best cross section for fixed masts on a proa schooner

Discussion in 'Hydrodynamics and Aerodynamics' started by lucdekeyser, Aug 8, 2017.

  1. lucdekeyser
    Joined: Aug 2004
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    lucdekeyser Senior Member

    I was wondering what the aerodynamic price is to pay to forego rotating masts or sails on a proa schooner and settle for fixed masts with a sail track in the middle of the lee side.
    I imagine three possible sections: 1/ circle 2/ elliptical lengthwise (flattened circle) 3/ a fat version of a Speer P30212 like foil
    I do not sure how relevant this article is "Flight in slow motion: aerodynamics of the pterosaur wing" but I get the impression that the aerodynamic performance advantage of the non-circular sections is not worth the potential trouble of lift from the bare poles when moored in very windy conditions.
    What is the sense of proportions weighing in the advantages over the risks?
     
  2. johnhazel
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    johnhazel Senior Member

    What about a rounded triangle to give you a drooped leading edge. The track would be on one of the rounded corners. That corner would point leeward at 90 degrees to the hull. The unused drooped leading edge would be in a relatively harmless area of flow.
     
  3. lucdekeyser
    Joined: Aug 2004
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    lucdekeyser Senior Member

    Yes, that is very clever. I suppose that as a bare pole this section would generate lift but intuitively less than the non circular sections mentioned in the opening message.
     
  4. rob denney
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    rob denney Senior Member

    We designed such a section using the Tom Speer method of wing mast designs where you take the leading edge of the full size foil, truncate it and mirror it. This gave us the leading edge which we then angled at 30 degrees to windward and mirrored it for the trailing edge. Looks pretty good, but the mast still needs to rotate in case you are caught aback (otherwise the battens break or the track is ripped off) and for when the breeze is not at 30 degrees to the boat.
     

  5. lucdekeyser
    Joined: Aug 2004
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    lucdekeyser Senior Member

    I understand that an isosceles angled at a base of 30° and rounded according to a Speer mast wing foil leading edge is a more sophisticated version of the John's rounded equilateral triangle.
    I am surprised that when caught aback the track may be ripped off - it is still somewhat better than the fate with a stayed mast but still - Wouldn't that also happen then with a fixed round mast with track to lee? Is that one of the reasons to argue for lacing the sail to the mast?
     
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