The wind has many moods on the Hauraki Gulf near Auckland's Waitemata Harbour where the 36th match for the America’s Cup is taking place between defender Team New Zealand and Italian challenger Luna Rossa.

It can be angry or elusive. In sudden squalls it can whip up white caps like cake frosting and in calms the Gulf can lie equally as limpid.

In daily competition, the west coast southwest sea breeze and east coast north-easterly sea breeze vie for ascendancy, egged on by the warming land. At the same time tides work against the wind and add to the puzzle the sailors of this America’s Cup have to unravel.

Indigenous Maori, the first to see the Gulf, called it Hauraki or North Wind. They also knew it as Tikapa Moana of the Mournful Sea, which might be more accurate for those who, in the coming races, will have to decipher the mystery of it winds.

New Zealand helmsman Peter Burling isn’t Auckland-born; he grew up two hours away in coastal Tauranga. But he has sailed on the Gulf and Harbour since he was nine years old and, like most of the New Zealand crew, has a deep understanding of these waters.

From his youngest days, before his Olympic gold medal in Rio de Janeiro in 2016 and his nine world championships, Burling learned to find the wind in the sailor’s manner, part by instinct, part by the signs on the water.

In the high-tech AC75 class yachts, foiling at speeds of up to 50 knots, those home-spun practices aren’t always practical. Teams rely on a vast array of historical, current and immediate weather data to make decisions in their design process, before races and on the course.

They have their own meteorologists and computers on shore and on board which crunch that data.

Knut Frostad, the former Olympic and Volvo Ocean Race sailor, now heads the marine electronics company Navico which provides weather sensors to America’s Cup teams.

“Wind is probably the single most important piece of data on the race course,” Frostad told the Associated Press. “Being able to identify changes and adapt accordingly can massively influence the boat speed and point of sail, especially on these superfast AC75s, so the degree of accuracy and speed of that information is critical.

“The faster the boat, the greater the payoff for finding more wind from better direction. In an AC75, finding one knot more wind speed can give you three knots more boat speed.”

America’s Cup boats have a bow sensor and mast sensor which supply data to onboard computers.

“That little piece of equipment is almost like the heart of the boat,” Frostad said. “Without it, it is essentially impossible to sail an AC75 to anything close to its performance.

“The speeds at which these teams are racing is absolutely incredible — something unheard of just a couple of years ago — and with the constantly changing conditions on the challenging Hauraki Gulf race course, the skippers and navigators are having to make split-second decisions using real-time speed and wind data at their fingertips that could have big implications on the race outcome.”

Team New Zealand has home advantage, the advantage of local knowledge and years of experience sailing on the Gulf. They can use historic data from the 2000 and 2003 America’s Cup in Auckland to project contemporary conditions.

They also have formed a partnership with New Zealand’s National Institute of Water and Atmospheric Research (NIWA) which uses its super computer to crunch wind and tide data and provide that to Team New Zealand for use in its simulator and in pre-race and on board decision-making.

Data from the NIWA computer is beamed aboard the New Zealand yacht during races, updating every 20 seconds and offering a comprehensive picture of winds and currents on the racecourse.

“It’s a human who drives the boat, let’s be clear. It’s Peter Burling who’s on the helm making those decisions,” NIWA’s Mike Williams told Radio New Zealand. “One of the important things we’re doing for them, and this is one of the challenges for us, is that we’ve had to provide them with current information because when they’re up on the foils they can’t measure the currents."

“To have a knot in the middle of a Cup race, or to have one knot on one side of the course and half a knot on the other side, of the course is a huge difference.”

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