The cutting-edge "flying" yachts created for next year's America's Cup will be tested in race conditions for the first time when a series of warm-up events begins in Auckland on Thursday. The 23-meter (75-foot) yachts feature innovative foil arms, which lift the hull above the surface of the water into the air, reducing drag and increasing speed.

In full flight, the yachts exceed 50 knots while the entire vessel is balanced precariously mid-air on carbon fiber foils.

Team New Zealand skipper Glenn Ashby said he felt like an astronaut when sailing the defending champion's boat, Te Rehutai. "It is a boat and it has to go through the water, but it's also a flying machine," he said. "The hairs on the back of your neck stand up when this thing goes in the water."

Ashby led the Team NZ campaign that won the America's Cup in Bermuda in 2017, giving the Kiwis hosting rights for the next regatta in March 2021. The yachts used in Bermuda also foiled, but they were much smaller at 15 meters and had added stability because they were twin-hulled catamarans. The team NZ helmsperson said the new class of monohull yachts were bigger and faster than their predecessors, producing "knife-edge" sailing that pushed the foiling concept to the limit. "The margins of getting it right and wrong are pretty tight," Ashby said. "You're in control while being on that knife-edge, all the time you're deciding how hard you want to push things, there are definitely times you're a little bit out of control."

There are four teams involved in this week's warm-up events: Team NZ and the challengers Italy's Luna Rossa, American Magic and INEOS Team U.K.

There will be three days of America's Cup World Series racing from Dec. 17-19, followed by the Christmas Cup race on Dec. 20. Results will have no bearing on the America's Cup proper, it is more a chance to test technology and size up the competition in race conditions.

Aucklanders will also have the chance to watch the racing in the city's harbor from the shoreline for the first time, unlike previous regattas at the venue, which were staged well off the coast.

Defender TNZ appears to be the early pacesetter, dominating practice sessions, following by Luna Rossa, American Magic and Team U.K. Bookmakers have the New Zealanders as short-priced favorites for the overall event, predicting they will retain the trophy in March. But Luna Rossa skipper Max Sirena warned there was a long way to go, saying his crew would match Team NZ for "street-fighter" attitude. "It's too early for anyone to come up with a conclusion. For sure you have an idea, but I think it's too early, anything can happen," he told New Zealand media. Luna Rossa will have Australia's Jimmy Spithill at the helm, who humbled the New Zealanders when he masterminded a dramatic come-from-behind victory to claim the Auld Mug for Oracle Team USA in San Francisco in 2013. The three challengers will compete in the Prada Cup from Jan. 15 to Feb. 22 for the right to race Team NZ for the Cup in March.