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America's Cup: Bang! New video of Foil Arm Destruction Testing

by Richard Gladwell, Sail-World.com/nz 22 May 15:40 BST 23 May 2019
Final destruction test- AC75 foil arms - Persico Marine - May 2019. © America's Cup Media

A video has been released by America's Cup which shows the two destruction tests of the carbon foil arms for the AC75.

The tests were undertaken at Persico Marine, who will build Italian America's Cup Challenger of Record Luna Rossa's two AC75s.

The first test of the carbon foil arm failed earlier than expected in September 2018, triggering rumours about the state of the project in which Emirates Team New Zealand was charged with developing the foil arm mechanism, while Luna Rossa was responsible for the design and build of the carbon arm. Both the foil arm and the raising mechanism are one design parts and are supplied to the other teams as standard equipment.

In the first round of testing the foil got through to the second phase of the test before breaking with a sound like an exploding bomb.

"At 88% of the maximum test load in the first test, we heard some noise from the arm," recalled Luna Rossa's Davide Tagliapietra. "We got a warning from the acoustic emission device."

"We decided to skip that test and pass onto the next one, because there were areas that we could better understand in the next test plan."

During the second phase of the first test the board failed unexpectedly with a noise like a bomb exploding as the test rig crumpled.

"We have no confidence to carry on with this architecture," said Tagliapietra - in the biggest understatement so far in the 36th America's Cup.

The competing teams then decided to collaborate, and Auckland based composite design team Pure Design and Engineering team was also included in the new project team.

Fast forward eight months to mid-May 2019, and the combined engineering group reassembles at Persico.

"This type of boat has never been done before," said ETNZ designer Guillaume Verdier - recognised as the world's leading high performance yacht designer.

"This is the first time we have introduced this new kind of architecture. We want to make sure it works," the French designer added.

"It's not very often that you get the opportunity to test something to this level, and have this amount of information available," explained Andrew Corkery of Pure Design and Engineering.

"But there is also the uncertainty that you are putting something into the test rig that has never been tested before. You never know what can go wrong," he added.

Verdier says the design team are treading a fine line between weight and strength in the carbon foil.

"It has to be light to be able to take off on the foils in light winds. We can't afford to produce something that is too heavy and will not allow us to foil as soon as possible," he added.

Like a countdown for a rocket launch, the load cylinder is called.

"Three tonnes, four tonnes," starts the load call, as the engineers watch various screens that show the S-shaped arm and the loads that are being experienced at various points of the test foil.

The new foil design passed all of the preliminary tests before going into the final test.

"This last test is one way, there is no way back. Breaking this arm is going beyond the usual engineering screening that we normally do on components," explains Alessandro Franceschetti, Head of Structures for Luna Rossa.

"We are in a zone where we will be able to understand the behavior of these structures over extreme limits up to the very end," he adds.

The load cylinder can pull 35 tonnes. "There is no way back," says Franceschetti.

The test goes well with 180% of working load being called as the load cell reads over 27.3 tonnes before the foil arm explodes in a shower of carbon beyond the 27.5 tonne mark to the applause of the relieved engineers.

"We heard some cracking on the way up but we got to over 2.1 times the safe working load, and that was the expected minimum, says Franceschetti.

"We're good to go," he smiles. "We've got an arm, we look forward to seeing the AC75's on the water, now."

Second version of the video released May 23 by America's Cup Youtube channel

Uncut version - 7m30secs duration

For an earlier report on the destruction testing, including a description of the test cases and their purpose click here

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