The ETNZ AC40 Suffers A Broken Nose

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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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AC40: IMPLEMENTING THE SOLUTION

Auckland - 25th November 2022

Just days ago, Emirates Team New Zealand buried the bow of their AC40 while testing in waves on Auckland’s Hauraki Gulf, which resulted in damage to the forward sections of the hull and deck structure. While the on-water team was recovering the yacht and returning to dock, the team’s engineers immediately began reviewing onboard data to identify the root cause of the issue.



“The first things we look at in this type of dynamic event are the accelerations and rotation rates that come from yacht’s inertial measurement unit (IMU),” explained Jamie Timms, Emirates Team New Zealand Structural Engineer. “These readings allow us to infer the magnitude of the hydrodynamic loads on the hull structure, which we can then input into our structural simulations to estimate the stress state and structural margins of safety. We also use the data to validate our fluid dynamics simulations of high velocity hull impacts.”

“During the 36th America’s Cup, we captured and catalogued the dynamics of every major event across the three yachts we sailed in that campaign and we enveloped those, with additional margin, to define the load cases for the AC40. Over the first 18 days of sailing the AC40, we’d seen a couple of events that generated large impacts. These had been lining up with our design load cases and the hull structure was performing as expected. However, this latest event saw accelerations that were far beyond all our previous records.”




“The figures below compare the longitudinal and lateral decelerations from the AC40 crash against the largest event seen by Te Rehutai, the team’s AC75 from the last America’s Cup (pictured above). “Not only did we see longitudinal decelerations 70% higher than the previous worst-case, but this was coupled with a simultaneous lateral loading of similar magnitude - the yacht came to a complete stop and yawed 90 degrees in just over a second. We believe it was this combined load state that led to an initial failure of the foredeck sandwich panel. The damage we saw in the hull and partial detachment of the bow structure is likely a consequence of the compromised deck panel, rather than a root cause.”


With this new data in hand, the team’s engineers have designed an internal structure upgrade package that will be rolled into all current and future AC40 yachts.

“Throughout the development of this class, we’ve seen the yachts become increasingly dynamic as the performance of the yacht and the skills of the sailors grows. As with any high-performance craft, there is a constant balance between reducing mass and ensuring reliability and safety, and as our understanding of the class grows, we evolve our approach to maintain that balance. This additional structure will restore full structural margins for the uprated load cases and allow the sailors to push the performance limits of the class safely and with confidence.”


The internal structure upgrade package will be built by McConaghy’s, who are building the fleet of AC40’s.

“The good news is there will be no change to the delivery schedule to the remaining AC40s currently in build and the bow upgrade package will be shortly sent from the McConaghy yard for retro fitting to the three AC40s that have already been delivered.