Calculate Sail Power with high Rouch ???

Discussion in 'Sailboats' started by Yacht Skipper, May 21, 2009.

  1. Yacht Skipper
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    Yacht Skipper Junior Member

    Hello,

    Does anyone know a sail power calculator that consider High roach.
    When I use the calculator on WB-sails, when I enter P, I etc...the resulted area is much inferior than my sail area.

    Can I just extrapolate the input until the sail area is matched ?

    Any help welcome.

    Kindest Regards

    Mat
     
    Last edited: May 22, 2009
  2. Omeron
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    Omeron Senior Member

    You mean Roach?
     
  3. Yacht Skipper
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    Yacht Skipper Junior Member

    Yep,

    Sorry my English is not that good
     
  4. Yacht Skipper
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    Yacht Skipper Junior Member

    Any help ?
     
  5. PAR
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    PAR Yacht Designer/Builder

    Typically you don't count the roach, nor luff or foot round, but with modern fat tops, it's lose in calculations can be substantial. Consider your calculations as if it was a quadrilateral sail.
     
  6. gonzo
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    gonzo Senior Member

    In a traditional Marconi sail, the top is basically worthless. It produces more drag than anything. As Par says a quadrilateral sail shape will approximate the performance. Full batten sails, with very stable sail cloth, are in some ways easier to calculate
     
  7. C 249
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    C 249 Junior Member

    Doesn't that depend on the mast and other factors? Lots of fast boats carry very small diameter topmasts, and practical experience shows that if anything goes wrong high up, you really feel the effects in loss of performance. And just adding roach to make a fathead sail certainly doesn't always add much to performance, as many practical examples have shown.

    And don't you find that WB Sails, Tom Speer etc show that many of the old claims that masts interfere heavily with flow over the main are incorrect?

    Certainly, practical experience shows very strongly that in the typical boat, a wingmast makes little difference in performance when compared to a good conventional mast. The predictions that many make would indicate that a wingmast would make a huge difference, but this does not occur in real life - ergo the predictions are wrong.
     
  8. Yacht Skipper
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    Yacht Skipper Junior Member

    Thanks guys,

    Then in order to get my sale power can I use those value to be close to reality:

    See pic.
    Black sail is the sail the way it is.
    Pink dashed line is the virtual sail used to get E and P inputs

    Thanks in advance
     

    Attached Files:

  9. gonzo
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    gonzo Senior Member

    C 249:
    A wing mast is a foil that produces lift. To the extreme, it it the sail itself. It produces a huge performance increase compared to a mast that is only a beam with drag. Bendy masts, when set wrong, affect performance. That is because if the top of the mast is not controlled properly, the set of the sail will be wrong. My practical experience shows very strongly different behaviour.
     
  10. Omeron
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    Omeron Senior Member

    You can try using a sail area calculator. There are i am sure several ones on the web. But the one i remember using some time ago was something like clara.net you will find if you google it. Although it doesnt give you the raoch area, you can play around with the coordinates, so that the leech line cuts the roach area in such a way to approximate. This calculator also allows you to introduce gaff length to play around with square tops.
     

  11. C 249
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    C 249 Junior Member

    You may be getting different practical experiences. I would be interested in hearing of proper trials against top class competitors on similar craft.

    My experience includes wing masts from about 3.5" span (the Bethwaite Tasar section) to about about 8" span (Formula 16 cat "superwing" section).

    The Tasar mast doesn't produce, in reality, the performance difference that is claimed (although it's probably faster than a normal stick). Frank BEthwaite proposed updating the rig and DROPPING the wing in favour of a "pole" mast.

    On the F16 it's harder to measure because there are no small-wing or pole-mast F16s 'round here. The first big-wing F18 was only very marginally faster than teardrop-shape masts, I believe, and was normally beaten by boats with teardrop masts.

    There have been wing masts in restricted classes since at least the 1930s. They have been tried in R Class/12 Foot Skiffs, Int Canoes, 18 Foot Skiffs, Gwen 12s, Merlin Rockets, NS14s, Moths, Cherubs, Flying Ants, Renjollen (I think) various yacht classes, etc.

    In other words, most of the world's top development classes have tried wing masts and then discarded them. That seems to be an excellent real-world test ground.

    The practical experience shown in those classes is that the wing mast doesn't produce enough extra performance to be worthwhile, with the exception of the NS14 and the Tasar (a "frozen" NS14) and perhaps the Finn, which have particular characteristics well suited to wings - for example in the NS14 the wing mast gives unmeasured area.
     
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