America's Cup- AC72 a triple leap of faith - Luca Devoti
by Luca Devoti, Vsail.info on 30 Apr 2012
Luca Devoti has begun contributing to both http://www.farevela.net/2012/04/04/americas-cup-iniziato-il-conto-alla-rovescia-per-i-misteriosi-ac72-ac-world-series-in-rotta-su-napoli-e-venezia/!Farevela.net and FareVela, Italy’s biggest sailing media.
32nd Louis Vuitton Cup RR2. BMW Oracle Racing vs +39 BMW Oracle Racing © Photo Gilles Martin-Raget http://www.bmworacleracing.com
The Italian Olympic sailor, silver medalist in the Finn in the Sydney 2000 Olympics, skipper of +39 in the 2007 America’s Cup, founder of the Devoti Sailing boatyard that builds Finn, Melges 24 and D-One, and current coach of the Italian Sailing Federation at the Finn class, will talk about various topics related to competitive sailing, fruit of his long experience and his wide network of international contacts at all levels. A well-informed person of the facts, as well as a careful observer of what is taking place in the sport of sailing.
In this first installment, Devoti gives a critical view on the current America’s Cup and, in particular, the AC72 yacht which he considers to be an example of the 'complete lack of practicality' that, in his opinion, marks the 34th America’s Cup. Devoti has first-hand experience on the issue, having been the Sports Director of Green Comm Racing, the now defunct challenger for the 34th America’s Cup:
The problem with the AC72 wings is mainly logistical, the ability to manage and handle a piece of equipment that weighs many kilos in order to make it operate in the best way possible within the complexity of configurations that will provide the aerodynamic advantages for the best performance. All teams have positioned themselves towards a three-element wing, with three modules and a central part, the same path the Little America’s Cup had already taken.
The difficulty lies in making it work and turn, by changing its shape while using the least energy possible. We must, therefore, understand how the wing works. In the AC45 the key lies in the use of the winch that is connected to the wing and serves as sheet and runner, making the windward hull fly at an ideal height, neither too low nor too high. This is in fact obtained, especially when the wind is unstable in intensity and direction, by continuously trimming the wing in and out. On the AC45 this is done with a load that is manageable by one person with a winch, although with great difficulty. We have seen that the ideal wing trimmer is a great sailor but is also in great physical condition, especially when the wind picks up.
The load on the AC72 wing, in this sense, will be much greater, I don’t want to be wrong but I think it will be around 1,500 kg, and will, therefore, involve different sizes and approaches. We must see whether we succeed. If you remember this was the problem of the challenge of the two monsters in 2010, that is the advantage of Oracle USA 17 over Alinghi 5. Alinghi struggled to stay high and with a certain angle, it was not a problem of quality of the helmsman as much as the difficulty with a conventional sail to keep this ideal setup.
The wing has therefore only a lateral load and still very low compared to the load on the sheet, and in a conventional sail when you ease or tense the sheet, it opens, twists more or closes. This type of work, especially when made with an engine, was perfect … one got there … and inside-outside, inside-outside you trimmed. On the other hand, with a conventional sail, even with the help of an engine, it was very difficult. Therefore, perhaps, we might see wing configurations that don’t seek maximum efficiency, but maximum ease of use.
Given the race course and the venue (the windy bay of San Francisco) a lot of unknowns open up in this project. The wing is so high and in San Francisco with 25 knots of wind and steep and short waves, its dimension becomes critical. It works in theory, when the boat is at speed, because the appendices that will go on the AC72 will not be linear but curved, they will not be at a fixed angle any more but move in and out and could also change the angle of attack. The balance, therefore, is given by the dynamic lift, given by the shape of the bows and the angle of the front foil, however it is clear that if, for any reason, there is no speed, the dynamic element will be missing and the possibility to pitchpole will increase exponentially.
For the rest of this story, in English, http://www.vsail.info/2012/04/27/luca-devoti-the-ac72-is-a-triple-leap-of-faith/!click_here
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