Left/above: when it wasn’t a case of drifting around, the 2015 Moth Worlds were very much a full-on affair. Numerous sailors struggled when the breeze – and sea – was up, with a clear distinction opening up on the windiest days between the top couple of dozen Moth ‘artistes’ in the gold fleet and the rest. It was all meat and drink to Pete Burling (right) who was unstoppable – especially off the wind
anhedrals are quite unstable. The dihedral is the most stable.
‘Fighter planes where the wings are angled downwards turn really quickly. Planes where the wings are angled up find their own balance. So the thing about an anhedral foil is that it’s inherently unstable and tries to capsize the boat. There’s no stability, in fact there’s instability, and if you can get it to try to capsize the boat to windward then it increases your righting moment. You’re trying to get the foil to throw the boat on top of you. If it wants to capsize you to windward, then it’s adding to righting moment.’
Above the water most of the front - runners are now using canting rigs, with the mast canting away to leeward to bring the sailplan more upright while keeping the boat leaning to windward (which again increases righting moment). This was an area where Burling drew on the resources of Emirates Team New Zealand to really get his canting mechanism working smoothly. Burling was good enough upwind, but downwind was the fastest of the 165-boat fleet in just about all conditions. ‘Yeah, good wheels downwind, and pretty good to windward. Tommy [Slingsby] was quick upwind, and Nathan too.’ Burling says he weighed about 82kg for the championships, which he reckons to be similar to the other podium finishers, Outteridge and 2012 World Champion Josh McKnight. Top European finishers were Chris Rashley and Chris Draper in fourth and fifth respectively, both weigh- ing a bit less than 80kg. Tom Slingsby was considered the fastest upwind in good breeze, whom Burling reckons to be weighing in somewhere just shy of 90kg. The Mach 2 has now won the past seven Moth world titles which, by Simon Payne’s estimation, makes it the most suc- cessful design in Moth history. The British- designed Exocet has been threatening the
Mach 2’s dominance for some time; however, the lead time for delivery now stretches out to a couple of years. There were only three Exocets in Sorrento, of which two were sailed by the Brits to fourth and fifth overall. The Exo- cet was designed by Kevin Ellway and is built by Simon Maguire. Ellway worked very closely with Rashley in the build-up to the past two world championships, and also with sail designer Mike Lennon, in his own right a world-class Moth sailor. Ellway offers these observations on the Sorrento worlds. ‘It was a very short time interval between Hayling and Sorrento, so there was little opportunity to make signif- icant performance gains.
‘With limited time, it was important to look at the factors that have the biggest effect first. The CFD analysis we’ve done suggests that the biggest gains can be made from improvements in sail design, both upwind and down. The aero fairings, for example, that have been so prevalent in the class for the past couple of years, are really just tinkering around the edges.’ Burling agrees with this point. ‘Some of the fair- ings look nice, but they can start looking ragged pretty quickly with all the hard crashing that the boat takes. I don’t think they’re worth the time or the bother.’ Ellway continues: ‘The other massive factor (literally) is body weight and height. In anything over about 10kt VPP analysis shows that you just can’t be too heavy and tall. Unlike on conventional boats, foil drag is almost independent of weight when sail- ing at speed. The windage (another major drag factor in the Moth) is about the same no matter whether you’re big or small, so being tall and heavy is the way to go in what was expected to be a windy venue. In flat water, in anything over 9-10kt of wind a 90kg sailor has about a 0.4kt upwind speed advantage over a 75kg sailor – with no disadvantage offwind either.’
Ellway says the collaboration with Chris Rashley and Mike Lennon is begin- ning to pay dividends. ‘We have been working as a team since before Hayling. I have done a lot of aero work, and design- ing the mould shapes of the sails. Mike has been applying his skills to produce a practical sail. Rashers [Rashley] has been supplying detailed sailor feedback and photos for shape analysis. The AX1, as used by Rashers to finish second in the 2014 worlds, was our first effort, but we knew we weren’t really achieving the fly- ing shapes to match the CFD optimums. ‘Mike has since developed a really good and very light membrane lay-up. For Rashers we decided to switch from XPly (as used by KA and North) to this more stable material. A few prototypes later and we knew we were getting somewhere. Not long before the worlds Chris Draper contacted me and asked me to design a sail to suit high winds and his light weight (around 76kg). For this we stuck with XPly, which has the benefit of uniform stretch characteristics. The Rashley and Draper sails have similar flying shapes, but the mould shapes differ to account for the differences in material stretch.’ Payne says there is a growing trend to lower the rig in the boat, something that first appeared at Hayling last year. ‘By dropping the rig it effectively makes you “heavier” through a reduction in heeling moment,’ says the double world cham- pion. ‘So if you are fairly lightweight that’s a pretty good thing to do.
‘Importantly, there doesn’t seem to be any light wind penalty for doing this, and you might see this being more widely adopted. But you still need to get under the boom, so you are starting to see concave booms that have the added effect of being able to use the outhaul more freely. But most importantly the sailor can get under the boom with the lower rig plan.’
SEAHORSE 41
THIERRY MARTINEZ/SANDER VAN DER BORCH
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