodynamic foils that enable the 14.93 metre catamaran to rise out of the water and fly above it at speeds up to four times greater than the wind. “On a traditional yacht, at speeds below 20 knots, the problem is the drag of the water, so aerodynamics are not a concern,” he continues. “But when you go to 40 to 45 knots, aerodynamic drag becomes a primary factor.”
Hence the L-shaped form of the foils, which replicate the upturned tips on the wings of Airbus’s private and commercial aircraft — the Sharklets, as it has trademarked them — to improve fuel consumption and range.
Belleau and I are talking, along with Fabrice Brégier, president and CEO of Airbus, at Oracle Team USA’s HQ in Bermuda’s historic Royal Naval Dockyard, overlooking the dazzling turquoise water of the Great Sound, where up to 30 Airbus aeronautical engineers have contributed to the design of the boat over the past three years, a handful of them assigned to the project full-time.
The collaboration began in 2012 with what Brégier calls “low-level discussions”, in which “we compared notes over the technical convergence between these boats and Airbus aircraft”, concluding they had much in common.
Invert a model of an average boat and, if you imagine the keel as a tail fin, what you have is not so removed from the body of a plane.
“You can see how boats are looking closer and closer to planes.”
As with aircraft, “there is a constant fight in order to reduce weight”, says Belleau, hence the ongoing “quest” to develop lighter and stronger materials that can bring about “a step change in the continuum”.
To this end “the aeronautical industry really has pushed the use of carbon fibre. The A320 and its business jet sibling, the ACJ320, which were developed in the 1980s and 90s, were originally 100 per cent aluminium. Now they are about 60 per cent carbon fibre.”
Airbus’s newest private jet, the fully customisable ACJ350 XWB, arguably the world’s most modern VIP plane, which has a range of 10,800 nautical miles or 22 hours of flying time, is 53 per cent carbon fibre. In time this proportion is likely to approach the AC catamaran’s 72 per cent.
The other game changer has been 3D printing, which enables Airbus to produce components of much greater geometrical complexity, yet with the strength of titanium. “With complex pieces such as the foils this can save 40 per cent of the weight,” Belleau says.
Each hydrofoil, for example, weighs 79.83kg and is composed of 16,000 parts but it has to support the entire 2.4 tonne weight of the boat when it rises out of the water. It’s also much faster.
“Producing a piece for a rudder or foil with the traditional means of production might take about a month, but with 3D printing it takes two days.” This allows Airbus to be much more adventurous than it would in the development of an aircraft, where obviously passenger safety and longevity are paramount.
Laurent Chatillon is one of the Airbus engineers who moved out to Bermuda to work on the project. He believes that, in terms of innovation, yacht design is lagging “perhaps 30 or 40 years behind aviation engineering, so the potential for innovation and synergy is wide open. This is only the beginning”.
The catamarans that competed for the America’s Cup last summer were powered by the wind and the strength of the grinders (or, in Emirates Team New Zealand’s case, the “cyclors”), who produce the necessary pressure of 5,000psi to power the hydraulic systems that operate the wingsail, jib, foils and rudders.
This was equivalent to the same pounds-per-square-inch pressure as used on an ACJ350 XWB, so was in effect “transferring Airbus flight control system knowhow into an AC class cockpit”. Again, Belleau adds, “this was completely new for yacht design.”
Take, too, the new generation of pressure sensors, technology similar to that on the touchscreen of a smartphone, known as MEMS
(or micro-electromechanical systems), which can be found on the new A350-1000 and its private jet sibling, the ACJ350 XWB.
Visible as little stripes at regular intervals set along the line of the leech of the boat’s wingsail, they act as micro anemometers to measure the wind and atmospheric pressure, providing a stream of detailed data on airflow around the wingsail.
“I would not be surprised if this becomes a standard for the yachting industry in the future,” says Belleau, explaining that data capture of this kind should in time enable mapping of the winds in the Atlantic with a much greater degree of precision. “When you look at [most] weather forecasting data, it has no accuracy and doesn’t take into account all the local effects such as sea temperature.” Another potential boon for sailors and pilots.
The benefits to Oracle Team USA of this collaboration are obvious: the America’s Cup has long been as much about the technological sophistication of the boats as the skill of their crews. But given that its business is building aircraft, what was in it for Airbus?
“What I want to keep at all costs is a spirit of innovation,” replies Brégier. And this was a chance to experiment and push boundaries, “to test ideas, simulations and materials in real conditions. Some have been incorporated into the boat, others were rejected. But you can learn a lot from failure”.
As Jimmy Spithill, Oracle Team USA’s skipper, has identified: “There are a huge amount of similarities between flying and sailing. It’s all about lift and drag. A well set up boat is like a well set up plane.” Spithill has a private pilot’s license, so he should know.
Indeed, there’s synergy when it comes to piloting them. Working with Oracle Team USA presented an opportunity “to go to the limit,” he says. So when Airbus decided to market its ACJs as “the world’s most modern corporate jet family”, it wasn’t exaggerating.
First published in the October 2017 US edition of Boat International.