Above: 2014 International Moth World’s runner-up Chris Rashley racing in January in Australia on his Kevin Ellway-designed Exocet Moth. In 2014 at Hayling Island Rashley won an impressive 5 races. The big problem with foil solutions to date on twin-hulled platforms is long period cyclic porpoising, seen here (left) on Team New Zealand’s AC72 in 2013. It was the overnight manner in which Oracle began to get on top of this behaviour that led to their jump in competitiveness… as well as to widespread claims that the American team had introduced a money-no-object aerospace control solution
– Part1
Australia’s 49er Olympic champion sailed an exemplary final day to take his second world title, Rashley’s second overall demonstrated Exocet’s potential. With a three-year waiting list for a new Exocet, and a number of top sailors such as Rob Greenhalgh, Chris Draper and Paul Goodison shifting over to the Exocet and finding improved performance, this has become the most desirable Moth on the market.
Ellway himself loves to sail – and race – his own Exocet out of his home club on the Solent, Stokes Bay Sailing Club, not so very far from where the first America’s Cup World Series takes place in Portsmouth this month. But for Ellway and the foiler Moth it was definitely not a case of love at first sight.
‘My first go in a Moth was in 2009, and the build quality of the example I had was substandard. The design is not really differ- ent from what it is now, but there were problems with the wand that drove the flap. ‘Sailing at a choppy water venue like Stokes Bay was impossible. For sailing in
anything other than flat water, the thing used to just try and kill me every time you went out. You’d be sailing along, and for no reason it would leap out of the water and throw me onto the shrouds. After cracking my ribs on both sides I just about got to the point where I had had enough of this. And then I eventually discovered that there was actually something wrong in the way the boat had been assembled, and sorted it out.’
With a professional background in engi- neering, Ellway has never been a fan of the ‘trial and error’ process of developing tech- nology. He prefers to use mathematical modelling to run the numbers, and he was intrigued by a VPP model that had been posted on the Moth class forum in 2009. The author was Alan Smith from Aus- tralia, and Ellway was sufficiently intrigued to make contact with Smith. They have been working closely together ever since, although solely on email. They have never met, indeed had never even spoken until they came together for a Skype interview for this article. But in terms of their general outlook and philosophy, they are bosom buddies, both fans of doing as much of the trial and error as possible on the computer, rather than on the water.
‘I’ve been fiddling with mathematical modelling of sailing yachts for a long time,’ says Smith, now 80 but still too young to take up crossword puzzles, he claims. ‘The original study I did was in 1966 but I was aware as early as 1960 that it was possible to foil a sailing yacht. You couldn’t build one at that time because available materials were simply too heavy, but progressively better materials came online and in 1999 I worked with David Lugg to get his International 14 up on foils. But the 14 class promptly banned having two foils so the project was dropped. ‘At the same time the Moth boys in
western Australia, particularly Brett Burvill, were experimenting with foils. So I started applying the techniques that I knew were applicable to aircraft design to Moth designs. I couldn’t get anyone here in Aus- tralia to take an interest in the scientist’s approach to the design work, and when I put that very simple velocity prediction program up on the International Moth website Kevin was the only person to respond… and we’ve been working together ever since.’
Smith estimates that he has put more than 5,000 hours into his modelling work in the past six years with Ellway, who has put in even more time. ‘When I first con- tacted Alan I had already designed the Ninja Moth which went on to win National and European titles. That boat had a number of innovations that have since been adopted as the norm. ‘Prior to the Ninja, Moths used to have rear foils of similar area to the main foil. Drag and simple stability analysis indi- cated that this was far from optimum so we tried a much smaller high-aspect rear foil.’ Reducing the chord width of the vertical struts and foils has been another development that Ellway says has since been adopted throughout the fleet, another means of reducing wetted surface area. ‘Alan and I have reviewed, considered and analysed just about everything you could possibly think of on the Moth, from optimum foil and hull shapes to hull and sail aerodynamics.’ Among many resulting improvements have been the reduction of wetted area, increase in span and stability improvements.
Mathematical modelling of the dynam- ics (ie mathematical simulation of the boat’s motion) has proved invaluable, says Ellway. ‘You can’t sail fast unless you have control. Moth sailing is more than just about sorting out speed in static terms, it’s
SEAHORSE 37
THIERRY MARTINEZ
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