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      Abbreviated rules   07/28/2017

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dachopper

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About dachopper

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  1. The top guys aren't moving their kites going to windward , they are as low as possible, but downwind different story. If the rider feels comfortable they increase apparent wind to go faster
  2. I can't help but wonder, ...... The kite foils that guys are now riding, and the Race kites would decimate that thing Bryan rode against the ac72 5 years ago..... Which is why no0one competes with tube kites on race circuits any more = guaranteed loss. 17 / 18kts upwind VMG in 5 - 6 kts........ I don't think the AC72 would stand a chance until the wind was cranking..... actually after checking, it appears that 17/ 18kts is the VMG max upwind displayed on the AC72 polars, in 20 + kts
  3. So its a 75 foot version of the quant 23 https://www.2luxury2.com/european-yacht-of-the-year-2016-winners-prizegiving-at-boot-dusseldorf/quant-23-kielboot/
  4. Here is another thought.... On Kite foilers, the foils are effectively fixed AoA before getting into the water. Balance is achieved through weight distribution fore and aft, in response to how the foil was setup in the first place, but the weight distribution is just changing the Angle of incidence and Rake of the entire underwater getup as one piece to achieve longitudinal stability. It would be easier I would have thought, to engineer either a single piece pivot foil, or split piece limited movement pivot foil. A hinge inside the Main foil mast near the Leading edge, and internal torque tube near the aft edge. The Lift / AoA curves of most of the foils lend themselves to numbers like a 5 degree change in angle of attack = 300% change in the amount of lift. So we are only talking small movements required to achieve stability over a massive speed range.... like 10 kt ( Two foils required ) , 20kts - 1 foil required at 5 AoA, 60 kts 1 foil required at 0 AoA. These same foils also have negligable change in Drag Coefficient in their design AoA brackets. The other issue is Extremely basic, but weight movement to balance the pull of the kite, is minimized as the riders arms are moving in and out, but effectively holding an amount of pressure - which directly relates to kite lift. As gust hits, line tensions and bar moves out when arms are pulling at a certain pressure, that minimizes the board response needed for the abrupt changes in wind strength or direction - Board position changes in that respect are mainly to increase or decrease the ballast position in or out through lean angle + stance distance to foil, and again they are pretty small in size. Maybe some kind of pressure trimming feedback mechanism / winches that hold line pressure set by the trimmer would be the simplest interpretation.
  5. The author seems to be talking about the case where wind changes are going to heel the boat more? or push it sideways more, and the comment about higher speeds downwind seems to be a different issue. My 2 Cents is that a single foil needs to be trimmed to generate the target lift at target max speed. That way before the max speed either longitudinal Angle of attack, OR features like flaps or deploying 2 foils at once are able to boost the low wind AoA until they are retracted. Then you won't end up stuck at an uncontrollable elevator at max speed
  6. I was just looking at the picture wondering the same thing, Move the pivot up near the deck , now you have much less of a problem of lever arm, because it has the room to move a lot more into the hull, and outside the hull - which means it can be longer if needed due loads. Don't know why you would need winglets..... you have a large enough rudder + Main foil mast section to provide lateral resistance, and to resist roll from each other. Can't really see the big picture of why you would add winglets?
  7. On a Micro scale apples and oranges, On a macro scale not so much. Both are designed to ride on their hydrofoils and not on their hulls, and are wind powered. 1 uses crew weight, the other one probably won't, but will use something else instead Since there are no rules set.... and they said they would change the rules to make it work. Who is to say it will be 7 tonne, ' classic rigged ' , that they will stick with soft sails if they aren't going to work, or if they are going to use conventional or wing sails at all. They did set out their goal, and said they would alter the design to achieve it. Two different designs for sure, both using the same principles of motion.
  8. I think a few people are going to be shocked with what can happen. I know on the kite foilers in 5 to 6 kts wind speed, they are logging 25kts speed, with 17-18 kts VMG upwind In 5 to 6 kts
  9. So look at that picture, Split the Hull in half down the middle so that now you have maybe 30% more Hull surface area, then add 2 x massive cross beams ( One front and one rear ) and netting to go with it. Part of the drag equation involves skin friction, and interference drag. Those cross beams look to have more cross sectional area than the hulls, and behind them you have a flat trampoline, so part of the equation involves almost cat 4 x hulls worth of cross sectional frontage + the worlds best drag inducer in the middle. Netting.
  10. Unless you think the ' NEW' AC 50 is going to be doing 200 kts, then flaps are not going to do a thing except give the Cat design even more drag.
  11. External lever it is then
  12. You can optimize a Cat for aero all you like, there is always going to be more of it, than there is of a mono = more drag. I think there are a bunch of foils out there now that provide supercavitation, and reasonable performance with sub cavitation / takeoff mode. The issue is at higher angles of attack - 4 - 7 degrees, these foils have multiple times the co-efficient of drag than traditional foils. until the AoA is back down There will be a crossover point.... question is, will the boat get there under wind power? Could they inject air onto the leading edge to force the foil to be cupercavitating at high speed like some other new marine designs
  13. I would imagine start with the 1.2 to 1.5 tonne high speed foil, then "add" / integrate the components to allow slower speeds. Like the aero design of the Pagani Haura, I'm sure they went for the shape first, then added the active aero / drag reducers after.
  14. Hypothetically....... You could have some mechanism on the foil, that changed it's characteristics such as: some kind of trailing edge flap that deployed ( mechanical ) A. Which would allow the higher speeds with minimal drag penalty before use followed by a large increase to convert speed into extra lift / drag, and then large drag reduction once hull is out and flap is pulled back in B. Fit a flexible membrane over the top surface ( like rubber or something ) and just inflate to increase camber at takeoff speeds. They both sound crazy, but we are talking Americas cup, so whoever figures out how to accelerate until foiling https://www.youtube.com/watch?v=RU78lAJRIsQ
  15. Hypothetically....... You could have some mechanism on the foil, that changed it's characteristics such as: