Leading edge development in downwind sail design

Doyle Sails’ CEO Mike Sanderson has figured out how to apply Structured Luff technology to gennakers – and the (racing) result speaks for itself…

Technology generally progresses not in a smooth upward gradient but in sudden bursts of inspiration followed by periods of more linear refinement and development. One such burst took place when Doyle Sails introduced its new Structured Luff Downwind sail at the Sorrento IMA Maxi European Championship in May.

Hap Fauth’s former Maxi 72 Bella Mente won the event with a race to spare sporting one of the new sails, which drew plenty of attention on the race track and much dockside discussion.

It is the brainchild of Doyle Sails CEO Mike Sanderson, who identified that the recent turbo-charging of the former Maxi 72 class had opened a gap in the inventory. Some of the boats have been lengthened and several, including Bella Mente, have added twin rudders and water ballast.

‘As the 72s have got lighter and more powerful, they have become significantly faster than they were 10 years ago,’ Sanderson notes. ‘We are now often sailing downwind at apparent wind angles of 50-55 degrees. To expect nylon or polyester spinnaker material to cope with a jib-like angle of attack is a big ask.

‘I had been scratching my head trying to figure out how to transition into a narrower apparent wind type of sail without losing the conventional abilities to do string drops, peels, standard gybes, regular packing and so on.’

Eventually, Sanderson produced a sketch showing a Structured Luff-type lens on the leading edge morphing into a more conventional soft sail towards the trailing edge. ‘I put the concept to our designers, but initially I got no traction at all. It was like I had fallen out of a tree on Mars,’ he laughs.

Above: Mike Sanderson sketched the concept, then a prototype was designed, built and tested on his own yacht.
Below: the next step was to scale it right up to maxi size on Bella Mente

Then, Justin Ferris and Andrew Lechte started to play around with the concept and produced a prototype for Sanderson’s own 35ft Rob Shaw-designed canting keeler. ‘We tried out the new sail with my son, Merrick, filming it on his drone. I circulated the video footage to the designers and told them, “This idea has got legs, guys; we need to start paying attention.”’

‘Richard Bouzaid, who is a genius with this kind of challenge, managed to get the concept to run on our software and from there we were able to engineer the structural transition from Stratis material down the forward section to off-the-shelf polyester. To be honest, the result has exceeded expectations.’

Sanderson confesses that the first time they hoisted the sail on Bella Mente, it was one of those moments when you close your eyes and then slowly take a peep to see if it is surviving. ‘It is one thing to try the concept with the family out on a 35-footer,’ he says. ‘It is another thing altogether on a maxi where the loads are totally different. But it worked straight out of the bag.’

Before the Sorrento regatta, the Bella Mente crew assembled in Palma for a week’s training, where the sail had a good workout. ‘We tested it thoroughly for performance and reliability. We had it up in sloppy seas and smooth water. We explored how it performed in reaching conditions and running quite deep angles. We practised gybes, string drops and peels.

‘By the time we got to the regatta, the sail had already accumulated quite a mileage but it went straight into our frontline racing inventory. We used it every day of the regatta except for one day of windy windward-leewards where it was out of range.’

In race mode the sail proved extremely flexible with a wide performance sweet spot. Typical maxi racing situations involve passages between and around islands, often demanding apparent wind angle changes from 50 to 80 degrees. ‘Those are big shifts from a load standpoint,’ says Sanderson.

‘In highly competitive fleets, we also need to allow for frequent tactical moves, defending or attacking high or low. With conventional laminate sails of this type, the performance window is very narrow. If you have to put the bow down for tactical reasons, the performance just falls off a cliff.

‘With this new Structured Luff downwind sail the potential is huge, we found it was possibly faster in every respect. We improved on the performance of a conventional sail in its target range, but were able to put the bow up or down and still feel like we had a speed edge. That is a very big deal for us in the type of racing we are doing.’

Although the Bella Mente sail was built to a light wind A1-type configuration, its stronger construction and the ability to project forward in a typical Structured Luff lens shape allows it to handle reaching angles further up the conventional wind range. It stood out, both literally and figuratively.

‘It definitely drew a lot of attention,’ says Sanderson. ‘People were talking about it. We had other teams putting in orders in time for the September Rolex Maxi Worlds in Sardinia. ‘One team ordered three of the new sails.’

‘We are still in the early days of refinement but this concept has already exceeded our expectations on all points of sail, so that is pretty satisfying,’ he adds. ‘Our designers did an amazing job of turning the concept into reality.’

Sanderson also paid tribute to Hap Fauth’s willingness to try new things. ‘We sometimes call the boat Experimente, Sanderson laughs. ‘We have had a fair share of wins and the odd loss, but we have an owner who just loves pushing the boundaries and thinking outside of the box. He doesn’t want us just sitting still.

‘Apart from the experimental sail on my 35-footer, this version of the Structured Luff Downwind Sail was really Mk 1. I was impressed and proud that it worked so well on its first competitive outing. But we are pretty confident there is more to come. Watch this space.’

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