Experimental Split Sail Design

Discussion in 'Hydrodynamics and Aerodynamics' started by Philip, Jul 7, 2020.

  1. messabout
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    messabout Senior Member

    Try to persuade yourself not to think in terms of "Unique". Sails have been steadily improved for hundreds of years. Any improvement is based on at least a rudimentary knowledge about what causes sails to move the boat. The drawing you have shown us ignores basic principles of sail design.

    You have a ten foot boat that can be driven, including to weather, by a simple unarig. Consider that there are countless boats that are very efficient with only a mainsail. The Optimist pram for example, works pretty well and it has about as simple a rig as you can imagine. Look at how well a Laser performs with a single sail, Look at the performance of the RS Aero, the Hobie 14, the Finn,... and on and on.

    If you want to go sailing then use a conventional sail and enjoy the fun. If, on the other hand, you are compelled to dream up odd ball stuff then do not expect to succeed with something that makes no aerodynamic sense. A shrewd old Guy named Phil Bolger has done a book that describes 100 different sail rigs. Get that book. It is easy to read and has valuable homespun information. After that, you might get Tom Whiddens more technical book titled ; The Art And Science Of Sails. Absorb the information from those books and you will have a starting place to begin the design of something that will actually work.

    I mean no discredit to you and I still urge you to keep thinking.
     
  2. Philip
    Joined: Jul 2020
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    Philip Junior Member

    Rumars: thanks, I guess those rigs are the practical application of what I had in mind. I was thinking to get everything to one side of the boom so that the sheet could be let out and the whole sail area depowered in a flash if needed. It looks like these designs keep the jib to about 20% of total sail area for this reason.

    Messabout: That's what I'll do. I'll look at the simple boats you mention and get a better sense of how their rigs function and are made.
     
  3. JRD
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    JRD Senior Member

    Philip, do you have some drawings or photos of your sailboat? There is probably a very practical solution available to get her pointing nicely.
     
  4. Rumars
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    Rumars Senior Member

    You seem to have enough leeboard area for your sail area, but what is this "knife edge at both sides" business. Is it eliptical in cross section?

    Please study the PD Racer class, it's a similar sized boat and they experiment with every rig in existence. Puddle Duck Racer - Easiest Sailboat to Build and Race http://www.pdracer.com
     
  5. Philip
    Joined: Jul 2020
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    Location: New Mexico

    Philip Junior Member

    Rumars, the leeboard cross section is not really elliptical... more uh, lenticular? The edges are at least butter-knife sharp. Maybe that's what elliptical means in this context. Anyway, I've solved my upwind problem. Yesterday I pulled the sail off and sewed it up into a much more aggressive airfoil shape. I didn't measure the belly (depth?) of the new shape, but I'd say it's about 8". My sail is a rectangle 6' wide and 8' tall, so the shape I put in it seemed almost cartoonish, but...

    Today I took the boat out to the lake and the difference was night and day. The wind ranged from dead calm to a reasonably brisk 15 knots (my guess) and performance was drastically improved under all circumstances except downwind, which was about the same. I was practicing close hauled and making decent speed (2 knots?) going quite directly into the wind-- my guess would be 35 degrees off from the wind. I have no way to really measure these things, but it was definitely closer than 45 degrees and at a moderate walking speed. I am surprised and elated by the new performance-- I can go anywhere I like now no matter where the wind is coming from! (up here in the high desert of New Mexico you're always surrounded by mountains and mesas, and the wind behaves something like water sloshing around in a bowl)

    So it looks like rather than sail configuration, I should be looking at sail shape. The shape I have now, which I'm sure is far from perfect, I arrived at from watching a very cursory youtube video. Do y'all know of any online resources for sail design information?
     
  6. Rumars
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    Rumars Senior Member

    I am glad you solved it. Enjoy.
     
  7. messabout
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    messabout Senior Member

    Phillip, take a look at: Sailcut.com. There is good stuff there. After that you can get the book; The Sailmakers Apprentice, it is a valuable reference for the person who chooses to make his own sails. It also has value in assessing the effectivness of whatever sail you might be using.

    Pleased to learn that you have addressed reality and fixed your sail so that it actually works. No need to try to improve the sail for direct downwind work. A rusty beer sign of the same size as your sail will work almost as well. Next thing you need to work on is how the downhaul tension, leech tension, outhaul tension and vang tension, or lack of it, affects the way the sail works..........or fails to work. A sail behaves not unlike a piano or Oboe. Tuning makes a lot of difference in the music that it can produce.

    If you are a serious student of the way sails work, you need go no farther than this very forum category. Take a look at the writings of Tom Speer or Mikko Brummer. They have some heady stuff to share with us. Their posts are pretty technical but reading them can introduce you to the more esoteric concepts of sail design and performance. Be assured that either of these contributors and a few others are exceptionally competent in their field of aerodynamics of sails.

    About your leebord. A knife edge on the front is not the best of design. Nor is a knife edge on the trailing edge. The leading edge should have a slightly rounded configuration ( parabolic actually but rounded will do).........maybe with a radius of five percent, plus or minus, of the thickness. The trailing edge needs not be knife edge sharp. By the time the waterflow reaches the trailing edge it has gone turbulent and no longer sticks to the surface of the board.
     
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  8. Philip
    Joined: Jul 2020
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    Location: New Mexico

    Philip Junior Member

    Thank you.
     
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