GC 32 super cat

Discussion in 'Multihulls' started by Doug Lord, Oct 15, 2012.

  1. Gary Baigent
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    Gary Baigent Senior Member

    Like air foils for steering too?
    These are interesting times. With higher speeds these boats are going to evolve into near aircraft. And Vestas Sail Rocket is only the start?
     
  2. hump101
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    hump101 Senior Member

    Steering, yes, but avoiding steering is one of the benefits. However, the really interesting aspects are when you share the lift between a foil and a sail, because the sail force is very sensitive to leeway, so you can have leeway coupling using a foil/sail combo to control heave instead of having to have it built into the foil geometry which invariably creates a higher drag and/or less RM solution (e.g. uptip foils, wand flaps, etc.).

    Your new pivoting beam boat would be the perfect test bed for an inclined rig by sliding the mast base along the beam to incline the rig, and rotate the beam to provide steering/balance, would be very efficient, easy to control, and give a big increase in speed, if you can engineer it suitably.
     
  3. Doug Lord
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    Doug Lord Flight Ready

    Can't find what I'm looking for so far. But I'm finding interesting tidbits from from Paul Larsen:
    The lower foil runs at 30 degrees to the vertical i.e. parallel to the wing. The transition part of the foil curves through 90 degrees with a 25 cm radius. The high speed waterline is expected to be slightly above the transition radius. The ride height of the boat is determined by the transition radius as the foil works like most surface piercing foils. The lower foil is actually slightly over inclined past 30 degrees to allow for it achieving 30 degrees when flexing under full load. The foil is assymetric and the leeway angles are expected to be very small i.e. less than a degree... depending on level of ventilation. It has to travel within a narrow band of tolerbale angles to avoid cavitation.
     
  4. Gary Baigent
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    Gary Baigent Senior Member

    How about this pathetic earlier attempt with an inclining rig on Sid, Hump. Trouble is we got a heavy gale the next night and the wing snapped (while positioned level to avoid sailing at mooring) at the pivot point - so i never got to actually sail the beast. Decided after that failure (rig needed a brace across top of the central pivoting area) to return (perhaps sensibly) to conventional wing mast.
     

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  5. CT249
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    CT249 Senior Member

    Thank for the civil reply. In response;

    1- Foilers aren't taking over all of high-end racing; events like the Olympics, singlehanded RTW races, Volvo, and perhaps the windsurfing world cup, TP52s etc are "high end" racing, chock full of pros.

    2- I certainly do not miss the point that most developments come from working class/middle class sailors; I'm very, very familiar with such people in the form of Uffa Fox, Bruce Farr, Peter Mander, Jack Holt, Charlie Cunningham etc. We will have to disagree about whether the sailing community takes years to accept change; the history of craft as diverse as the Sharpie (in both original and Lightweight forms), Laser, Windsurfer, Mirror and many others proves that they will take up new ideas very quickly, as long as it suits them and they can afford it.

    3- I was thinking of Moth foils, since very sharp people like Phil S and AMAC say you can't build a competitive one at home. You make a good point, though, it could be different with other types of foils and I was wrong to miss that.

    4- However, as noted there is still the issue that huge numbers of people sail in confined waterways that don't suit foilers in many ways, and that if people from such areas are locked out of "the future of the sport" then the sport will suffer.

    So it would be nice if those promoting foilers would just allow for the fact that sailing is a multi-discipline sport, and that (just as in other sports like cycling, climbing, swimming, skiing or air racing) the fact that one discipline goes fastest or is newer or more extreme does not make it "the future" or the best discipline - just like windsurfing, for example, wasn't "the future" when it was the newest, fastest growing and fastest discipline.

    Anyway, enough of that from me for now.
     
  6. hump101
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    hump101 Senior Member

    Yes, shame you didn't pursue this further, but ideally you also need to rotate about a vertical axis as well to improve balance. Not much, though, for a fast vessel, as AWA doesn't change so much.
     
  7. Doug Lord
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    Doug Lord Flight Ready

    Illustration from Yachting World(Matthew Shehan). This illustration shows a net vertical lift from the foil when the boat is flying:
    click-
     

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  8. hump101
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    hump101 Senior Member

    That's obviously completely wrong, and disappointing from Yachting world. If that was the force distribution the boat would take off and lurch to leeward. Ridiculous to make such a basic error for a Smith vessel.

    Edit: Assuming the rest of the figure not shown does not give an alternative force component!!
     
  9. Doug Lord
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    Doug Lord Flight Ready

    There is a more complete version of that sketch around but so far I can't find it.
     
  10. Gary Baigent
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    Gary Baigent Senior Member

    If I remember correctly, they experimented with a few types of main DOWNFORCE foil designs - and then ended up reducing the areas of the finally accepted version by some considerable amount. Need to re-read the information again though.
    Yes, that is inexcusable by Yachting World.
     
  11. hump101
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    hump101 Senior Member

    My memory is that the foil they cut down to try and reduce drag was the first super-cavitating section version, but the foil used to set the record was a different one with trailing edge air entrainment. I don't think they've released much detail of the final design, and not sure if it was also trimmed for length at some point.
     
  12. Doug Lord
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    Doug Lord Flight Ready

    SailRocket-last

    After much looking I found a version of what I was looking for. Remember, I said that the portion of the foil above the transition curve is designed for vertical lift:
    from www.sailrocket.com/node/497 (comments-"reply armchair")

    Yes, the foil is blunt above the transition (radius). The foil above the radius is affected by both the leeway angles of the boat and the pitch settings of the foil. Seeing as the upper foil is at 30 degrees to the HORIZONTAL, the horizontal pitch settings affect this section of the foil more than the more vertical lower section. The upper section of the foil is more responsible for generating vertical lift. If it generates too much then the back of the boat rises until we reach the transition (radius) of the foil where the vertical component lessens. If we go too far then only the bottom section is left in and that is angled so it is pulling down more than the rig is lifting i.e. we will have net negative lift and be pulled back down to the transition. The boat should seek balance around this transition. If we are riding too low we can increase the pitch of the foil to generate more lift on the top section or decrease the whole inclination/roll of the foil. Getting the right settings is key to making the foil perform. We are still playing with it.
    Cheers, Paul.
     
  13. hump101
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    hump101 Senior Member

    As can be seen in the photo's in that article, and others, the horizontal portion of the foil is not in the water at speed, so is not generating any substantial lift in this condition. If it was, then it would be fighting the lower portion of the foil, and just making unnecessary drag. However, looking again at the record run (different foil), a small portion of the upper foil does look to be immersed for most of the run, so you may indeed be correct and they are using a small portion of the upper foil to ensure close control of the foil immersion. If so, very good spot Doug!

    This would suggest there is more performance available from SR2.
     
  14. Doug Lord
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    Doug Lord Flight Ready

    That last comment by Paul is not the only reference to using the upper portion of the foil for vertical lift and there are many references to the curved radius of the foil as the "transition radius"-which he explained above as the transition between vertical lift and downforce and is the main altitude control geometry of his foil concept.(and why he refers to the boat as a foiler)
    The comment by Paul that I read years ago and kept me searching the last few days where he specifically references the upper part of the foil being used for vertical lift up to around 25 knots-remains elusive but his comment in my last post is ,perhaps, better for a more complete understanding of altitude control on SailRocket-at least the role the foil plays.
     

  15. Gary Baigent
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    Gary Baigent Senior Member

    Okay, the upper section is lifting, however that is small potatoes to the lower section's hard negative lift (just look at that spray from the hole it digs).
     
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