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America's Cup - Glenn Ashby on hitting the AC50's sound barrier

by Richard Gladwell, Sail-World on 18 Apr 2017
The AC50 will hit speeds of over 30kts in the sub-10kt wind range Richard Gladwell www.photosport.co.nz
'A couple of years ago it was hard even to imagine having a potential race boat. It has been a tough journey, but an interesting one,' said Emirates Team New Zealand skipper, Glenn Ashby, as the team prepares for their first sail in Bermuda.

'Now we have last part of the journey to experience over the next few months.'

'We have to go racing at some stage, and now is that time.'

'I think the other teams are still in a big development phase in terms of their program,' he said comparing the New Zealand team to the other five - some of whom have been in Bermuda for the past two years.

'We have been racing ourselves in Auckland and have 15 people in a chase boat who all think they know how we should be going! We certainly don't lack for feedback!' he laughed.

'Now, we are looking forward to being in a position where we can put our race hats on.'


The Kiwis were the the last team to arrive in Bermuda. While Emirates Team New Zealand are the longest established team in America's Cup history, in this the team's ninth AC campaign, the Kiwi team have polarised the others, Challenger and Defender alike, as no Challenger has done in Cup history.

For the 35th America's Cup, it will be Emirates Team New Zealand who will be wearing the Black Hat normally worn by the Defender. But it is a badge of courage for the only Southern Hemisphere team in the regatta, and matches the country's All Black colours and sporting tradition.

'We almost look at it as an advantage at the moment,' says Ashby. 'Those other guys see each other every day. They are sailing against each other every day. They are in their own little world.'

'We are either going to come in, in good shape, or having plenty on.'

'If we have made all the right decisions on the way through hopefully we will be in a strong position. But even so, we have a big development program in Bermuda and will hopefully be developing right the way through to the final. It is a never-ending quest for performance and chasing the ultimate speed.'


That development quest is the same is a lot of high-speed sports, and Ashby compares the America's Cup program with Moto-GP or F1.

'It is in the testing during the off-season where you have most of your thrills and spills,' he explains. 'When it comes race time, hopefully, you are nice and smooth, and you know your settings really well. That's definitely the program at the moment.

Finding the limits in the big breeze
'When you are sailing in the breeze, you have to learn to sail hard and fast in those conditions. You are pushing to find where the edge of those limits are - and a few skids and wobbles is par for the course.'

'Knowing when to button off and be a bit safe is probably more on my shoulders than the younger guys because they are all happy to keep pushing hard. Sometimes you need to pull the reigns back for the safety of the campaign.'

The biggest breeze Team New Zealand have seen to date is over 25kts.

'That's plenty for us, ' Ashby chuckles.

Top end speed to date has been in the 'mid to high 40's' he says, replying to the inevitable but obvious question.

'That's ticking along,' except this time the accompanying chuckle has a slightly nervous edge to it.

'The AC72's did a similar speed in those sort of conditions. So you run into a bit of a wall at those speeds. You don't go a lot faster with the foils that we have designed. If we did some super-cavitating foils we could go right past 50kts, but we would be slow around the rest of the track.


On both AC72 and AC50 Ashby explains the cavitation on the foils limits the top end speed along with the drag.

'You just run into a bit of a 'sound' barrier where you need a lot more thrust to go a little bit quicker.'

Externally Ashby says it is not possible to see the cavitation manifesting itself through increased spray, white water or similar - making spy-boat photos a little redundant.

'It is only possible to see it with on-board cameras. If you are on the boat and see that the speed is in the mid-40's you know that you are well into that zone.'

AC72's half the speed in mid-wing range

The big difference between the AC72, the America's Cup Class, used in the 2013 America's Cup in San Francisco and the smaller AC50 to be sailed in Bermuda, lies in their light and medium air performance.

'These boats are incredible. The performance that can be achieved in light airs is the amazing thing. In 7-8-9-10 knots of breeze, you are sailing at 30kts at times.


'In the AC72 you would be half that speed in those conditions', he adds.

'The AC72 would be fully displacing upwind and maybe doing 15kts, in the AC50 were are doing 25-26kts upwind. It's a really different feel.'

Emirates Team New Zealand are expected to be on the water and sailing Bermuda, this week.

There is no word yet on whether they will participate in Practice Race sessions, or if they will race against Challengers only on those race days.

Kiwi fans at least, will be hoping over the coming three months, that the high pitched whine of hydrofoils at speed will be replaced with the occasional sonic boom echoing around the Great Sound in Bermuda.

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