America's Cup: Emirates Team NZ sailing at 50kts - Video and on-board audio
by Emirates Team NZ/Sail-World.com 16 May 2023 09:38 AEST
Emirates Team New Zealand sail their AC75 Te Rehutai in Auckland, New Zealand © James Somerset / Emirates Team New Zealand
Yesterday, May 15, Emirates Team New Zealand wrapped up a 19day testing block with their America's Cup champion AC75, Te Rehutai, which has been upgraded to comply with the key requirements of Version 2 of the AC75 Class Rule.
Outwardly the key changes relate to a lighter overall weight, accomplished by various means including a crew reduction from 11 to eight; removal of the Code Zero and bowsprit, removal of the running backstays, removal of jib winches and replacement of the hand/arm grinding pedestals with cycle powered means of hydraulic pressure generation.
Above the deck there has been numerous subtle changes tidying up the aerodynamics and reducing parasitic drag as much as possible.
The other significant change is that the eight crew operate out of individual "foxholes" and are well protected from the 50-60kts of apparent windspeed, and driving spray, as well as lowering the windage from the sailing crew. In that regard there is no transfer of crew from side to side during/after tacks and gybes.
The launch of the above deckline reshaping of the AC75, has given the ETNZ designers a good insight into the nuances and options available in a Version 2 AC75, ahead of signing off the design for their 2024 AC75 raceboat.
Of course, the question is always - what is the top speed? Most teams will now admit/claim they are hitting 50kts. Most of the Recon teams who must be supplied with chase boats capable of 45kts, report being dropped by their prey - even when hitting speeds of 47kts.
Boat speed is a function of windspeed with top end boat speeds being a function of 3-4 time windspeed - which at 50kts of boat speed means that windspeed must be a minimum of 12 kts and maybe the top end of around 18kts of windspeed. Only the teams know what happens with their boats in windspeeds higher than 18kts - as the accompanying seastate is daunting for the chase boats, while the foilers will cut through it with ease.
To our eyes, the critical aspect of the new AC75's is their take-off abilities in a minimum windspeed (with races losing their wind speed constraints in the last 3-4 minutes before the start). And even more so after the start if the wind drops below the limit and one or both competitors drop off their foils. It then becomes a race to get foiling and be sailing at speeds of 20kts greater than your competitor. Arguably the last America's Cup turned on this key point of difference rather than top end boat speed - which in practice is a function of the wind pressure a team is able to find, than a design nuance.
However that said the key barrier to top end speeds is cavitation on the foils - and claims by the teams that they have regularly gone through the 50kts barrier indicates that some progress has been made in lifting the physical limitation of cavitation.
Emirates team New Zealand have not trialled any new wingfoils on the AC75, and are using legacy foils from the 2021 America's Cup. They have fitted a longer rudder - also a legacy item from the 2021 America's Cup.
For the record, American Magic held the top speed in the 2021 America's Cup of 53.31kts set in the Semi-Finals of the Prada Cup, during a gust and a bare away - broaching in spectacular fashion a few seconds later after their rudder ventilated.
We will run an assessment of the ETNZ program in the coming week, based on what we saw on the water of the team in the last Cup, what we have seen on the water and from shore in the current Cup cycle, and what has been picked up through access to the Joint AC37 Recon program.
In this video shot onboard and via drones, ETNZ show the AC75 sailing at speeds claimed to be in excess of 50kts.
"With the blink of an eye, two months sailing Te Rehutai in Auckland has gone in a flash," says the team in the blurb accompanying the video release.
"It may not seem like much - but the testing and development benefits has far exceeded the expectations for the team. But now, it is time for the great migration of Te Rehutai for a long northern summer ahead getting used to the unique characteristics of the waters to Barcelona."