Multi edged sail

Discussion in 'Multihulls' started by Fanie, Jun 7, 2008.

  1. Fanie
    Joined: Oct 2007
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    Location: Colonial "Sick Africa"

    Fanie Fanie

    Hello,

    I was reading some stuff on sails and an idea came to mind. Since it is the shape of the sail that creates the lift (vacuum) that drags the vessel foreward, it seems the more edges within limits ? one have the more lift you can get ?

    I have experienced this sailing a small tri that we added a jib to. The jib made extra power, but the wind going off the jib adds speed to the wind passing behind the main sail, hence I suspect adds to the main sail becomming more effective with the faster windspeed passing behind it.

    Also, there are some wind veins shaped like this for wind power generators. They seem to have more rather than bigger veins. Granted, it is not the same thing, but all makes lift from the wind to create propulsion.

    I have made a drawing... I apologise if it is not representing the most efficient setup possible but serves merely to indicate what I have in mind. The drawing represents one sail with multiple slots in it, each area shaped as a sail. Wind would be from the left..

    If this idea could work, then the direction of the leading edges can be made in any direction. A jib has vertical lift (direction of force is ~ 90 deg to it's forestay), however if the slots as in my drawing is vertical, then the force would be foreward and not upward at some angle.

    If it would be possible to make this, would it work ?
     

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  2. rwatson
    Joined: Aug 2007
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    Location: Tasmania,Australia

    rwatson Senior Member

    The concept is aerodymamically practical, but may be hard to do with a fabric sail.

    The idea has been used on a rigid computer controlled rig that had these small wing sections - the whole thing looked like a big venetian blind, with the sections rotating on the vertical axis.

    All the sections were mounting inside a large square frame that could be rotated 360 degrees. The boat did a couple of Atlantic crossings, but I didnt ever see much after the initial publicity, and I havnt found anything on the web either.
     
  3. RHough
    Joined: Nov 2005
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    Location: BC Summers / Nayarit Winters

    RHough Retro Dude

    The problem is that for the angle of attack to be the same (so each blade operates at the same C/L) the trim angles have to change fore to aft (jibs sheet at greater angles off center than the main). If the aftmost element is trimmed so that it provides drive the forward element will have a trim angle 5-10 deg greater, each element forward will need the same trim angle change. This severely limits the boat's ability to sail close to the wind.

    The multi blade theory works in turbines because there is no first and last blade, it is a circle and every blade effects the blade behind. This allows all the blades to have the same trim angle. If you put big gaps between sets of 3-5 blades each set would be more like a multi-element sail plan.

    The turbine is more like a propeller than a sailplan or wing. The idea does not transfer well ...
     

  4. Fanie
    Joined: Oct 2007
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    Location: Colonial "Sick Africa"

    Fanie Fanie

    I would think with those clean leading edges one would rather gain to windward, but it would be difficult to make. Not without a computer simulated design that can shape each part of the sail in any case. Expensive to make too, lots of detail.

    He-he, it's going to look like the sail is shreaded quite a lot ;)
     
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