AC 36 Foiling Monohulls

Discussion in 'Sailboats' started by OzFred, Sep 13, 2017.

  1. Doug Lord
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    Doug Lord Flight Ready

    You need to practice reading: he clearly and specifically addresses recreational sailors saying that foils are dangerous and then illustrating that comment with the absurd comment of coming off the foils at 40 knots. An uninformed and unfortunate comment if there ever was one!
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    After the completely off the wall comments by JB Turner, the Quant 23 was a relevant example of what some recreational sailors can sail and the speeds they are likely to achieve when sailing it. Further, it clearly illustrates that there is a lot more to foiling for recreational sailors including flying some boats in the lightest winds and sailing on foils very comfortably with virtually no danger at all.
     
    Last edited: Apr 13, 2019
  2. Doug Lord
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    Doug Lord Flight Ready

  3. CT 249
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    CT 249 Senior Member

    It's great to have you here. Many of us have had issues with Doug because of things like his insults and endless re-posting of self-promotional posts and those that are arguably presenting a one-eyed view of design. None of those issues apply to you.

    In this case, for example, you didn't insult JB Turner's comments. Doug did. Why should we let that pass? Why is it wrong to ask Doug for the reason he feels that he has the right to call someone else's comments "absurd....uninformed and unfortunate...nonsense"?

    If someone insults someone like that and then makes a statement about helmet use, why can't we ask him about his background so that we can assess whether the statement is based on experience or not? I NEVER made any comment about your helmet use; that's a reasoned personal choice and you have the experience to make it. I was merely asking Doug whether he also had the relevant experience.

    Please note that nothing I said about Doug was as insulting as the remarks he made about JB Turner. Surely you would not expect BDF to have a double standard that allows Doug to insult the views of other people, but doesn't allow us to ask Doug polite (if pointed) questions?

    The bottom line is that some of us will treat Doug as he treats others, although much more politely. If he doesn't like copping pointed questions then he should stop abusing other people.
     
    Last edited: Apr 13, 2019
  4. tspeer
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    tspeer Senior Member

    Actually, canting the rig by itself does not have much of an effect on heeling moment. There is zero effect if the side force is applied at the base of the rig. What is often missed is the need to displace the rig to leeward (or to windward if canting to leeward). The Sailrocket rig is displaced a long ways to leeward. This makes canting effective because it gives the vertical force component a large lever arm.

    The other way to look at it is to consider the distance between the net aerodynamic force vector, which is approximately right angles to the rig and taken at the center of effort, to the center of gravity. If you rotate the rig about the center of gravity, there is no change to the distance and no change to the heeling moment. But when the rig is to leeward, you can rotate it so that the force vector passes through the center of gravity and there is no heeling moment at all. The Sailrocket geometry is arranged so that the force vector from the rig and the force vector from the main foil are practically colinear. This could not happen if the rig was directly above the main foil.
     
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  5. tspeer
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    tspeer Senior Member

    Landyachts and iceboats cant their rigs to leeward to reduce heeling moment. It is effective because their vertical force is created well to leeward. If the force from the rig were to pass through the leeward wheel/runner, there would be no heeling moment at all. Of course, it isn't necessary, or even desirable, to go to that extreme. They only need enough reduction in heeling moment to ensure that heeling and skidding happen at about the same time. Any less heeling moment and the yacht will skid under the sideforce. Landyachts also benefit from the downward aerodynamic force of canting to leeward because it helps to keep the tires from skidding.

    Heeling a Moth to windward works because it makes better use of the foil, and because the center of gravity is a long way to weather. Side force on the strut results in asymmetric loading of the foil, reducing the effective span, and increasing the drag. Heeling to windward generates a vertical force component that unloads the foil, which reduces the drag. There's an aerodynamic benefit as long as the decrease in drag is more than the loss of the horizontal force component from canting.

    The AC75 is different. The center of gravity of the AC75 is somewhat to windward of the centerline, owing to the position of the windward foil, but nothing like the relative position of the center of gravity of the Moth. The vertical force is generated to leeward of the rig. Since the cant angle of both the windward and leeward foils can be controlled by the crew, it's possible to have a range of heel angles for the hull and rig without any change to the cant of the foils relative to the water. If you take the heeling moment about the leeward foil, there may be a small reduction in the heeling moment from rotating the hull & rig to leeward. But there would also be a downward force that increases the drag. Heeling to windward would generate a upward force, but increase the heeling moment. Since these aspects have opposite effects on the boat's performance, it will require a VPP and experience on the water to see if there's a net benefit from heeling, and in which direction it should go.
     
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  6. Doug Halsey
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    Doug Halsey Senior Member

    I've been told by a DN iceboat sailor that the extreme mast bend commonly seen on those boats creates a downward force that helps the runners grip the ice. That sounds like a similar effect to leeward cant, but possibly varying more with the apparent windspeed. I would like to hear your thoughts about that.
     
  7. tspeer
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    tspeer Senior Member

    The DN does use extreme mast bend. (Those masts are straight when unloaded!)
    [​IMG]
    The lower part of the sail is canted to leeward and produces down force, as you suggest. However, I think the mast bend is as much about controlling twist as it is about canting the rig.

    Landyachts and iceboats sail close-hauled all the time, and there's not much movement of the boom as you trim the mainsheet. Instead, the boom moves more vertically, and mainsheet trim has the effect of controlling the leech twist. The apparent wind speeds upwind are roughly equal to the boat's speed downwind, say 40 - 80 kt, so the sail is effectively operating in a gale and the potential loads are very high. As the leech sags to leeward, it would take a lot of leech tension to keep from twisting off. The DN compensates for this by effectively keeping the leech in position and moving the luff to leeward to reduce the twist.
     
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  8. Doug Lord
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    Doug Lord Flight Ready

  9. OzFred
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    OzFred Senior Member

    Absolutely fine. My tipping point was 15kn of breeze. :)

    My issue with Doug is that he made insulting comments about JB Turner based on a misrepresentation of what he said. That should not go unchallenged.

    Turner's point was a hypothetical opinion should recreational sailors adopt AC75–like foiling boats. Doug has taken it as a general comment about recreational sailors in foilers and made disparaging remarks as a consequence.
     
    Last edited: Apr 18, 2019
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  10. OzFred
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    OzFred Senior Member

    That's sort of what I was trying to say, but not so eloquently of course. :)
     
  11. OzFred
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    OzFred Senior Member

    Also because the consequence is just a small amount of additional friction from the increased downforce on the leeward skid/wheel (given that they are virtually frictionless compared to a boat hull or hydrofoil).
     
  12. Doug Lord
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    Doug Lord Flight Ready

    =========================
    That is false-I did not misrepresent what he said-see post 691 and I don't consider my comments insulting but rather simply pointing out that JB's comments regarding recreational sailors were wrong which needed to be done.
    See post 682.
     
    Last edited: Apr 18, 2019
  13. Doug Lord
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    Doug Lord Flight Ready

    2019 RS windsurfers with windward rig heel:

    RS windsurfers 2019 windward rig heel.jpg
     
  14. OzFred
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    OzFred Senior Member


  15. CT 249
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    CT 249 Senior Member

    The main reason they are using windward rig heel is that without it, the sailor exerts no righting moment. Windsurfer racers normally try to keep windward rake to a practical minimum to power up, which is why many top racers hang on to the uphaul rope - it allows them to keep the rig upright when the sailor leans back for righting moment.

    [​IMG]

    Here's more information on why the rig should be upright rather than raked to windward, by a top Formula racer;

    Power to Weight: Your Stance vs Antoine’s - CarbonSugar.com https://carbonsugar.com/racing/power-to-weight-your-stance-vs-antoines/

    This is Antoine Albeau, the world's top high-speed racer, setting a new world record. Note how little windward rake he has;

    [​IMG]

    A significant reason for windward rake is probably really to depower (by reducing the apparent height of the rig) and to allow for the change in centre of effort and CLR in higher winds. The original Windsurfers had more windward rake (as shown below) because of high-drag rigs and the need to change the CLE to match the CLR - NOT because it's faster.

    [​IMG]
     
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