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America's Cup: Test sail of the AC75 rig - Video

by Sail-World NZ/ETNZ 24 Feb 2018 19:00 GMT 25 February 2018
Bella Mente Quamtum Racing graphic of double luffed AC75 mainsail © Bella Mente Quantum Racing

A small development team of Emirates Team New Zealand’s designers, shore crew and sailors, supported by Luna Rossa, North Sails and Southern Spars, have been busy developing a prototype soft wing sail and rig to be part of the AC75 class of boat to be sailed for the 36th America’s Cup in 2021.

The concept was first unveiled by Bella Mente Quantum Racing's Terry Hutchinson during a US Sailing Leadership Forum held on February 4. Hutchinson showed a graphic with the D-shaped, square backed spar supporting two mainsails each with its own track.

It is an attempt to get the some of the benefits of a wingsail, without the need to lift the entire rig out of the boat.

The big gain is not in performance but in handling the cranky AC75's which will have minimal stability when at rest.

The rig will enable the AC75's to be towed in a conventional way and not using the process known as "sideslipping" in the AC50's - where in any moderate breeze or above the chase boat was strapped bow to stern with the AC50 to get the foiling catamaran back to base.

Sideslipping was required on any tow that was not into the wind, as on reaching or downwind tows the wingsail could not be feathered and would power up, taking charge of the AC50 and its chase boat.

It is a very slow process and was necessary in Bermuda in most situations to get the AC50's back to the dock once they had entered the Royal Dockyard - requiring the 300 metres Dockyard to be closed to all other traffic to allow the AC50's to be "tacked" into their berth by the support crews and chase boats. The process could take up to 20 minutes depending on the wind angle and strength.

The downside of the concept is the bulk contained in the double sail, which will make interesting handling by the crew and can be seen as the sail is dropped in the video. (Remembering that the sail below is only on a relatively small trimaran and not an AC75, with a mainsail luff length about three times the length of the test boat in the video.)

Emirates Team NZ reported the test in social media:

“Although we have been working collectively and quietly developing this concept since last year, it is not a huge secret in terms of what we are doing because the intention is to have a tested rig and sail concept that will become part of the AC75 class rule.” said Project Co-ordinator Steve Collie.

“We have been developing this concept towards the class rule in Auckland with representation of the Challenger of Record, Luna Rossa’s designers here as part of the testing process.

The objective of the testing in Auckland is to validate a concept which the Emirates Team New Zealand designers have found to be promising in initial simulations.

North Sails and veteran America’s Cup sail designer Burns Fallow has been a key part of the process from the beginning.

“We started off back in August with a clean sheet of paper and some ideas and came up with this mainsail concept.”

“We have done enough work on it in simulation to know that it is a fast concept, but you have got to do the basic things like tack and gybe, and make the thing go up and down and just little things like that before you commit to this for the next three years.”

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

“In addition to conventional mainsail trimming controls, this concept allows for twist and camber control at the head of the mainsail through a control arm on top of the rig which will be very interesting for us sailors especially transitioning back from the AC50 hard wing sails.” said Glenn Ashby.

While the hard wing sails of the AC50’s were extremely efficient, they required 20 people to launch and retrieve the wing before and after each day’s sailing.

“We want something where teams can take the mainsail down and leave the rig in at the dock as well as potentially make mainsail changes on the water, but have something that aerodynamically is superior to a conventional mainsail without being heavier.” explained Collie.

“Essentially we are looking for a new advancement in mainsail technology that we would like to think can trickle down to other boats.”

As with all America’s Cup class developments weight is always a big issue, but especially so with the AC75’s because of their self righting ability it is important to keep weight aloft to a minimum.

After a handful of days testing the roughly 1/3 scale model on Auckland Harbour the initial tests proved pretty positive for all parties involved in the project.

“To see it in reality, even in the small scale it’s a big step in our confidence, that this thing is something a bit different and should be pretty good.” concluded Fallow.

“Obviously this is a very early concept and test, but the main purpose is validate that our thinking is heading in a realistic direction. It’s huge step towards the finalisation of the class rule which is due to be released on March 31st.” said Ashby

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