The foil fundamentals used by Oracle in 2017 (left) and Team New Zealand (far left). On the basis that with their late start they were out of time compared to their rivals, Team NZ went aggressive from the outset. Having decided they would make the powerful cyclor system work the foil team went down the path of more open-angle wider-span foils that would be more pitch unstable but faster and with a wider performance window – very handy when your foil choice had
to be confirmed by 0800 each race day. The Kiwi control system was perfected when the team were still in Auckland, after which they worked on maximising outright speed leaving the boat-handling refinements for when they arrived in Bermuda. Late in the day Oracle also tried more open foils but lacked the hydraulic power to control them reliably
42°-angle it did not need to foil. It had enough power and VMG to win hull-borne. When Oracle were facing elimination
Jimmy Spithill took a lay day. He decided to ignore Ozanne’s advice and had the team practise upwind foiling all day. Espe- cially with their precise electro-mechanical control system, they found they could do it and it was fast. This discovery re-energised the team who went all in on upwind foil- ing, leading to their amazing comeback. In an ironic postscript Ozanne later
took another look at his software and ‘found a mistake’. It didn’t consider sailing low and fast over longer distances. Giving it another look, he found that the software confirmed the sailors’ discovery. This improvement in upwind technique
relied less on twisting the wing – whatever the superiority of TNZ’s rig off the wind, it was no longer enough to make up for Oracle’s new-found upwind advantage. Oracle staged one of the great comebacks in sport history, coming back winning nine straight to take the Cup 11-8 (Oracle had been penalised a race for improper changes to their AC45 during the America’s Cup World Series and needed to win 11 races to defend the Cup, instead of nine.)
Won aloft – 2017 Not surprisingly, Oracle’s remarkable comeback seemed to demoralise the New Zealanders for some time and interest and support at home for the next Match in 2017 was extremely slow in coming. This was exacerbated by the cancellation of Auckland’s scheduled qualifying event and the loss of its value to generate interest and resources. By the time funds did appear the 2017 Cup process had long begun and others were well along with developments. Starting late, TNZ needed a high
appetite for risk. But this time around both hull and wing shapes (but not construction or systems) were now one-design for all practical purposes. It seemed there wasn’t a needed game-changing opportunity left for TNZ… They knew that if they were to have any chance at all they had to find an advantage somewhere even if it tested the boundaries of the team’s comfort levels. They found it in the rules that required hydraulic power to be supplied only by
human effort. In their tests they quickly determined that leg/cycle grinding offered 40 per cent more power than traditional arm grinders (‘That’s four-oh’, emphasised Ashby, lest I misunderstand our conversa- tion). This led to being able to sail the boat with 100 per cent hydraulic power on tap all the time, improving ease, accuracy and speed of wing and daggerboard handling. Rather than having the helmsman fly the
boat, with hands no longer needed on the pumps the ever inventive Kiwis could make a crewmember responsible for flight control, enabling the helmsman to focus solely in two dimensions on speed and tactics. As viewing the Cup races showed, in
comparison Oracle were regularly starved for power, with the helmsman more dis- tracted as he worked to control height as well as speed and course management. The cycling had a further quantifiable
windage advantage. When their competi- tors needed maximum power, grinding had to be done from a standing position. In wind tunnel tests by TNZ it was determined that the lower-windage drag of the cyclists, practically hidden from the boat’s 30kt+ apparent winds, gave TNZ an eight-second advantage over the length of a course vs standing grinders. At AC50 speeds that’s about a 125m gain at the finish, a veritable horizon job. The advantage was far less against kneeling grinders, but power output from a kneeling position is far less than standing so very probably more seconds were lost due to this further power deficit. Aside from cycle power the foil systems
were key elements in 2017; most of the investment of the teams went towards foil design and function. TNZ also did a better job of designing their foils which appeared to have a much wider range of top speed. As Glenn Ashby described, TNZ concen- trated on maximising effective span, which gave their foils the wider performance window evident in the Cup Match. This greater effective span resulted from
foils with a more ‘open’ angle than the others. The more open-angled a foil is the more pitch unstable it is. But Team New Zealand, with 100 per cent power avail- able from the cyclists at all times, were better able to perform in the face of this increased instability.
A new twist One of the great attributes of advanced composite structures is so-called aerialistic tailoring, where structures, especially thin wing-like structures, can be made to bend advantageously in directions opposite to what might be expected. This is accom- plished by discrete unidirectional layer placement. For instance, where a homoge- neous material like aluminium might bend or twist in adverse fashion as it loads up, a properly designed composite structure can be designed to bend or twist less under load. A good example were the T-foils on the
AC50 rudders. These foils increased right- ing moment if angled negatively on the windward side. But rules limited rudder T-foil angle differences to 3°, port to star- board. But the composite engineers created designs where the windward T-foils increased in negative angle as the boats powered up, increasing righting moment. One of the reasons Oracle had seemed
TNZ’s equal before the Cup was that they had removed the lower pair of shrouds, allowing the two hulls to rack much more relative to each other, effectively increasing the weather rudder T-foil’s negative angle to gain righting moment. By the time the America’s Cup Match began, though, TNZ were on to Oracle’s idea and they mimicked it, nullifying their advantage. Once again the Cup was won by care-
fully calculated risk and well-developed solutions. This time, with the cyclists and the decision to relieve the helmsman of control responsibilities, TNZ made up for their very late start, ultimately winning the America’s Cup by historic margins. The new Defenders have chosen a foil-
ing monohull as the new America’s Cup Class. It comes with a soft rig similar to the early 2010 rigs with wing-shaped mast and mainsail combined with headsails. With more crewmembers actually sailing the boats, the visual excitement of crew work is sure to bring more interest and excitement back to the event. Will history once again deliver examples
of the same kind of courageous, difference- making decisions so typical of America’s Cup winners through the years? Almost certainly… I can’t wait for the next one. q
SEAHORSE 45
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