A major change in the America’s Cup AC75 foiling monohull concept is the return to a soft mainsail, but with a twist . . . Double-skinned mainsails.
OUT are the semi-rigid 23 metre wings that were used on the 50’ ACC catamarans, IN are the new double-skinned mainsails that are now raised and lowered 26m to the top of the mast.
The revolutionary new design brings some of the aerodynamic advantages of the wing into the traditional sailing world.
Not that all has gone smoothly in introducing the double-skinned mainsails on this size of boat and at this level of competition.
Not only does it require a new mast configeration to handle the two mains, but the new mainsail configurations also involve complex batten, boom and mainsheet control systems, with the decksweeper style foot also adding to the deck layout and crewing complexity.
Although the decksweeper concept – to gain an ‘endplate effect’ by sealing off the bottom of the boomed sails to the deck – has been seen on F18 and A-Class multihull single-skin mainsails, there introduction on boats the size of the AC75 and in a double-skin format is a game-changing step.
Getting it right will be crucial to winning this America’s Cup.
The two ‘sail skins’ that constitute the mainsail are attached to the rig, one to each corner of the back of the D-shaped mast section.
It’s a 3Di product from North Sails, made from carbon fibre and equipped with buoyant material or airbags at the top, to provide buoyancy in case of capsize. The rig is one design, developed and produced by Southern Spars.
Each team can produce up to 10 mainsails under the rules and along with the mainsail you have the jibs and code zeros.
There are five jib sizes to accommodate the different conditions and they weigh around 60kg each.
Unlike the main, they are a single skin construction. The code zero – in effect an asymmetric style spinnaker – used in lighter sailing conditions, has replaced the traditional spinnaker on the downwind legs, but could also be used upwind when it’s very light.
The previous wing concept was complex and required a specialist operations team and a crane to attach it to the platform.
The new mainsails need support from more traditional sailmakers and allow the team to change sails on the water.
The INEOS Team UK sailmaking team is three strong, headed up by Sail Loft Production Manager, Ian ‘Shinzy’ Pattison alongside sailmakers Sam Haines and Danny Leech.
Shinzy has campaigned with numerous Cup teams, whereas for Sam and Danny the AC36 will be their first.
Sam Haines has over 20 years of sailmaking knowledge and provides some insight into the new sail concept:
“The nice thing about this type of sail, compared to the previous wings, is that it does bring back the more traditional skills and machine work, which I think some people have been missing in the previous editions.”
“The mainsail is the biggest sail on the boat; it is the primary device for controlling and powering the boat. It’s the equivalent to having a rudder in the sky! Iain [Jensen] is our trimmer onboard, there’s a lot of controls that primarily attach to the top (head) of the sail, including the twist and camber control.”
“These controls have a big impact on the balance of the boat, and the mainsail trimmer must work very closely with the helmsman to control the boat and keep it going fast.”
“We are still in a development phase and looking at different concepts and set ups. However, a lot of the thinking has come from how the wing sails worked, so we are trying to adapt this concept into the soft sail. We are really going to be pushing the boundaries.”