best rudder foil section for a catamaran

Discussion in 'Multihulls' started by rapscallion, Apr 24, 2012.

  1. rapscallion
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    rapscallion Senior Member

    I was wondering if there was a general consensus for the foil section of choice on a catamaran. Is NACA0009 the best? What sections do the A cats use? What are the best shapes?
     
  2. redreuben
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    redreuben redreuben

    I am not an expert rapper but I do know that you will need to provide some more info like; What sort of Catamaran ? transom hung ? Spade ?
    The experts here are talented but not psychic !
     
  3. johneck
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    johneck Senior Member

    NACA 00XX foils are generally good symmetrical foils. The 09 refers to t/c ratio and should be set by the required thickness for your application. The max thickness point of the foil is at 30% of the chord, so the leading edge is fairly thick, giving reasonable performance against stalling or separation at the LE. The design TE thickness is 0, which is a problem, so you will either need to truncate the foil or add thickness to the TE.
    I suspect that the planform shape might have more effect on the overall performance than the foil section shape chosen.
     
  4. daiquiri
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    daiquiri Engineering and Design

    Generally correct, especially for low AR and transom-hung rudders.
    Redreuben is right, more info about the boat is necessary. A-cat is a very particular racing machine, what is good for her is not necessarily good for a cat intended for different use, like cruising.
     
  5. Steve Clark
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    Steve Clark Charged Particle

    The 63 series has been pretty much gold for a while. They seem to go in and out of the water without ventilating very well. Apparently fairly common for windsurfers as well. I have used the 000 series and can say that they are more prone to suck air than the 63 series.
    SHC
     
  6. Jcatmad
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    Jcatmad Junior Member

    C both expert and Psychic
     
  7. waynemarlow
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    waynemarlow Senior Member

  8. PAR
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    PAR Yacht Designer/Builder

    The use of sectional shapes depends of several factors and no single section is best. In most well engineered foils, you'll have a few different shapes employed. Typically, you'll have the top sections of a suitable surface piercing type, which transitions into the sections that offer the best lift/drag attributes, for the preformance envelop expected. Often at the tip, the mid length sections transition again, to one that can help control eddie making. Plan form also comes to play, particularly in regard to shaping difficulties and tip vortice generation.
     
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  9. Silver Raven
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    Silver Raven Senior Member

    Gooday 'PAR' - good-on-yea-mate - - first time I've seen anyone address the change of foil section - as being of any significance - as it gets deeper in the water. First time we got close to getting it right - we were able to reduce the area of both c/bs & rudders by over 50% & in the end got much better controll & at reduced friction. The result was a 'world class championship' which we thought was just fine - at that time. We took it a few steps farther by way of - leading edge - back @ the bottom by 11% - - the trailing edge forward by 17% & the bottom of the foil much thinner as a %'age with the max thickness @ 55% back from the leading edge. Sure did work for us & I've used the same principle several time since then & all to good ends. Ciao, james
     
  10. PAR
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    PAR Yacht Designer/Builder

    Seems we've had similar results with foil tinkering. I've not any world championships under my belt, but have seen successes and some quite big differences in side by side trials.
     
  11. rapscallion
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    rapscallion Senior Member

    could you expand on that a wee bit?
    The catamaran I have is a G32.
     
  12. redreuben
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    redreuben redreuben

    Yep me too, sorry Silver, clear as mud !
     
  13. Tim B
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    Tim B Senior Member

    As has been said time and time before. If you're not racing, it doesn't really matter, in comparison to getting the planform right. Rounded at the front, pointy at the back and thick enough not to bend will serve you fine.

    Tim B.
     
  14. rapscallion
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    rapscallion Senior Member

    I bought the boat to race it.
     

  15. Tim B
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    Tim B Senior Member

    My point was don't get too hung up on foil sections. Other parts of the design will have much more influence. Notably planform.

    There is lots of info on planform on the web.

    Cheers,

    Tim B.
     
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