This article was first published on northsails.com, January 2021.
By Rebecca Hayter
When Sir Ben Ainslie described the cunningham as a key setting in the power of his AC75 Britannia, a delayed shock ran through the viewers watching the America’s Cup racing.
Ken Read, CEO of North Sails, understands the confusion and took the opportunity to explain North Sails Helix technology.
'For most yachties watching, a cunningham is a little string on the luff of the mainsail, just above the tack,' he says. 'You pull it down; it tightens the luff, and that’s your upwind mode. You let it off for downwind mode.'
Not so in the 36th America’s Cup. In this new age of the AC75 foiling monohull, the little cunningham has a big job.
It takes some serious power to lift the 6.5-tonne AC75 at speed from displacement hull to foiling machine. Initially, the AC75 needs massive depth in its mainsail to generate power for lift-off. As soon as the boat is foiling, that depth becomes drag and the mainsail needs to be flat. As the boat accelerates further, the mast is raked back and the sail flattened even more.
In just seconds, the boat has progressed from low-speed displacement sailing in 10 knots apparent wind speed to high-speed foiling in up to 70 knots apparent wind speed. Throughout the race it will constantly adapt its sail plan up and down the apparent wind range.
On a conventional boat, that would require changing the size of the mainsail by reefing up and down; on the AC75, this rapid, radical control of the mainsail is achieved by applying and reducing extreme tension at the luff; ie, the cunningham.
The ‘tiny little string’ has become a highly engineered, immensely strong component of Helix technology. It is, literally, the leading edge of sail engineering.
North Sails initially developed Helix for the luffs of downwind and reaching sails to enable sails to operate in a wide wind range, including when partially furled. But the AC75 yachts for Ineos Team UK, Luna Rossa Prada and Pirelli, and Emirates Team New Zealand demanded a much higher level of Helix development. Ken Read says it will change sail construction and sail trimming forever.
By applying extreme, high loads to the structured luff of the sail and through the sail, Helix can dramatically change the sail’s behaviour. It can even use the cunningham to control mast bend. 'Without Helix, we wouldn’t have the range that we need and it would be a much bigger compromise, either at the low end or at the high end,' says Ken Read. 'The cunningham has become the foot pedal that modifies the sail plan to do everything you need in a complicated racing yacht.'
Helix is a highly engineered carbon fibre taping system, built into the structure of the sail by robotics over a three-dimensional mould. In a complete turn-around from conventional sail-making, there is almost as much structure in the luff of the sail as in the leech.
Such technology is trickling down, fast, to a sail plan near you.
When interviewed for this article in 2021, Ken Read predicted that every sailboat, from weekend cruiser to offshore multihull, would have some form of Helix involved in its sails in the foreseeable future. 'That means people will be able to trim sails in ways we haven't seen before, and they will need to learn a few new features of sails – but the efficiency of your sail plan will change dramatically. It will reduce the number of sails you actually need.'
Thanks to development on AC75 mainsails, everyday sailors will enjoy simpler, more power sail wardrobes using technology direct from the America’s Cup.
August 29, 2024. Louis Vuitton Cup, Race Day 1. LUNA ROSSA PRADA PIRELLI TEAM, ORIENT EXPRESS RACING TEAM Photo credit: Ian Roman/America's Cup
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