Roll Control using foils

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

  1. apex1

    apex1 Guest

    Ahh, there we are, sponsors and investors.................:idea:
     
  2. Doug Lord
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    Doug Lord Flight Ready

    Wingz, Richard is right!

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    Until you understand this basic tenet of the physics of sailing your project is doomed:

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    This is 100% false because you misunderstand the meaning of "OPPOSE" in the context of sailboat design.
    You cannot OPPOSE a heeling force with a force acting in the same direction and parallel to the heeling force!! It is a physical impossibility.

    A heeling MOMENT is created by the force of the wind acting X distance from the center of lateral pressure.
    a righting MOMENT is created by a force acting X distance from the center of buoyancy.
    These forces oppose each other but act at approx. 90 degrees to each other as stated above. This is PHYSICS not someone trying to be mean, or a politician or anything but trying to help you understand a BASIC part of sailboat design.

    Again, the righting force MUST act 90 degrees to the heeling force. The righting force can be created by a foil whose lift vector is mostly vertically up or mostly vertically down, or by guys on a trapeze or in any number of ways as long as the force is acting 90 degrees to the waters surface which IS 90 degrees to the heeling force-NOT PARALLEL TO IT!!!!
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    Your mistake is to think you can create a righting force that acts parallel to the heeling force: CAN'T BE DONE-PHYSICAL IMPOSSIBILITY! You know, I've worked with foils for years-I believe that their proper application to monohull or multihull boats can improve speed and seaworthiness(in some cases) it can certainly improve speed. But you stand ZERO CHANCE of being part of the foiler revolution if you fail to understand the basics of sailboat design. Please give yourself a chance and try to understand this stuff!
    Below are pictures of three boats(I designed the models) that use foils to create righting moment.
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    Heeling Force-in sailboat design usually expressed as resulting from Heeling Moment. Heeling Moment is created by wind presure in ,say, pounds per sq.ft. applied to the sail(s) at the Center of Effort of the sails. So for a 200sq.ft sail with a CE at 11'(vertically above the Center of Lateral Pressure) and 1lb. per sq.ft of wind pressure the Heeling Moment is 2200ft.lb.. Heeling force acts parallel to the waters surface.
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    Righting Force-usually expressed as resulting from Righting Moment. Righting moment(for a monohull that is floating) is created by an amount of weight or lift(either up or down) at a certain horizontal distance from the center of buoyancy. So if this boat was level it would require 220lbs of weight (or lift) in any combination placed 10' from the center of buoyancy and resulting in a Righting Moment of 2200ft.lb.
    Righting force acts 90 degrees to the waters surface.
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    Side Force-in sailboat design side force does not result from a MOMENT-it is merely the lb/per sq.ft of wind pressure acting at the CE of the rig. This force must be "opposed" by an equal an opposite force generated by a foil that ,ideally(but not in every case), is placed 90 degrees to the waters surface. This foil needs to have an area based on the projected speed of the boat etc. There are rules of thumb that say-depending on speed, that the foil are should be between 1% and 2% of sail area. But there are exceptions,again based on speed: a Moths upwind daggerboard area is .8 of 1 percent of sail area-and thats because the horizontal foil is tilted to help produce the required force opposing side force of the sail. Side force acts parallel to the waters surface and is NOT the result of a moment.
     

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  3. Wingz
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    Wingz Junior Member

    So, If I put a foil horizontal, it will work, but if I put it vertical it will not. Correct?
     
  4. apex1

    apex1 Guest

    Senseless Peers, I said that already.............
     
  5. Doug Lord
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    Doug Lord Flight Ready

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    As long as the force from the foil is acting at 90 degrees to the heeling force and is separated by the proper distance from the CB(or CG for a full flying foiler)
    it will generate righting moment. But that is a long way from saying it will work! Other considerations come into play if you want to determine if the foil is better than ballast-like wetted surface, induced drag etc. A lot of the best designers in the world for high speed sailboats believe ballast is a good answer. Did you know that the fastest sailboat in the world-Hydroptere- uses movable water ballast? It does not use its foils to create RM!
    The guy who invented DSS-Hugh Welborne- uses a foil that extends from the lee side of a boat and generates vertical lift. The righting moment from that foil is a function of the distance of the center of lift from the center of buoyancy of the boat.
    Whether it works or not depends on whether the lift it creates along with the righting moment it generates results in a net increase or decrease of drag.
    DSS is the closest thing to your idea-at least the part of your idea that is closest to reality-the illustration with wings out at an angle from the hull. Remember that the lift from the foil MUST act at 90 degrees to the heeling force. And even with DSS the verdict is still out though Mr. Welbounes DSS25 recently won its first race. The DSS foil operates fairly close to the surface and to remain effective it must be at least 2.5 chords below the surface. If it broaches the surface or operates too close to the surface it will have too much drag.
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    Wingz, there really is a foiler revolution and thats why I'm so interested in the application of foils to sailboats. You could potentially play a part in this exciting development but you have to understand the basics first-otherwise you don't have a chance and will subject yourself to needless ridicule which some may try to use to damage the whole idea of foils making a difference. I'm pleading with you to try to understand these basic concepts so that you'll be freed up from your misconceptions and be able to make a real difference!
     
  6. Wingz
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    Wingz Junior Member

    Ok then, one more time. If I put a foil in the horizontal position, it will work. However if I put it vertical, it will not. Is that correct?


    There certainly is a foiler revolution going on, and the sooner we get rid of ballast and gravity based systems to keep us upright, and move on to where we use fluid dynamic forces both above and below the water, the better off we will be.
     
    Last edited: Oct 24, 2010
  7. BATAAN
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    BATAAN Senior Member

    Okay then, one more time. A foil must be moving to function. Many many times in sailing and maneuvering, the boat becomes so slow that a foil will not work. Ballast and gravity have the advantage that they are always functioning. Watercraft are highly complex dynamic systems and building up one narrow performance range can negatively impact others. I've mentioned this before but it just gets shrugged off with something about the hull is wide enough to stand up when still. Boats are not new, foils are not new, the entire environment is chaotic, unpredictable and often dangerous and one simple idea is not going to change physics. This may work under a narrow range of conditions in smooth water on an otherwise-useless daysailer when all angles, weights and forces are correct. If you go out on the "big water" you better have a craft that uses basic physics for stability at all times, without human control. In other words, you need a real boat that you can lie down in exhausted, cold and seasick and she'll take care of you when the feces hits the fan, it's dark, far far too windy, breaking seas from all directions test your stability etc etc etc. Sorry, I picked up too many dead people in my CG days.
     
  8. CutOnce

    CutOnce Previous Member

    It is however entertaining and it has kept the local frother in a bother.

    You have to give Wingz serious credit - he at least has built a full sized boat that allows testing and demonstration of his ideas. No little red models in Tampico.

    I wish I had thought of this concept a long time ago - invent a new character each month that tries to join/exploit the foiling revolution. Slap together a few pages on the weeb, add "Patent Pending" for instant credibility. Then have the new character steer the revolution into bad science shoal water. Hilarity ensues as our hero mounts his trusty steed and charges this month's windmill. Cut to commercial for West System Epoxy.

    Hallowe'en approacheth.

    --
    CutOnce
     
  9. Wingz
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    Wingz Junior Member


    I hear you. This boat was build only to test out or challenge several long held concepts of sailing in an effort to move us forward. As you say " It may work...." As far as the 'big water' goes, at 5 meters length, 1.2 meters waterline beam, and only a half meter in height, for now I'll stick with the lakes and rivers. When I get tired, I'll pull it out and go home to sleep in a bed. For the big waters, another boat, another time.
     
  10. BATAAN
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    BATAAN Senior Member

    I really admire your actually building and testing your idea. More of us should do so.
     
  11. Wingz
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    Wingz Junior Member


    Don't let me stop you.:)
     
  12. Wingz
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    Wingz Junior Member

    Thank you! Sincerely.
     
  13. Munter
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    Munter Amateur

    While I don't think the configuration proposed by the original poster works, I can think of a modification that could be made that might work and explores the area a little.

    During all the wing talk that has been floating around since the last AC there were comments made about using the top of a wing sail to pull to weather by sheeting it out to the point where it is sailing on the other tack. A similar approach could be tried with the underwater foils whereby the very tip of the board is rotated with the leading edge to leeward so that the tip of the board is effectively pulling to leeward. Of course, the whole board can't be used like this because of the easily identified leeway problem but if just the outermost 15-20% was angled while the upper sections of the board still performed as per normal resisting leeway the board might be able to produce a reasonably rotation moment that would improve the sail carrying power of a dinghy. Effectively the board would be trying to roll the hull to windward. Perhaps you would even use a longer board than normal to give the tip a greater lever arm to work off?

    Yes it would add to the drag and yes, there would be an inefficient discontinuity in the pressures around the foil but unlike in the aero case, the difference in angles of attack would only be a few degrees so I would have some hope that the extra drag would be more than compensated for by the increase sail carrying capacity

    In the spirit of the local frother I name this technology "Power Tip Technology" (TM pending). I am taking applications to licence the technology but I assign Wingz 1 free licence to explore this unique idea on his unique vessel. lol.
     
  14. BATAAN
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    BATAAN Senior Member

    A flexible, twisting board? With some sort of simple mechanical feedback loop that keeps it in a proper attitude?
     

  15. BATAAN
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    BATAAN Senior Member

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