sail aerodynamics

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

  1. schakel
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    schakel environmental project Msc

    Outrigger

    If you use an outrigger for a stay running from the top of the mast to the boom at the side of the ship you have what you want because it will bent the mast windward and you make the upwash effect even worse because you bend it even more towards the sky and therefore create more downward momentum in the mast. On th other hand it is just a small part of the upwash since most wind leaves at the backend of the sail.

    I heard these outrigger boom were forbiden in open 60.
     

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  2. Paul Scott
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    Paul Scott Senior Member

    Schakel- I was trying to remember a piece by Bogotaj on sails where he points out that sweep and taper effect the amount of twist needed for a sail. Which seems to imply that more powered up twist (not luffing) equals more forward power, as the top of the sail is pointed more downwind than the bottom. Can you quantify how much power loss upwash causes?

    Yipster, FWIW, Stradivarious, the new AC Tri, cants it's mast all over the place. If you haven't seen it yet, get on Youtube and search BMW Oracle Castleswreath. My wife and I video'd this, and it seemed to me that in addition to using cant to steer, they seemed to be playing with flow direction.
    Some have speculated that mast rake is part of what makes windsurfers go so fast. A lot of classes allow a lot of rake- Contender comes to mind. I think I saw somewhere that the more rake made the boat faster.

    Anyway, rake plus taper seems to equal more twist. And according to Bogotaj, fractional rigs too.

    Paul

    EDIT- I found the Bogotaj piece- 'How do sails work?' article by Paul Bogotaj. My printout does not have the web address on it. I hope it can be found via Google.
     
  3. schakel
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    schakel environmental project Msc

    Quantification of loss

    Loss of the main sail when under heel, but this is just high school physics, is the loss of wind compared to what you have with no heel. So the loss = cos*(angle of heel). in percentages of forwarding power.

    Loss by the angle of twist is university physics and it takes me al night to figure that one out. If I do you be overwhelmed by the differential equations and Integrals and I do think you are waiting for that.

    Main effect is what aeronautical engineers call down-wash which means the mass of air that is displaced by which angle per second.

    Do you have Aero hydrodynamics of sailing, by C.A. Marchai in your library. I have so I know where to find it. (The academic answer)
    But I do not have it here. If you are really interested I'll give you his equations as well.
     
  4. Paul B

    Paul B Previous Member

    Bogotaj works for North Sails and his article is on their website:


    http://www.northsailsod.com/articles/article6-1.html
     
  5. schakel
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    schakel environmental project Msc

    Fractional rigs

    I never knew why fractional rigs were used on my boats (a schakel and a dragon) Neither why the three top races have fractional rigs. (VOR, AC and Vendee Globe) I found it in the article from Paul Bogotai.

    Thanks
     
    Last edited: Oct 21, 2008
  6. Paul Scott
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    Paul Scott Senior Member

    Also why my ULDB Cruising sled (designed 1998) has a 3/4 rig.

    I'm wondering how the Musto rig compares to an A Class(ish) rig, given the taper and rake of the Musto, vs much less taper and very little rake for the cat. IC typical sloop rig too.

    Paul
     
  7. schakel
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    schakel environmental project Msc

    Hoyt boom for genua

    I ask this before but nobody could answer.

    Since you know something about it: How come the Hoyt boom was never used on fractional rigs. And then I mean a genua that goes halfway the jib of the main.

    What is the big benefit. the torque of the genua is controlled in a way that easily follows or prepares the main for optimal half wind forwarding power.

    Here is an nice picture of what I had in mind. But with an genua instead and a Hoyt boom that you can apply on long half wind legs.

    The yard is K&M who are terrific. Designer is van der Stadt.
    but Hoeke (Pilgim Project by Wally)
    and Gerard Dijkstra (Maltese Falcon by Perinni Navi)

    are also house designer.

    http://www.kmy.nl/
     

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    Last edited: Oct 21, 2008
  8. schakel
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    schakel environmental project Msc

    I found it.

     

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  9. yipster
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    yipster designer

    "Loss of the main sail when under heel, but this is just high school physics, is the loss of wind compared to what you have with no heel. So the loss = cos*(angle of heel). in percentages of forwarding power."

    trying to get that in the calculator but playing with a degree arc i see 5% surface loss at 20 deg heel, 25% surface loss at 45deg heel and about 75% loss at 75 deg heel, is that basicly the same idea?

    i like to have some idea but these calcs must be rough figers as sailcup, 3d wash or a winglet play a role as well
     
    Last edited: Oct 24, 2008
  10. schakel
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    schakel environmental project Msc

    the cos function in your calculator

    The cos function in your calculator is perfectly right. What I always have on my mind is the graph.

    http://www.ies.co.jp/math/java/trig/graphCosX/graphCosX.html
     
  11. Mikko Brummer
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    Mikko Brummer Senior Member

    1 person likes this.
  12. tspeer
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    tspeer Senior Member

    Fantastic article, Mikko!

    I especially liked the jet that impacts the lee side of the spinnaker - I'd not expected that.
     
  13. yipster
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    yipster designer

    http://en.wikipedia.org/wiki/Crab_claw_sail
    re-reading Marchaj sail performance i'm impressed again with the crab claw
    properly set it easy outperformes a bermuda or whatever other rig for that matter
    the crab claw was only briefly discussed in this thread i see so i bring it up again
     

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    Last edited: Mar 3, 2009
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  14. Paul Scott
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    Paul Scott Senior Member

    And later, Marchaj displays the amazing superiority of a high AR Gunter, which has left me totally obsessed......

    Paul
     

  15. brian eiland
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    brian eiland Senior Member

    Last edited: Mar 1, 2009
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