Once the AC50 was confirmed (and they had some coin) ETNZ made the collective decision to go for the fastest possible foils first and work out how to control them second. That drove the development of a control system very different from their rivals – different and superior. Systems engineering lay at the heart of this success. Others tried aggressive foils but gave up on them; that one early call removed the option of backing off, forcing the Cup winners to press on with a speed-first strategy – however crazy it felt at times
foils with which we won the America’s Cup – we called them seven and eight – were considerably different from the test foils. That showed confidence in our tools, because those would become one of only two pairs of race foils. To commit to those, even though they were quite different from anything we had sailed with on the water, did require a level of confidence in our simu- lation that they would be sailable and fast. ‘How we got there was a process of
multiple iterations. For the five test foils and four race foils we had on the water we must have done laps on the simulator of at least 500 test foils and 400 race foils. That is the beauty of simulation. It takes only five minutes to try a new shape.’ With the sailors driving the simulators,
they could also contribute ideas about foils that could be quickly run through the program. ‘As designers we were lucky to have the sailors we did have. They were all equally committed to pushing the process as hard as possible. We did run tests on some shapes that were completely uncon- trollable, but in the end we arrived at foils that had very little compromise in perfor- mance and were controllable.’ The end result was the sharply angular
foil shapes quite different from the rest of the fleet’s – and reckoned to have about 20 per cent less surface area than Oracle’s race foils. This area reduction was achieved by using higher aspect ratio foils with shorter chord lengths – something Oracle tried to move towards by modifying their foils in
40 SEAHORSE
the five-day break between the first and second Match weekends. Having opted for very high-performance
foils, the next challenge was getting the most out of them on the water. Here the design team came up with a fully auto- mated test system where computers flew the boat on an autopilot they named Polo. ‘This was useful to prove where we could get to with control of the foils, to set the bar if you like. The sailors could see what the computer could achieve and challenge themselves to match it.’ And to a large extent they did. ‘Through
the manoeuvres the sailors could actually do a better job, but in a straight line the computers had a slight advantage. They have a higher control bandwidth than humans, which gives them more instanta- neous reactions.’ For racing, of course, automated systems were outlawed, so the team had to develop manual control sys- tems and techniques to replicate the auto- mated performance as closely as possible. Important as the foils and their control
systems were, they were only one brick in the wall and the task for the team was to integrate all the elements into a coherent package. The hydraulic wing control system and the chosen method of trimming for twist played a significant role, as did rudders and elevators, which represented a late part of the ETNZ development. A lot of work went into making the most
of the permitted 3° rudder rake differential which enables the windward rudder to
exert considerable downforce, adding to the righting moment of the boat. On arriv- ing in Bermuda, ETNZ spotted that Oracle were sailing with slack lower shrouds and soon realised that this would allow the hulls and platform to twist more under load, dropping the windward bow and consequently increasing the windward rud- der rake by as much as 0.5° – enough for a significant increase in righting moment. Reconnaissance photos of the Oracle
boat confirmed this increased ‘racking’, and a war of words between the teams and the measurers ensued: a rule interpretation initially stated that sailing with slack lowers was not permitted, but this decision was later reversed. Now ETNZ would have to match Oracle to remain competitive. ‘We then needed to strengthen our wing-
spar to allow us to sail without the support of the lowers, and had planned to start by reinforcing the spare wing,’ explained Bernasconi. ‘Then we capsized, and sud- denly we needed that spare wing on the water, delaying the modification pro- gramme. In the end we first sailed with the reinforced wing and slack lowers only the day before the Match – and were learning about the limits from then on.’ The race rudders, like the foils, were
quite extreme, very low drag with elevators that could twist under load. ‘The elevators are highly loaded areas. If you can design appendages to deform under load in the direction you want them to move there is performance potential to be found.
w
INGRID ABERY
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80 |
Page 81 |
Page 82 |
Page 83 |
Page 84 |
Page 85 |
Page 86 |
Page 87 |
Page 88
