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America's Cup: Kiwi's AC40 nosedives causing structural failure

by Richard Gladwell/ 20 Nov 23:35 PST 21 November 2022
Emirates Team New Zealand AC 40 - November 21, 2022 © Adam Mustill / America's Cup

The issues of sailing foiling monohulls in top end conditions were underlined today, when Emirates Team New Zealand nosedived their AC40 during a training sail on the Hauraki Gulf and suffered substantial structural damage to its deck and bow sections.

The AC40 was towed home early afternoon, after exiting the inner Waitemata Harbour three hours earlier at around 1000hrs.

The breeze was blowing from a NW direction, which is an unusual direction but one which has been notable for several incidents with racing yachts, including the capsize of American Magic's Patriot on Day 3 of the 2021 Prada Cup.

It seems from a statement issued by the team that they had decided to test the AC40 in the knowledge that conditions were extreme in the area, off the northern side of Waiheke Island and approximately 16nm from Auckland.

Auckland has been subject to some severe weather over the past few days, including waterspouts, and severe rainsqualls in the Hauraki Gulf and Rangitoto Channel.

Today the conditions were relatively sheltered in the Rangitoto Channel with several cruising yachts sailing and looking comfortable in the conditions.

However in the area chosen by Team New Zealand for their testing, readings from Predictwind recording stations indicate that winds in the mid-20kts range were recorded around 1100hrs and again in the early afternoon. According to Predictwind, a 30kt+ rain squall was recorded in the area around 1100hrs just before/after the AC40 capsized.

A search of AC37 Recon Team images - using the metadata for each image shows that the AC40 was sailing at 1040hrs and was capsized three minutes later.

The rain squall mentioned in the graphic below, was recorded 4nm west, of downwind of the capsize location, at 1100hrs, but as can be seen the wind increased dramatically. The team later claimed that the windstrength was only 15-20kts at the time which is confirmed by the sea state in the images of the capsize.

The recovery operation was not easy, however Emirates Team New Zealand have previous experience in these situations, it is their fourth known capsize.

Once it was righted, the GPS track shows the AC40 was towed to Matiatia, a sheltered harbor at the western end of Waiheke Island, presumably to get the water ingress issue resolved, enabling the AC40 to be towed home on its foils.

The yacht towed past North head around 1324hrs this afternoon, heading for haul-out at the team base.

It is not immediately clear what the effect of the incident will be on Emirates Team New Zealand's development program. The AC40 will obviously have to be repaired, but that should be possible in New Zealand using the team's own construction facility and building team. Normally new sections would be laid up in the original tooling to get the external shape accurate, and bond these in place of the damaged sections. However the tooling is with builder McConaghy Boats in China.

The team had, today, posted a schedule of parts that were to be tested which included sails. Obviously these test plans will be delayed by the fallout from the nosedive. The team is taking delivery of a second AC40 in December, which will require strengthening in the bow area before it can be sailed by the team.

The damage is a separate issue to the tribulations of sailing foiling monohulls in a seaway.

Last week, swells of around 2 metres were reported at Barcelona, during a day in which it was too light for Alinghi Red Bull Racing to sail.

The Swiss team, sailing Emirates Team New Zealand's former AC75, Te Aihe, have nose dived spectacularly on other at least one other occasion in Barcelona, with the AC37 Recon Team images showing the AC75 with its rudder elevator clear of the water. There was sufficient force generated by the nosedive to blow the clew out of the AC75's jib - making a spectacular image.

No crew have been injured in either incident.

A statement issued Monday evening by the team reads:

Emirates Team New Zealand have suffered damage to the bow of their AC40 today after an early start testing on Auckland’s Hauraki Gulf in some top end conditions.

In recent weeks the Emirates Team New Zealand AC40 has been taken out of its one design configuration and testing stepped up in its development and data collection towards the design of its AC75.

The team were testing under manual flight control to the north of Waiheke Island in around 15-20 knots of windspeed and large waves. While sailing downwind at over 40 knots of boat speed, the crew onboard lost control of the ride height which caused the rudder and elevator to come out of the water. This resulted in a high-speed uncontrolled gybe and simultaneous deep nosedive followed by a capsize.

The resulting impact of the water pressure collapsed the foredeck at the bow of the AC40. Significantly the watertight bulkhead aft of where the damage occurred maintained its structural integrity, successfully serving the purpose of controlling water ingress so the boat could be righted and towed back to base.

Within moments of the incident, the team on the water and design and build team back at the base were well into a program to assess the damage and repair timeline but also importantly understand the precise loads on the structures in the incident and lessons that can be learned and implemented going forward.

Emirates Team New Zealand CEO Grant Dalton said, “It appears that when the boat nose-dived, which was the best we have done, the high water pressure and side load collapsed the forward section of the deck causing the resulting bow damage. The designers are analysing the load cases of the incident and although it might be too soon to tell, it is likely that we will have some retrofit structure necessary to our boat and throughout the AC40’s fleet. But we will understand this further in the coming days.

The AC40 was towed back to base on its foils after the incident and is back in the shed being assessed for the repair job ahead.

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