Team New Zealand reveal the soft wingsail breakthrough they are testing for the next America's Cup boat.

Team New Zealand's design geniuses are at it again, producing a ground-breaking soft wingsail for the revolutionary foiling monohull to be used in the next America's Cup.

And they have proven true to their edict to produce state-of-the-art technology that can trickle down to the average yachtie.

Last week they secretly tested a scaled down version of the new sail, popping the rig into a 22-foot non-foiling trimaran and ripping around Auckland's Waitemata Harbour.

EMIRATES TEAM NZ Team New Zealand trial the new soft wing sail concept on a 22-foot trimaran on Auckland's Waitemata Harbour.

It was a successful practical exercise to validate the promise shown in computer testing as Emirates Team New Zealand rush to get the class rule for the new AC75 boat in front of prospective challenging syndicates by March 15 and into the public domain on March 31.

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The concept being tested has a large "D" shaped section mast, developed and built by Southern Spars, with separate mainsails on either side, providing a smooth transition from the mast to sail in its aerodynamic shape.

EMIRATES TEAM NZ Team New Zealand's Tim Meldrum between the two sails that make up the revolutionary wing sail.

Once the mast is in, the sail can be raised and lowered in conventional fashion, eliminating the need for the daily crane work required to attach the hard one-piece wingsails used on the catamarans in the last two America's Cups in San Francisco and Bermuda.

Teams will be able to change sails while at sea and also lower the sails to be towed back to their bases, an important factor for Auckland conditions where the 2021 regatta is planned.

Designers from Italy's Luna Rossa syndicate, the official challenger of record, and representatives from Southern Spars and North Sails, witnessed the testing that saw Glenn Ashby, himself a sail expert, on the tiller for the two days of trialling.

EMIRATES TEAM NZ Glenn Ashby checks the performance of the new wing sail concept during testing on Auckland's Waitemata Harbour.

It's a breakthrough concept for a simplistic wingsail and one that will help keep the top end of the massive boats light enough to enable them to self-right from capsizes.

"There have been lots of attempts at having what you'd call a thickened mainsail, more of a soft wing, but nothing has been done on this scale at all," Steve Collie, who is the mast and sails co-ordinator in Team New Zealand's design group where he has been involved in four Cup campaigns.

"The purpose of it wasn't really to test performance. The boat was very different ... a non-foiling boat and went at very different speeds and wind angles that we would expect to sail. We were more testing the mechanics, that we could get the thing up and down and how the shape set up. It was really promising."

EMIRATES TEAM NZ North Sails' Burns Fallow and Team New Zealand designers Dan Bernasconi and Steve Collie watch the test wing sail being put in.

The latest work comes fresh off Team New Zealand winning the innovator of the year category at last week's New Zealander of the Year awards for the "cyclors" concept that was a key element in their stunning success in Bermuda last year.

Team New Zealand design boss Dan Bernasconi was encouraged by the practicality and performance of the new rig and sail.

"It's gone really well. Like all tests, it's a learning experience and the point of it is to find out what is working and what needs to be improved. But we have taken a lot from it which we will feed into the class rule that we are drafting now," Bernasconi said.

He chuckled that they had certainly produced a new speed record for the trimaran that was used which was roughly a one-third scale. The actual mast of the AC75 will be around 28m.

Collie said there would be a one-design element to the shape of the mast and some of the structure but they were eager to allow development which they maintain is a key part of the America's Cup game and one where the Kiwis have continually excelled.

"It is early days. What we put out (in testing) is by no means perfect and when you get a few America's Cup teams working at this for a few years you will get a lot of advancement," Collie said.

"We will be racing these things in just over a year. I don't think they will be perfect by next year by any means. There is going to be a lot of challenges and a lot to learn. So we are trying to strike a balance between allowing some one design stuff but freeing teams up to push the development boundaries."

Collie was coy over the control of the wingsail. Don't forget Ashby's X-Box system that proved a key element to the Bermuda success.

But it appears to be a move back to more conventional mainsail trimming controls, while the concept allows for twist and camber control at the head of the mainsail through a control arm on top of the rig

"That is still relatively open ... what's practical with winches versus hydraulics? I wouldn't say it's going to be anything like the wing where we had complex control systems. We still want to keep these things relatively simple and retain the traditional elements of sail design.

"Essentially we are looking for a new advancement in mainsail technology that we would like to think can trickle down to other boats not in the America's Cup."