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      Abbreviated rules   07/28/2017

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Nodrog

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  1. Race 2 similar, ORUSA seems to be the faster boat, or certainly no slower Polars this time in 10knts avg yTWS, they sailed in pretty much the same pressure in all of Race 2
  2. Got the VMGs right I think, below showing only VMGs in average 9knots yTWS. USA had edge upwind, NZL downwind. This Race 1 only
  3. Polars on the data thread, ETNZ sailed in more pressure in Race 1. Comparing only when boats were in average of 9 knots USA had better upwind VMG, NZL better downwind.
  4. Am struggling with my not so nice Excel polars, something wrong with the calibration on yTWA I think, but it does seem ORUSa had better VMG upwind. Hopefully Dorox can confirm. The big difference, in Race 1, was NZ sailed in more pressure more often
  5. Team NZ

    Interesting, I thought I'd check the data files, as there is a yRudder field reported. In the challenger series ETNZ recorded this, at first glance mid tack its equal ( either +20 or -20 roughly) regardless of which way they tack, so they either didn't have Ackerman then, or yRudder records and averages the angle of both rudders. In the AC finals, the yRudder field is zero in all the ETNZ data files, perhaps the sensor 'stopped working' on ETNZ !! The USA one kept working.... I'm sure a close look of a video through a tack / gybe would tell us?
  6. Parade Route

    5 days with tiki would.be good though
  7. Dorox, your data was quoted on a Facebook feed I saw. Some insightful words I thought, essentially I think ETNZ have traded more drag on reaches for more righting moment, and hence higher VMG, upwind https://www.facebook.com/Ellway-Aero-Hydrodynamic-Designs-671685749655101/ Musings from the Americas Cup – why ENZ won the LV to become challenger. The AC has provided some great racing and spectacles. Here are just a few thoughts on possible reasons why ENZ went through to face Oracle. The attached upwind polars of ENZ v Artemis (from Sailing Anarchy) show superior all-round performance of ENZ, especially in lighter winds. ENZ flight control There has been much discussion on whether bikes provide greater power output or more or less windage. The biggest advantage (by far) is that by using bikes, the cyclor’s hands are free to do other tasks. The most important of which is flight control. Those of you who kitefoil or windfoil know just how many minute control inputs via your CofG are required to keep at the correct pitch and height above the water. In an AC boat, this control is made by altering the AOA of the front foil. On BAR for example, the control function was left to the helm. But on ENZ it is the task of the 3rd member from the stern. He is playing a ‘computer game’ matching his control output to an ‘artificial horizon’. This allows far more rapid control of the foil and much tighter control. In turn, this has allowed the boat to be flown higher out of the water (so less shaft drag), and to maintain better control in manoeuvres (especially tacks), when large control movements are needed to compensate for the rapid changes in speed and thrust. ENZ hydraulic wing control Unlike the other challengers, the wing trim appears to be hydraulically controlled rather than using a sheet via a winch. It appears that this allows more rapid and accurate wing trim in order to control the boat’s heel. In turn, this has allowed the boat to be sailed with an amount of windward heel. Windward heel increases righting moment and thus speed once fully powered. ENZ foils The foils clearly have large spans. Induced drag (the drag produced as a direct consequence of producing lift) dominates at lower foiling speeds and is a function of effective span^2. So this larger span, if coupled with a suitably small overall foil area, is probably what contributes to the large wind range of the ‘all round’ foils that ENZ most often use. The foils also appear to have larger taper ratios (tip chord/root chord) and a lot of washout out (trailing edge up twist) towards the tips. This creates a foil which will behave a bit like a twisted sail. At high AoAs the tips will contribute to lift, but a lower AOAs the tips may produce no lift, or even negative lift (push down). The effect of this is to move the centre of pressure (CoP) progressively outboard towards the shaft as the AOA is reduced. This has 2 benefits: The bending loads on the foil are reduced allowing for a thinner, lower drag foil sections towards the root. Also, as speed increases and the AoA of the foil is reduced, the CoP moves outboard increasing the boat’s righting moment. This foil design will create more induced drag than an elliptically loaded foil of the same span. At higher speeds, it will also create more drag because of the parasitic drag of the tips. I think we saw this latter effect downwind when Artemis (on small foils) was faster on leg1. But overall, these factors may explain the exceptional all-round performance of the foils. ENZ v Artmeis – final day. The winds were light, but increased. Artemis was on its large, light wind foils. ENZ on its all-round foils. Artemis appeared able to foil and sustain flight at lower speeds (around 15kts) than ENZ. This suggests that the Artemis foils were of larger overall area, camber and thickness. As soon as the wind increased, this rendered Artemis uncompetitive. But even in the light winds, Artemis appeared to gain no advantage. One possible reason for this is that in vmg terms, it is only faster to foil if the foil offers a better L/D ratio than the displacement hull. For the 50ft AC hulls, I would expect the optimum min drag speed (speed above which flight can be maintained) to be around 18kts. If Artemis was flying at significantly lower speeds, then this would suggest that its foils were unnecessarily large – it would have been better to use smaller/thinner/less cambered foils, foil a bit later, and sail high in displacement mode for longer (e.g. like ENZ).
  8. Absolutely would, but I can only get so much out of Excel! The issue I have is the data is really noisy, and is delivered at differing frequencies, so polars end up with a lot of scattered dots, not the firm 'target line' that we'd like to see. I don't have the resource to get a firm 'target' boat speed ( i think a 95th percentile?) at every yTWA and yTWS combination. Drawing a line around the maximum ever achieved at each TWS/TWA combo I don't think gives realistic numbers, that would just be a record of all the errors the instruments have logged during racing. If someone has access to R / matlab / SQL / real computing.... then a matrix of TWA and TWS, averaged over say 5 seconds (?), with the mean / median / Std Dev in each 'box' would probably help? But not sure the boats are sailing in a steady state long enough for us to get decent averages? I've taken the approach that VMG is what matters, regardless of the TWA to achieve it, so try to show the highest consistently achieved VMG at different wind speeds.
  9. Today, in 11 knots of breeze [yTWS, averaged over 3 seconds], orange line, they were consistent in getting 16.5 to 17knts of VMG. The peaks here to the right, as supposed to the longer distributions seen prior indicates to me they were sailing in their groove alot of the time, maxing VMG, rather than a wider range we've seen before. I've a file of all the NZL data from the Qualifiers, when they had a variety of set ups, and 15.5 to 16knt VMGs were pretty good [ edit: in 11knts yTWS, averaged] but for many of those they would have been sailing in a lull with a heavier air set-up. 17's were still achieved, and much higher through tacks etc. Need to find a data file for when they had a similar set up to today.
  10. Dorox, fantastic work, knew someone would be able to do a proper job of it. Am hoping to have a chance today to compare ETNZ's VMGs vs similar wind speeds earlier in the comp. Pretty sure we're going to see a significant improvement. Can someone remind me which data set day had ETNZ with the big bat foils in around 10knts?
  11. Team NZ

    PL said something similar on the Vodafone 'dock out' show thingy which is on facebook, or is it the same broadcast as Radio Sport? Very cagey, but they've something up their sleeve, he believes...
  12. Team NZ

    I think there might have been a problem with the front cyclor in one of the races, when they showed a resting heart rate it looked like he was reaching forward under the deck to adjust something that wasn't co-operating, and there was a shot of him turning around and encouraging the guy behind to keep on giving it heaps, which he clearly was.
  13. Team NZ

    ^ word The video interview was well balanced and insightful, and remarkably frank. . The article was shite.
  14. Another way of looking at things, does this chart make sense? I'm wanting to show tactically how well a race has gone. The example here is ETNZ when they sailed USA in RR2. The x-axis shows the difference between the TWD measured by the yacht, yTWD, and 'course wind' (same throughout the race). Strictly speaking the bar labelled '1' is all the datapoints between >=0 and <2 Degrees, mid point "1". Not sure if this is exactly the same as the direction from middle of bottom gate to top gate, is 'course axis', but don't think it matters. Angles to the right are when the yacht is upwind, on a lift. Red bars for port tack lifts, Green for Stbd. The further from the centreline the bigger the lift / knock. The taller the bar the longer the boat was in the lift / knock. If this makes sense can repeat for USA in same race, and then Semis etc....
  15. Team NZ

    Not sure if I'm late on this comment? Hugh Wellbourn's comments re the tip being the result of PB sailing in the turbulence of BAR's foil wake. Not alot of arial footage I can find, but in this they look to be still to w/w of the wake when they tipped it in, or should I say 'had a bit of bow down trim' - classic quote !!