Cup Spy: Kiwis answer questions on AC75 foiling in a seaway
by Richard Gladwell/Sail-World.com/nz 18 Apr 2023 13:57 BST
19 April 2023
Emirates Team New Zealand - AC75 - Hauraki Gulf - April 18, 2023 © Richard Gladwell - Sail-World.com/nz
Questions as to whether AC75s could be raced in a confused Barcelona sea state in the 2024 America's Cup were partially answered Tuesday by the America's Cup champions in a bleak four-hour sailing session on the Hauraki Gulf.
Since Friday, Auckland has been buffeted by fresh to strong easterly winds, which usually create a challenging sea state in the Hauraki Gulf, compounded by the effects of a 10ft tidal range.
The winds were still too strong for sailing on Monday, and today was the first opportunity to find out how the 69ft foiling monohulls could handle the seaway - with the expectation that there would at least be some spectacular leaps or nosedives if not a capsize.
For those unfamiliar with Auckland, the Hauraki Gulf is a relatively shallow area of water 75nm long and 37nm wide, covering an area of 1500 sq. miles. It only flooded to its current depth about 7,500 years ago. On its eastern side is the Coromandel peninsular and several significant islands.
Outside in the Pacific Ocean, a 2.5mtr (8ft) seaway was running.
Some of the ocean swells do come through, but generally, the sea state only really builds up when an easterly has been blowing for several days - and stays up through the night.
Barcelona may be different, but the Hauraki Gulf today was an interesting test and as good as it will get for ETNZ will get ahead of the real thing.
The Kiwis clocked out of the base at 1130hrs and towed down the harbour into a reasonably fresh easterly breeze of 18kts gusting 20kts and bright sunshine. They stopped at Northern Leading (a navigational light) with wind recording devices which is probably the most accurate gauge for sailing - being only 8 metres above sea level.
With sails up, they headed down to Course E, between the mainland and Waiheke Island. The sailing area is near landlocked but also subject to some of the worst wind against tide conditions in the Gulf.
This was the location used in the 2021 America's Cup on Day 4 when both Luna Rossa and Emirates Team NZ both came off their foils in light winds in the wind shadow of the former quarantine station and prisoner-of-war camp on Moutihe Island.
From what we could see (using 14x and stabilised binoculars), they did a couple of warmup laps, up, down and across the wind, without any issues.
With the breeze increasing to 19-20kts and gusting higher, the murk closed in from out to sea and to the north. Usually, these are not great natural signs and indicate worsening weather.
In the end, while the wind increased slightly, its only real effect seemed to be to maintain the sea state, and further out, there was plenty of white breaking water, indicative of a ground swell coming through with substantial wind chop on top.
These are normally tough but good sailing conditions in the dinghy classes. Upwind it is punishing, with the breaking seas, but downwind you get some great Southern Ocean-style rides.
These were far worse conditions than we saw in the last America's Cup - even on Day 3 of the Prada Cup when American Magic had their spectacular capsize in what was then an offshore breeze. In a couple of the starts previously between Luna Rossa and INEOS Britannia, the wind and swell/chop were more pronounced than in the fateful race and caused both AC75's problems going upwind, with difficulty in staying foiling and some spectacular splashdowns/submarining during mark roundings.
After what looked like a cautious start, today, the Kiwi's confidence grew as the AC75 was put through its paces. The outcome was remarkable, with the Te Rehutai appearing to handle the conditions easily and with the chase boats unusually hanging back in the seaway.
The foiler appeared to be having a far easier time of it than would be the case in a keelboat.
We watched the four-hour session for about three hours from various elevated vantage points and could easily follow the action with binoculars.
The limitation on cliff-top viewing positions is that you can't see the close-up action, but you get a big-picture view of the sea state, wind direction and strength - which can easily be checked in real-time.
The only question was whether the AC75 was being sailed at flat-water race pace on the open sea. Te Rehutai didn't look as quick as it did on Friday, but the light was quite different, and today's haze/mist was not conducive to detailed viewing.
The trim of the AC75 was, as always, near perfect - which always raises the question of whether it is on automatic flight control.
Upwind, the AC75 appeared to be sailing normally, as it would in winds of 15kts and flat water. Several short, racing-length legs were sailed - with most tacks being dry and with none of the splashing and crashing we'd seen on Day 3 of the 2021 Prada Cup as the two AC75s trued to go uphill.
At the top of each leg, the Kiwis seemed to handle the bear aways with relative ease. The AC75 could visibly accelerate through the so-called "Death - Zone" in a smooth action. We didn't see any serious splashes from foil arms digging in or nosedives, which are clear long-range indicators that the crew are on the edge of control.
Maybe the view from close-up was different, but we didn't see any spinouts.
There was some surfing with the AC75, occasionally running a very deep angle. The bow did drop in - but the flare did its job.
For the rest of the week, the breeze is expected to lighten a little but stay in the same direction - and the seaway will build, and Emirates Team NZ are expected to conduct more AC75 testing.
Wind information