Roll Control using foils

Discussion in 'Sailboats' started by Wingz, Oct 19, 2010.

  1. daiquiri
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    daiquiri Engineering and Design

    Who or what is holding the "line from the bow to the stern" in place? Is it somehow bolted or glued to the water? ;)

    You are considering only rotation, but the boat is free to move sideways as well. That's the point you are missing there.
     
  2. Wingz
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    Wingz Junior Member

    The mast of a sailboat is a lever, the force of the sail rotates that lever around a line form the bow to the stern of the boat at about the waterline (the centerline). These wings equally are levers, which rotate around that same line and are placed very close to the mast. These wings are designed to counter the heeling force of the sails. That is the point of them.
     
  3. CutOnce

    CutOnce Previous Member

    Thanks for straightening me out. Especially appreciate your friendly, personal and ad hominen approach. Certainly reinforces your expertise and appearance of objectivity. Also appreciate your award of negative reputation points - it enhances the appeal of the boatdesign.net site - so people know exactly who is running the asylum.

    --
    CutOnce
     
  4. mark775

    mark775 Guest

    "...fluid dynamics, may I suggest the MIT course on this." - a lecture, not an entire course. The most interesting part of the lecture is him holding the chalk at such an angle that he can allow it to chatter and dot a line. The posted version of this does not mention Bernoulli and only Archimedes.
     
  5. Wingz
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    Wingz Junior Member


    True. The design is for the wings to be as oversized as possible. By that I mean that I want as much righting force as I can get. This for two reasons. The first to to be able to handle more extreme conditions.

    The second is the sideslip problem. By having one wing extended to where it provides too much righting force, then the other wing can be partially extended. The partially extended wing cancels out part of the righting force of the more extended wing, to balance the boat. At the same time they act as two keels for directional stability, with the more extended wing also providing the righting force.

    The next step to this is to separate the wings to perhaps a 120 degree angle. In this form using both wings with one more extended than the other, the excess righting force could be used to lift the boat, and perhaps even fly it above the water. Perhaps you know of someone at Club Nautico Roma that may be interested in the idea.
     
  6. Cheesy
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    Cheesy Senior Member

    It won in not so convincing style against trailersailors.... there were no modern sport boats in the fleet
     
  7. Doug Lord
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    Doug Lord Flight Ready

    ============
    Oh? According to SA:

     
  8. Cheesy
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    Cheesy Senior Member

    Do you belive everything you read on there? I looked up the actual entries and results a while ago
     
  9. BATAAN
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    BATAAN Senior Member

    I'd like to point out that they only work when they are in moving water. Say you're trying to work to windward in fluky air... puff, lull, puff etc.
    Here comes a puff and you head up, then it dies and you coast to a stop. Then while your hull is stopped, the wind switches 90 degrees and hammers you on the beam with a hard gust. What the heck keeps you from falling over before you (in this ideal world) accelerate and get stability from these things? How do you tie up alongside another boat? They look great for catching unseen crab pot warps in the dark.
     
  10. Wingz
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    Wingz Junior Member

    The width of the boat provides the basic stability in stopped or light air conditions.

    The boat I am working on is a 5 meter skiff with a waterline beam of about 1.2 meters. The mast is 9 meters, and the sail is 7.5 meters tall and 2.5 meters on the boom in a wing shape. I built it this way - rather skinny and with way too much sail to test out this problem.

    On the first time in the water, I had a day just like you are talking about, puff, then nothing, then puff from another direction then nothing. What happened was that very quickly the boat turned down wind and came up to planing speed, then stopped, several times. Then with a better gust, the boat headed across the lake(small lake) on plane, leaving very little wake, until at the other side the rudder hit something and was pulled off its mountings, where I had to be rescued. The boat simply went downwind almost level. This has nothing to do with my sailing skills, as I didn't have time to mess with the wings and was completely at the mercy of what ever direction downwind was.

    I mentioned above somewhere that we did capsize tests and it took three times(we had to practice), jumping high on the mast to capsize the boat.

    However, this is only with a 5 meter skiff. I would think that a larger boat would be built with more conservative measurements, particularly a wider beam proportionately(more space aboard?). Since the idea of all this is to eliminate ballast, the boat would sit higher in the water. Making the bottom flatter provides a planing hull that should give any cat a run for the money.

    I like the idea about the crab pots. A hook on the end of the wings could better my diet tremendously.:p
     
  11. BATAAN
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    BATAAN Senior Member

    Sounds like great fun. Check back in when you have 100 hours under sail in all conditions from flat calm to near gale. Be safe and wear your PFD. I really want to see how this works out.
     
  12. Cheesy
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    Cheesy Senior Member

    Post some pictures, it may make it easier for some of us to understand what you are doing
     
  13. Wingz
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    Wingz Junior Member

    Sorry about that, I have been trying to but I can't get that button or the manage attachment buttons to work. I am a newbie. Best I can do here is direct you to my site at:

    http://tampicoventures.com/Boats/Using Water to Fly.html
    or a pdf file at:
    http://tampicoventures.com/Boats/Using_Water_to_Fly.pdf

    I'll work on posting some images to the gallery. Thanks for the heads up.
     
  14. Cheesy
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    Cheesy Senior Member

    Ok I see what you are trying to do however it looks like you have missed a vector in your analysis, in the picture below from your website there should also be a vector perpendicular to the keel pointing to the starboard side of the boat (for this particular picture), it is the resultant vector of this force and the sail force that makes the boat go forward. Your proposed design reverses the direction of this vector meaning that the resultant vector is pointing close to the wind direction, you will go sideways/backwards. (Note none of this has anything to do with the healing of the boat, well it does, the lift from the keel and the sail both try and tip the boat in a traditional design)


    [​IMG]
     

  15. Doug Lord
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    Doug Lord Flight Ready

    This is a fairly simple analysis that after reading quickly seems to convey the missing information from your analysis, Wingz. It was copied from this website: http://www.real-world-physics-problems.com/physics-of-sailing.html
    I'm sure there are better explanations available but this should help you for now. Thanks to Cheesy for the inspiration to try to find this in a hurry. I hope it helps, Wingz.....



    The Physics Of Sailing — Analysis Of Lift

    The figure on the left below(and far right) shows the general case where the wind Vw is blowing at an angle θ from the horizontal. This creates a resultant force on the sails, denoted by Fsails, which points in the direction shown.

    Note that Vw is the wind velocity relative to the boat. This is not to be confused with the wind velocity relative to the water. If the boat is moving, these velocities are not the same.




    The force Fsails is broken down into two components: lift (which acts perpendicular to the wind direction Vw) and drag (which acts parallel to the wind direction Vw). Lift and drag are defined as acting in these two directions; a convention commonly used in the literature with regards to air flow over a wing. As it turns out, air flow over a sail is very similar to air flow over a wing. The two sails (as shown) are oriented so as to optimize the air flow around and between the sails and generate as much "push" force as possible, to move the sailboat forward. The flexibility of the sails allows them to mimic the behaviour of a wing and be oriented in a variety of different positions to get the most "push", depending on which direction the wind is blowing.

    The velocity of the sailboat (relative to the water) is denoted by Vboat. This velocity is in a direction skewed slightly to the right of the center line of the boat, by an angle α. This means that the sailboat does not travel "head on" through the water. It is necessary that the sailboat travel slightly off center (with some sideways movement) because it enables the keel to generate the necessary counter-force to resist the sideways force exerted on the sails by the wind. Consequently, some sideways movement is inevitable, but the keel keeps it (and hence α) as small as possible.

    The figure on the center and right below illustrates how the keel works.



    The keel behaves like an underwater wing, and the same basic physics of sailing applies, as explained above for the sail. The force FK is the force exerted by the water on the keel and hull, due to the angle of attack α the keel makes with the water streamlines. Most of this force is (intentionally) due to the keel, which is large and made to resemble a wing to create as much counter-force as possible in order to minimize sideways movement of the boat. Using the same convention as before, FK is defined as perpendicular to the direction of flow of water Vwater.
    The force FD is the drag force exerted by the water on the keel and hull, due to the angle α the keel makes with the water streamlines. Using the same convention as before, FD is defined as parallel to the direction of flow of water Vwater.


    .


    click on image: the image on the far right is a combination of the first two....
     

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