Pitchpoling - Designing it out

Discussion in 'Multihulls' started by Capn Mud, Apr 26, 2008.

  1. Capn Mud
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    Capn Mud Junior Member

    See the High Wind Video: http://www.norbanks.com/weta_video.htm

    And the capsize recovery one on this site: http://www.sailweta.com/videos.html

    Now the speed looks fun - but why the pitchpoling? That doesn't look so fun - especially in that cold NZ lake AND given how long it took to come back upright - wouldnt wannt be in a hurry (or a race!!!)

    Couldn't it have been designed out by:
    - Making the amas the same length as the main hull - or at least extend forward to in line with the bow; and/or
    - Giving the ama bow a long overhang or an upturned bow a bit like a Hobie? (Granted this would have a negative impact on its aesthetic appeal - but even so)...

    Or is there something I have not considered properly such as additional weight , strength of a longer ama or something?

    Any ideas from those more learned than me?
     
  2. waikikin
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    waikikin Senior Member

    Looks like a cool & fun boat, most times they poked it in it reversed out & kept sailing, maybe a higher volume & length ama might set up some keen one hull action but would probably require heaps stronger connective structure. All the best from Jeff.
     
  3. Doug Lord

    Doug Lord Guest

    Using "foil assist" as I've described in the other thread would allow the boat to convert that energy into forward motion and reduce the incidence of pitchpole dramatically. It would be the least expensive mod that could do that. That "high wind" video was shot in 30 knts and it is flat remarkable that their righting system works so well! Most sane people would not use so much sail area in those conditions but the Weta guys said they did it to test the boat. It's the behaviour of the boat in those conditions that leads me to believe that a "foil assist" mod could be offered for the boat -and even a bigger rig with those mods. I'm guessing but I think the thing is probably strong enough. If I were you I'd ask the Weta guys about it.
     
  4. idkfa
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    idkfa Senior Member

    30 Knots?

    Doug Lord how can you tell the wind speed? Was it stated? While being flat, I'd still expect to see white caps but don't at all, at very least during the gust. At best I would say 18-20Knts. sorry.
     
  5. Doug Lord

    Doug Lord Guest

    Wind

    ===============
    There was a thread about this on Sailing Anarchy and a representative of the company said the wind on that video was 30 knots.
     
  6. sharpii2
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    sharpii2 Senior Member

    Hi, Capn.

    1st) reduce the rig height or, in other words, reef.
    2nd) put a pronounced 'V' deck on the floats, so that when they go under, the don't act like dive planes, and
    3rd) possibly put planing surfaces on them so they don't get driven under in the first place.

    Other than that, all you'll end up doing is putting a bigger boat under the same sails.

    Bob
     
  7. CTMD
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    CTMD Naval Architect

    A note on that video..... (as explained at sailing anarchy a while back)

    The video was of a group of guys testing just how hard the boat could be pushed, basically trying to pitchpole. I doesn't represent the normal behaviour of the boat.
     
  8. grob
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    grob www.windknife.com

    The simplest system is probably to replace the normal rudders with T-foil rudders, this is beginning to be used on many beachcats.

    Gareth
     
  9. Capn Mud
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    Capn Mud Junior Member

    T-Foil rudders

    Hi All,

    Thanks for the helpful comments. I know they were pushing the boat awful hard - my point I think was that couldn't she have been relatively easily designed so that you had to push even harder to make her pitchpole. A qualified yes here from Chris Ostlind http://www.boatdesign.net/forums/showthread.php?p=198693#post198693 (Thanks Chris for explaining to this neophyte)

    Gareth, Now I assume you know what you are talking about here (and that I dont) but if T-foil rudders cause lift then dont they lift the sterns up relative to the bows and potentially cause earlier pitchpoling??? What did I miss here?

    Cheers,
    Andrew
     
  10. grob
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    grob www.windknife.com

    Andrew,

    No they work the other way around, when the boat is sailing normally, i.e. well trimmed the foil is parrallel to the direction of travel and parrallel to the hulls. So no lift is created in normal sailing.

    However if the boat starts to pitchpoll the foil nose points down (the same as the hull) this foil then pulls the stern down into the water preventing the pitchpolling.

    All the best

    Gareth
     
  11. Capn Mud
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    Capn Mud Junior Member

    Oh OK - thanks - makes sense now.
     
  12. oldsailor7
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    oldsailor7 Senior Member

    I would like to hear Richard Woods take, on this one.

    It's not as simple as it sounds. :(
     
  13. masalai
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    masalai masalai

    In my view (just a grumpy old ******* pontificating still) you cannot design out stupidity and still have reasonable sailing performance, but good luck in your attempts...
     
  14. TTS
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    TTS Senior Member

    http://groups.yahoo.com/group/LR2ACATS/
    This is a link to a yahoo group for the LR2 A-Cat. One of the issues that richard Roake looked hard at in this design was to limit its tendency to pitchpole. Evidently they have had a great deal of succes with the design. I think that they are making minor modifications as time goes on, but you can push this boat and is does not want to pitchpole.
     

  15. masalai
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    masalai masalai

    The DIFFERENCE is in reducing the tendency (wholeheartedly agree, as that is a realisable objective) as opposed to designing it OUT.... which is a folly...
     
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