sail aerodynamics

Discussion in 'Hydrodynamics and Aerodynamics' started by Guest, Mar 21, 2002.

  1. Mikko Brummer
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    Mikko Brummer Senior Member

    Well, while the mainsail CL is about 0.8, the jib can be about 1.6.
     

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  2. daiquiri
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    daiquiri Engineering and Design

    It shows the proportion of lift coefficients between two elements, not the amount of lift carried by each one. ;)
     
  3. Mikko Brummer
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    Mikko Brummer Senior Member

    Touché, Slavi, but under the effect of these current rating rules jibs tend to be as large as mainsails. And I admit exaggerating a bit (for the sake of drama), it's more like 1.5/1.
     
  4. Petros
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    Petros Senior Member

    Nice graphic. I am just guessing based on my previous experiance in aerodynamics, but from that graphic I would think you could improve the main sail CL by flattening the last half TE of the jib, though that would reduce the jib Cl somewhat. That would likely improve the overall L/D, if that is an important objective on the sail (depending on other conditions) because it appears there is separation on the TE of the jib, fixing that should improve the flow conditions over the main sail.

    Of course, it is somewhat more difficult to get a better shape out of the jib and still have it easy to handle and stow quickly.

    Interesting to see these kinds of analysis on sail configurations, we have been doing this kind of thing on aircraft wings, with more primitive and way more costly tools, for about a half a century.
     
  5. PI Design
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    PI Design Senior Member

    This really shows the importance of good battens!
     
  6. brian eiland
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    brian eiland Senior Member

    Wild Oats XI.jpg

    Interesting deployment of multiple headsails, ..and their varying angles of incidence
     
  7. Mikko Brummer
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    Mikko Brummer Senior Member

    This makes no sence, the staysails all inside the code zero are useless. The multiple jibs should overlap each other so that the leech of the outermost jib is always farthest forward and so on.
     
  8. Mikko Brummer
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    Mikko Brummer Senior Member

    However, I tend to disagree a little with Mark Drelas post with staysail plot. Obviously, the staysail has no effect whatsoever in a 2D-plot, if it's shaped & positioned like a streamline in a plot without it. Like Mark mentions, the gain from a staysail comes from being able to sheet further in the mainsail without stalling it.

    The double head rig can be very effective on a reach, usually with a high-clew jibtop at the bow, overlapping slightly a deck sweeper staysail - the combination is more powerful than a single, larger reacher. I have a very concrete memory of this, once winning a Round Gotland race with a double head rig... This was in a 80 foot Grand Mistral, against similar one design boats - we had not measured in a large reacher, and the competition was gaining on us until we hoisted a staysail inside a small blast reacher (high clew jibtop). The speed jumped from 13,5 to 15 kn, against 14,5 kn for the opposition with a large reacher. Sorry for the poor quality of the pictures, from a VHS video of the race.
     

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  9. philSweet
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    philSweet Senior Member

    It may have as much to do with structures as aerodynamics. And it does look like they are on beam reach, hanging on to a light air sail, and dividing the load on the mast, letting the runners do their job. Also keeps the crew busy. Never underestimate the value of conspicuous busywork.
     
  10. markdrela
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    markdrela Senior Member

    The staysails will almost surely reduce mast drag compared to what the code zero alone would produce. But they will also add their own profile drag, which may or may not offset the lower mast drag.

    One thing for certain is that the staysails add complexity to the rig.
     
  11. philSweet
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    philSweet Senior Member

    If they are running a bit deep for the cut of the sail, perhaps the staysails can improve the performance around the edges of the design envelope?

    The staysails would also reduce the energy needed to constantly trim the code zero. Control speed might very well trump static efficiency.
     
  12. brian eiland
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    brian eiland Senior Member

    Multi-element Airfoils

    Wild Oats, headsails.jpg
    When I look at that deployment of sails on Wild Oats I am reminded of AMO Smith's multiple element diagram that I posted previously on another subject thread:
    Multi-Element foils.jpg
    When I look at Wild Oats I see a VERY BIG slot between the mast and the code zero sail,....so large that I suspect the code zero sail would not be generating as much forward driving force that it appears to be able to do in this photo. It actually needs at least one of those additional headsails, preferably the forward one?

    Or was this boat owner just over-sold a bill-of-goods by the sailmaker?


    PS: I suspect the smaller 'cutter type' headsail in that photo might be extraneous,.... as Avril Gentry has pointed out in his 'cutter discussions'
     
  13. brian eiland
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    brian eiland Senior Member

    Marchaj has passed away

    Don't know that I understand the late notice I received about this (only a few days ago), but it is yet another big lost to the sailing world.

    This is one of the primary gentleman I studied to learn more about the technical aspects of sailing aerodynamics.

    And it was only a few days ago that I pulled out my copy of "Aero-Hydrodynamics of Sailing" to review his explanations (wording and diagrams) of sailing aero verses some of the explanations by the airplane guys.

    For some reason I can understand his explanations better. I'm sure some of it is a result of slightly different definitions, interpretations, and visuals for the same terms such as lift, upwash, etc, etc.

    RIP, Mr Marchaj
     
  14. Doug Lord
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    Doug Lord Flight Ready

    CA Marchaj

    Thanks, Brian. What an inspiration he was to me!
     

  15. daiquiri
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    daiquiri Engineering and Design

    Sad news, thanks for reporting it. :(

    Marchaj has brought science into the world of sailing and yachting, which were then mostly guided by personal opinions and by rules of personal thumbs.
    He was a sort of icebreaker in this field, and he will be stay remembered for sure.
     
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