Cup Spy - April 13-14, 2023: Kiwis take on two Cup game breakers
by Richard Gladwell/Sail-World NZ 15 Apr 2023 16:59 PDT
15 April 2023
Emirates Team New Zealand fires up the Rangitoto shore - AC75 - Day 11 - Waitemata Harbour - April 14, 2023 © Richard Gladwell / Sail-World.com/nz
Off the back of the last America's Cup all teams have two major work-ons which are critical to their success or otherwise in the 2024 America's Cup in Barcelona.
The first, the stickiness of the AC75's, in light winds, became apparent in the America's Cup World Series event sailed in Auckland in mid-December 2020.
Stickiness is the AC40/AC75's ability to lift itself from displacement to foiling mode in light winds. It's the difference from sailing at speeds of 15-16kts as a displacement boat, to 25-55kts as a foiler. There's a variety of factors involved including wingfoil design, hull and foil drag, rig power, overall weight (lighter is better) and the skill of the crew. Parasitic or aero drag really only comes into serious play once the AC40/75 begins foiling, as does foil cavitation. Both factors are more a constraint on top-end speeds, rather than being factors which affect the AC40/AC75's ability to self-launch onto its foils.
In very simple terms self-launching onto foiling or flight is similar to an aircraft getting airborne off a runway. Both need to hit a takeoff speed, and then lift into the air. In the case of the AC40/AC75 takeoff speed is about 16-18kts. The design/sailing team's objective is to get this takeoff speed as low as possible, due to the obvious speed gains in flight when the foilers can travel at three/four times the windspeed.
As the Prada Cup and later the America's Cup proved - some AC75s were more sticky than others, and the British were the stickiest of all. But they were impressive in the first round of the Prada Cup, when there was plenty of breeze, and they won four races to become the first Finalist in the Prada Cup.
Arguably the outcome of the last America's Cup turned on the outcome of Race 8, when both competitors dropped off their foils for a substantial time, trying to round the windward mark laid in the wind and spectator fleet shadow of Motuihe Island.
Emirates Team NZ staged the best recovery, went on to win the race, and a scoreline which mid-race was going to be 4-4, was 5-3 at the finish, and winning the America's Cup became a much more difficult task for Luna Rossa.
The other issue is the ability of AC75s to sail in a seaway, which was only apparent for an hour or so on Day 3 of the Prada Cup Round Robin, when Luna Rossa raced INEOS Britannia.
It has become more noticeable in the 2024 America's Cup buildup, with the flight control issues on Alinghi Red Bull Racing, which were initially put down to the awkward seaway at the 2024 America's Cup venue.
However, as time has progressed, we had seen American Magic take on a volatile sea state on their last sail in Pensacola, when they took their AC75 Patriot out into the Gulf of Mexico for its final day - and without problems. A look at the video of Patriot shows the AC75 pitching significantly while at slow speed, but once foiling, the AC75s look comfortable - if ever that word can be used in their context.
Over the last two days in Auckland, we have seen the defending champion, ETNZ's Te Rehutai, now upgraded to Version 2 of the AC75 Class Rule, test their light air stickiness and, the following day, take on a seaway in a moderate to fresh breeze.
On Friday, the light winds of Thursday gave way to a fresher onshore breeze which often occurs at the beginning and end of the Kiwi summer. Watching from the shore, Friday's big breeze performance by the Kiwis in the AC75 was impressive - accepting that you are watching a boat sailing alone, free of racing pressure and considerations.
We didn't see the AC75 when it headed deep out into the Hauraki Gulf in a fresh easterly breeze. The AC37 Recon Team put the wave height at 1.8-2 metres, and Peter Burling afterwards, there were no issues on board the AC75.
I did see ETNZ for the last 45 minutes of the Friday session when the wind increased, and the team came into more sheltered water in the Rangitoto Channel (Course B from the 2021 America's Cup), changed down to the J5, their smallest jib, and did several upwind/downwind runs. The speed and stance of the AC75 was missile-like, and perfectly trimmed. The AC75 was fully stretched with an impressive fine mist of high-speed powder spray extending for several boat lengths astern.
It's a fair bet that the AC75 is hitting around 55kts in these conditions, and maybe can hit that speed in maybe just 15kts of wind. The fastest speed for a foiling yacht in a race is held by SailGP with an F50 hitting 54kts. In the 2021 Prada Cup, American Magic hit 53.31kts during the 2021 Prada Cup Challenger Semi-Final - which was the top speed of any of the four AC75's during the regatta. But there is a big difference in being able to hit a speed of that magnitude in a sustained way on a downwind leg, rather than just achieving a speed spike during a bearway and going out of control soon afterward.
As an aside, for some obscure reason the AC teams have a long history of not disclosing top speeds. During a media conference in Bermuda, at the end of the 2017 Challenger Qualifiers, all teams were asked to state their top racing speed. None would do so - except for the French - who had just been eliminated and were on their way home, and admitted to 40kts. Of course, the offset to the teams' mute response, is that in the televised racing coverage, viewers and rival teams get to see the individual boat speeds, in real time, on the TV screen. So why play secret squirrel?
But we digress.
"We headed out around Tiri and saw some pretty big swells and seaway and definitely looked like a lot tougher day to be on the RIB than the AC75," Burling said.
"It was quite bumpy out there at times. But seeing what these big boats can do in that kind of seaway is really cool."
A surprising comment from skipper Peter Burling came in the dockside interview after Friday's session when he mentioned that the team intended to train next week. The forecast is a sea of red - meaning winds in the 20-30kt mark. Over this weekend and during the week, a big seaway will build - and according to Burling, Emirates Team New Zealand intend to see if they and the AC75 can handle the conditions.
Sailing on Course A next week is a very ballsy call - and clearly, the Kiwis are looking for the answers to some hard questions ahead of sailing at Barcelona.
"Today was an awesome day for our program. We've been waiting for these north-easterlies," Burling told the AC37 Joint Recon team, "although it was probably a bit more easterly today for quite a while."
"We tried to get out in a bit more waves. And it was awesome."
Asked how close they got to being out of control, Burling replied "You never really know how close you are until it goes properly wrong. And we didn't have any of those situations today. So it was nice to get the boat back into one piece."
"We're cycling through a few new components, so it was great to get through the Job List and get the boat back into the pen and back into the shed."
As for Friday's windspeed: "We saw over 20kts times, but a lot around more like 14-15kts. We had the most breeze of the day on the way back into the harbour when we checked out the J5 jib."
"Obviously, with Barcelona, everyone talks about how big the sea state is. We can utilize that when we get the opportunity. And it was great to get out today, before next week, when it looks like it will be even more. "
"It was great to be able to check the systems today and make sure everything's all good to go for next week."
"Next week, it's looking like we're setting up for this easterly/northeast flow looks like we've got four or five days where it sits above 20kts," said Alistair Moore of the AC37 Joint Recon Team. "So that's going to generate a decent sea state out there. Is the plan to go out there and use that next week, Peter?"
"Yes, we're looking forward to going out and checking on the other end of the spectrum," Burling replied. "It's just great to see the boats in that sea state, and obviously, it's something that not many of us put in a massive amount of effort into for the last America's Cup, but it's something we've got to deal with this time around. So it's an exciting new challenge for everyone on the team."
Previously, the team had a good day on Thursday in light winds. The weather in Auckland has often been light, building to something more substantial later in the day.
Te Rehutai, which has been upgraded from Version 1 of the AC75 Class Rule to Version 2. She should be several hundred kgs lighter than in the 2021 America's Cup, and that weight reduction is apparent with the AC75's looking to be less sticky than in the 2021 Cup. The boat is not being sailed under the pressure of racing conditions, however, you rarely see Te Rehutai towed onto its foils, aside from maybe at the start of a session, if the expected breeze has not eventuated.
A feature of the way Te Rehutai is sailed is how close it flies to the surface of the water - with the separation between the underside of the hull and the surface being imperceptible and without the inevitable sea surface contact when AC75s are flown this low. That ride height consistency raises the question of whether the boat is being flown on automated flight control rather than manually by the crew - which is required under Cup racing conditions.
A key factor in the flight control paradigm is how to handle a seaway while foiling, up and downwind. That is the issue that will be addressed in the coming days on the Hauraki Gulf. It may well be that the problem doesn't exist in a boat sailed by a top AC75 crew. Certainly those in a RIB who have tried to catch/keep up with an ETNZ foiler know that the foiler wins hands down - every time.
Emirates Team NZ - AC75 - Day 11 - April 14, 2023 - Auckland
From the AC37 Joint Recon Team [Alastair Moore AC-Recon]:
Te Rehutai had her rig stepped and was in the pen just after 9, an earlier-than-usual dock out of 10 am due to the forecasted breeze build in the afternoon.
She was towed out to just NE of North Head where the yacht came to a stop and took Chase 1 alongside for the hoist. The main sail was on the lock at 10.25 with the J4 following, on its lock by 10.32.
At 10.41 Te Rehutai was off chase and building way in 14-16 knots of ENE breeze. On starboard tack, she was on the breeze heading for the southwestern corner of Rangitoto. Just east of the shipping channel she bore away at break neck speed heading for Takapuna Beach where she hardened back up again on starboard heading just north of Rangitoto light house.
She kept on with this up wind on starboard, down wind on starboard until she was off Murray's bay where she hardened up again and started a true beat with approximately 10 tacks out towards the east of Tiritiri Martangi Island. Here she came to a stop at 11.28 with Chase 1 only along side momentarily to swap out crew. By this time and in this location, the sea state was such that having a chase boat alongside would have been unseamanlike.
Peak wave height was approaching 1.6M with a very short period of approximately 6 seconds. At 11.44 she was sailing again with a short hitch to windward and then a long run back towards the East Coast bays with about 6 very smooth gybes observed. Te Rehutai now came to a stop for a lunch break and power group rotation. The break was from 12.09 to 12.41. The yacht now continued windward leeward testing but not going as far out and completing more laps.
She headed for the shelter of Rangitoto channel and came to a stop at 13.03 where I watched the J4 come down and the J5 go up. She was off the chase boat and sailing again by 13.18 now staying just inside the channel and doing several zigzag runs north to south or south to north. Again Te Rehutai out did us in the recon chase boat for speed. Even in the relatively flat water of Rangitoto channel tapped out she was at times 10 knots quicker than us. [SW: Top speed of the Recon RIB has been previously stated to be 47kts - it is one of the umpire boats used for the 2021 America's Cup)
At 13.44 she came to a stop just north of Rough Rock (north of North Head) where she dropped sails and was towed back to base arriving at 14.15.
Today was spectacular to watch but tremendously difficult for the cameraman! Lots of crash, bash and splash.
Session Statistics - Emirates Team NZ - AC75 - Day 11 - April 14, 2023 - Auckland
- Weather: 19°C 50% cloud cover
- Wind Strength: 12-18kts building to 22kts
- Wind Direction: SE
- Sea State: 1.0 - 1.5mtrs
- Roll out: 0900hrs Dock Out: 1000hrs
- Dock In: 1415hrs Crane out: 1500hrs
- Total Tacks: 29 - Fully foiling: 28; Touch & Go: 1; Touch Down: 0
- Total Gybes: 17 - Fully foiling: 17; Touch & Go: 0; Touch Down: 0
Crew: Nathan Outteridge, Peter Burling, Andy Maloney, Blair Tuke, Simon Van Velthooven, Marius Van Der Pol, Louis Sinclair, Louis Crosby, Hamish Bond, Marcus Hansen, Sam Meech
Emirates Team NZ - AC75 - Day 10 - April 13, 2023 - Auckland
From the AC37 Joint Recon Team [Alastair Moore AC-Recon]:
The race yacht was on the docks edge by 10.59 and was rigged and in the pen by 11.35.
The usual team meeting was watched from the RIB with Ray Davies and Peter Burling running it.
She was towed from her berth and just outside the break wall the main was hoisted with it dropping onto the lock at 13.38.
The J2 was hoisted next. She was off chase by 13.55 but due to very light air up the harbour she was taken in tow again and brought out to Rangitoto light where she dropped the tow at 14.22 in 6-9 knots from the NNE.
Her first tack was a dud touching down just after sails were across.
35 seconds later she was back up and foiling. After one upwind and one down she came to a stop at 14.35 and changed to the J1.
This was on the lock by 15.06 and she was sailing again at 15.09. Another up wind and down and she stopped again at 15.21. Here a power group rotation was observed.
At 15.27 she was off chase and sailing again out just past A buoy running in towards the southern end of Takapuna three times before stopping again at 15.49 where she changed from the J1 to the J2 and was sailing again by 16.06.
Another two windward leewards were observed before the yacht came to a stop north of Rough Rock (just North of North Head) to lower sails. She was back in the pen by 17.00
A good light airs day.
Session Statistics - Emirates Team NZ - AC75 - Day 10 - April 13, 2023 - Auckland
- Weather: 22°C 20% cloud cover, Sunny
- Wind Strength: 5-10kts
- Wind Direction: Variable
- Sea State: Slight
- Roll out: 1135hrs Dock Out: 1330hrs
- Dock In: 1700hrs Crane out: 1730hrs
- Total Tacks: 16 - Fully foiling: 15; Touch & Go: 15; Touch Down: 1
- Total Gybes: 20 - Fully foiling: 20; Touch & Go: 20; Touch Down: 0
Crew: Nathan Outteridge, Peter Burling, Andy Maloney, Blair Tuke Simon Van Velthooven, Marius Van Der Pol, Louis Sinclair, Louis Crosby, Hamish Bond, Marcus Hansen, Sam Meech