Cup Spy Nov 21: Kiwi capsize aftermath .. Italians unveil sensors
by Richard Gladwell Sail-World NZ 22 Nov 2022 15:16 AEDT
22 November 2022
Luna Rossa Prada Pirelli - Tow test - LEQ12 - November 21, 2022 - Cagliari © Ivo Rovira / America'sCup
What happened in the Cup - November 21, 2022:
- Luna Rossa went for a test tow in their LEQ12 with some new sensors attached to the port wing foil. They expect to be sailing in 7-10 days.
- Emirates Team New Zealand are re-evaluating their situation after severely damaging the bow of their AC40 in a training incident.
- Alinghi Red Bull Racing is back in the shed for an upgrade - not expected to emerge until the end of November.
- American Magic did not sail in Pensacola.
- INEOS Britannia stayed ashore in Majorca.
Luna Rossa - LEQ12 - Cagliari, Sardinia - November 21, 2022
In Cagliari, the Italian Challenger Luna Rossa has emerged from the shed to undertake towing tests. They have been absent from the Gulf of Cagliari since November 6, when they dropped the mast on their LEQ12 prototype during a "simple mistake" while rigging ahead of a sailing session.
It was surprising that their LEQ12 would be up for a towing test after damaging their mast and maybe areas of the transom of the LEQ12. But the reason soon became obvious - their 12 metre long prototype AC75 was sporting sensors on one of the foils.
While not quite as sophisticated as those fitted to the British challenger, INEOS Britannia, the Italians are obviously after some basic information that their newly installed kit will provide.
It is not clear if the sensors were just attached for the towing test, or if they will be part of the more permanent setup.
"We're using this opportunity to do some changes and certain adjustments from the electronics and mechatronics that are a big part of the of the of this boat," explained Design Co-ordinator, Horacio Carabelli.
"In the towing, we can learn a lot from all this work that has been done. I think was very useful today, to put everything together, and to make sure that we are we don't lose any further time in the future when resume
"It has been really really productive and while the weather was a little bit windy for doing the test, but it was a good mistral and we had flat water, so we're pretty happy with the day."
On the new sensor on the port wing, he responded: "All the other teams know we try to sensor as much as we can in terms of of appendages. This is also part of our testing schedule now - to sensor where we can and when we can. "
He disclosed that the rig would be ready in the next week or 10 days - meaning the team will have been off the water for over three weeks. "In the next week or 10 days we will be back in the water fully rigged, and sailing and everybody happy with a new setup," he said.
Session Statistics - Cagliari, Sardinia - November 21, 2022 - Luna Rossa Prada Pirelli - LEQ12
Wind Strength 9-12kts (PM)
Wind Direction: SW (PM)
Sea State: Flat (PM)
Roll out: 0830hrs Dock Out: 1115hrs
Crane out: 1600hrs
Crew: Jimmy Spithill, Francesco Bruni, Umberto Molineris, Andrea Tesel and Marco Gradoni
Emirates Team New Zealand - LEQ12 - Auckland - November 22, 2022
A review of images in the AC37 Recon File System shows that Emirates Team New Zealand's LEQ12's nosedive took place between 1036hrs and 1040hrs yesterday, November 21 off the northern coast of Waiheke Island.
It's a nasty spot.
Wind readings yesterday, 4nm east of the capsize location showed that a strong wind squall moved through the area around 1100, with winds spiking rapidly to 30kts, and then dropping away rapidly. From photo meta-data of the AC37 Recon team images, the rain squall hit ETNZ's prototype AC75 at 1049hrs.
In a racing situation, the AC40 class would not start if the wind was above 23.5kts (using the 2021 limits), but in the 15-20kt range the AC40's (and AC75's) would definitely be racing.
The last photos of the AC40/LEQ12 before the incident show a moderate sea state, even allowing for the flattening visual effect of a camera lens which usually makes the sea state appear less than 50% of on the water impressions. By evaluating the photographic image against the sea descriptions in Admiral Beaufort's scale from 1805, the wind strength does look to be in the 15-20kt range.
Looking at video of the AC40/LEQ12 being towed home a much more active and confused sea state is evident, explaining a lot of the cause of the incident.
However the sea state is not exceptional, and should be have been within the capabilities of the AC40 in these winds of 15-20kts.
The sea state in the relatively shielded waters off Waiheke Island is quite different from 2metre swell, which caused the nosedive, in Barcelona, of Alinghi Red Bull Racing's AC75 earlier this month. The force of that impact was sufficient to rip the clew out of their jib.
An analysis of the images supports the Kiwi team's first impressions - that the bow was almost torn off during a violent nosedive as the LEQ12 went into a steep nose dive, while under manual flight control, and sailing at over 40kts.
The images reveal several creases running across the LEQ12's foredeck - usually a sign of severe compression from to structural failure.
While there is a mid-bow bulkhead, with two fire and aft girders behind, forward of that there is no internal structure and it appears that the bow of the AC40 is reliant on the monocoque strength of the complex bow shape of the AC40.
The failure is in some ways similar to the situation that occurred in the last America's Cup cycle, when the first run of supplied foil arms failed a destruction test at less than designed working load.
The solution to the foil arm failure was to devise a different method of construction, which was capable of withstanding double the designed maximum load - and successfully destruction tested that. But the process took six months for design, build and test.
The situation with the AC40/LEQ12 and indeed AC75, is that there is no reliable measured data for the loads experienced when a full bow shape nosedives at speed. It is therefore very difficult to run accurate tests to simulate destruction of a component or hull, in these extreme circumstances.
The team did stress testing of the AC40, when it was delivered in Auckland. There were no problems revealed. Usually part of that process is for audio sensors to be attached to surface of the test component. As can be heard in the foil arm destruction testing, carbon cracking noises are emitted in the run up to any catastrophic failure.
Passing that stress testing process would tend to rule out a building error, and means that the all AC40's produced to date will have a similar structural weakness in an extreme load situation.
Kiwis worst affected
As the first entry into the 2024 America's Cup, Emirates Team New Zealand had the first two building slots for the AC40's at the builder McConaghy Boats. They swapped one of those slots with the Challenger of Record, INEOS Team UK, who have the second boat, and Emirates Team New Zealand have the third AC40 which is en route to Auckland.
The immediate task for Emirates Team New Zealand's designers is to recheck their design models at the point of structural failure, and develop a repair specification to be retrofitted to the existing AC40's. A second task is to develop a new building specification for the AC40's that are under construction, or scheduled for build.
The complicating issue is that both the repair, retrofit and new build options must all produce a hull that meets the one design class weight restrictions. Usually this is done by the addition of compensator weights.
Emirates Team New Zealand, in placing its faith in the AC40 platform would seem to be the worst affected of the five America's Cup teams, with one boat that is damaged and must be repaired, and a second AC40 which needs a potentially awkward retrofit. Plus because they are only allowed one LEQ12 hull surface under the rules, their second AC40 must stay in one design mode.
Of the other teams, Alinghi Red Bull Racing is sailing its AC75 Boat One in Barcelona. American Magic have their AC75 Patriot sailing in Pensacola. Both Luna Rossa and INEOS Team UK have LEQ12 prototype boats that are launched, and are a separate operation from the AC40's.
Ironically Emirates Team New Zealand's first built AC75, Te Aihe, now owned by Alinghi Red Bull Racing, and designed with a submersible bow, survived a nosedive at 49.9kts on one of its last sails for ETNZ.
The silver lining in this cloud is that the structural issue around high speed nosedives with large volume bows, have been identified two years out from the 2024 America's Cup.
The structural stresses created by the sudden, and sharply angled, nosedive of a very buoyant bow can only be imagined. While ETNZ pioneered this design style for the AC75's, others like Italy's Luna Rossa have adopted a similar approach with the bow of their 12 metre LEQ12 test boat. In the light-moderate winds and sheltered courses of the 2021 America's Cup in Auckland the heavy air capability, and foibles, of the ETNZ AC75 design were not tested.
The other mitigating factor for ETNZ is that they have a highly competent in-house build team, probably the best in the world, who have been tested previously with these challenges.
The trade-off seems to be whether the team decides to do a temporary repair on the damaged LEQ12, and get it into a sailing state to be able to work through the list of new components and sails, that was posted the morning of the nosedive. Or, they can commission the new AC40, but cannot repurpose it as an LEQ12 test boat, and would probably also restrict their sailing to light and moderate winds, until the retrofit bow structures have been built into the hull.
The Kiwis only real option is to quickly resolve the structural design issue and repair their LEQ12 as soon as possible, and take a longer term view on rectifying the other AC40's, which can still be sailed, but not "red-lined".
Fortunately the call was made after the last Cup to keep the whole ETNZ America's Cup team together with various design/build projects like the hydrogen boat, and the land speed record challenge. The skills from this group form ETNZ's inner sanctum of experts, said to do its best thinking under pressure - and looks set to be called upon to do so once again.
Additional Images:
This commentary was written and compiled from video, still images and statistical content extracted from the AC37 Joint Recon program and other material available to Sail-World NZ including photo files, and other on the water coverage from the 2010, 2013, 2017 and 2021 America's Cups.