Foils (Bruce?) Question

Discussion in 'Multihulls' started by BobBill, Feb 1, 2012.

  1. BobBill
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    BobBill Senior Member

    I am naive on lots of things, foils included. I understand the basic principles and so on, but I ran across something that got me wondering.

    The idea was that a cat or tacking proa was fitted with two foils and, depending on tack, one tack would lift the leeward hull and the opposite take would pull it down.

    I thought about this for a time and am now looking to fill in the gaps.

    Does this work without underway adjustments? It appears to be like a three point foiling rig, motor or sail, to me. Or, am I in Oz on this?

    I understand this is basic stuff, but basics first, and I have not a clue. Seems old idea now a hot topic?
     
  2. Doug Lord
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    Doug Lord Flight Ready

    If it is a tacking proa then I don't see the need for two foils: one T-foil with a wand altitude control system would automatically do exactly what you describe.....
    Thats how the mainfoils work from tack to tack on the Osprey ,Rave and Skat. A tacking proa ,using the foil for righting moment, could have one foil on the small hull which would lift up when the small hull was to leeward and pull down when the small hull was to windward.
     
  3. BobBill
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    BobBill Senior Member

    Foils

    Thanks Doug. I will have to locate that link.

    When I read it, the idea of one foil lifting and the other being opposite, seemed to make sense, until I wondered what would happen when boat did a 180, where hulls were reversed re weather.


    Maybe the material was for shunter, but I thought it was for tacker.

    I will put link up when I find it. Idea sounded great and was noted to be old stuff from 60s even...
     
  4. Doug Halsey
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    Doug Halsey Senior Member

    Raptor 16

    Originally Posted by Doug Lord :
    .
    Here's a good example, but the incidence of the foil has to be changed when you tack or jibe : http://www.artformfunction.com/hydrovisions/

    This is built just a few miles from my house. I'm thinking of driving over & checking it out.

    Doug Halsey
     
  5. BobBill
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    BobBill Senior Member

    That is what I thought, Doug H, have to move the foils to change water flow like a wing...

    Boy, would it be nice if it was automatic...I will find that darn link.
     
  6. upchurchmr
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    upchurchmr Senior Member

    BobBill,

    When the Bruce Foil was invented (Edmond Bruce writing in AYRS in the 60's) they proposed a tacking proa with a single foil in the ama. His initial boat was rather slow but had a triangular foil or board at 45 degrees to vertical. No adjustment, but it worked on either tack. One to hold up the ama and on the other to hold it down. A later development used a rectangular board which could pivot similar to a leeboard. He raked it forward when the foil was to leeward and raked aft when the foil was to weather to better match the line of effort of the sail.
    This specific concept is not often seen now days. This concept was to prevent heeling , not to raise the boat out of the water. However, Hydroptere (sp?) has a similar inclined foil but on both sides of the boat and it does fly. Very much a different concept but the idea of lift on one side and pull down on the other is used there, as I understand it.

    AYRS still publishes the book. "Design for Fast Sailing" search on AYRS and they have a publications page. The format of the book is not very professional, but some of the articles have a good basis.
     
  7. BobBill
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    BobBill Senior Member

    Foils

    Mr. Upchurch, thanks. Will be checking that reference out.

    Yes, L'hydroptere was the exact boat I had in mind initially, even if large and I think a sort of tri, but with a proa design, like a smaller Slingshot, perhaps.

    In meantime, I found that link..."self-tending" caught my attention...and the idea of having those things rising and pushing down and then doing a 180 confused me.

    http://www.aegeanmarine.com/Concept.htm
     
  8. Doug Lord
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    Doug Lord Flight Ready

    =========
    BB, the would foil+wand I described would be 100% automatic.....The wand is adjusted for the flight altitude you want-anywhere from a couple of inches to a couple of feet. The action of the wand then maintains that altitude automatically.
     
  9. BobBill
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    BobBill Senior Member

    Foils

    Doug, can you up a link so I can visualize? Would work on a cat or proa? I am so dense.
     
  10. Doug Lord
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    Doug Lord Flight Ready

    ===============
    Here is a short animation about how the system works. The point where the flap is ,essentially, "lined up" with the foil is the flight altitude. If something causes the hull being controlled to move up the wand causes the flap to move up thereby causing the foil to create a force pulling the hull down.
    If something causes the hull to want to move down the wand moves the flap down causing a lifting force to be applied to the hull. The flap+foil creates a very large force and the wand maintains altitude very precisely. On a tacking proa the t-foil/wand would be mounted on the smaller hull,I would think. It would provide all the RM necessary with no crew movement.
    ---

    http://www.youtube.com/watch?NR=1&feature=endscreen&v=yuFwDm8t3IM

    Ketermans description of a system like this where the lee foil lifts up and the windward foil pulls down-same basic system:

    HYDROFOIL SAILBOATS IN GENERAL
    "Hydrofoil boats can be categorized into two categories; 1) Incidence controlled hydrofoils* and 2) surface piercing hydrofoils. The difference lies in the way the boat maintains the proper altitude above the water surface. A surface piercing hydrofoil boat maintains proper height by varying the amount of foil submerged. The boat raises up as the speed increases and reduces the amount of foil submerged and therefore the lift. The boat finds equilibrium at the proper altitude. An incidence controlled hydrofoil sailboat has a mechanism that controls the angle of attack of the foil to maintain the proper altitude. It is generally believed that surface piercing is simpler, but incidence control is more efficient. In reality, it is the method that works with fewer problems that is simpler.
    From the beginning it was felt that incidence control was better suited for a sailboat even though most of the existing hydrofoil sailboats were of the surface piercing type. There are many advantages of the incidence controlled foils; however, the most important is what I call the DLA (dynamic leveling affect). This is the increase in righting moment or stability due to the ability of the windward foil to pull down. The DLA has little affect on the low wind performance, but it essentially makes the top speed of the boat limited to the strength of the boat. Conventional boats with a finite amount of righting moment can only extract so much power from the wind, but with the DLA, the righting moment is virtually unlimited.Intuitively many people think that the added drag of the windward foil plus the increased induced drag of the leeward foil would offset the gain in righting moment, but calculations show and practice proves otherwise. The dynamic leveling affect not only produces a dramatic increase in top speed, but is also responsible for all the other key features that this stability provides.
    The other major advantage of the incidence controlled foils is they are less affected by the waves and other surface affects. Drag and losses associated with the surface are the major reason incidence controlled foils are more efficient.
    All hydrofoil sailboats have problems with ventilation; however, surface piercing foils have larger problems, because the foils are piercing the surface at a smaller dihedral angle which makes it easier to ventilate."

    ------
    * On the Trifoiler the entire foil was moved to control RM, lift and negative lift hence the term "incidence controlled foils". On the Rave the incidence was generally fixed at +2.5 degrees for the main foils though some owners found a way to decrease the incidence on the windward foil. Lift and negative lift on a Rave foiler is generated by the wand (designed by Dr. Sam Bradfield), a surface sensor(dragging in the water) and attached directly via linkage to a flap on each main foil. The wands are independent just like the trifoiler "incidence controlled" foil sensors.

    http://www.hobiecat.com/sailing/TriFoiler History Original/Magazine Articles/Multihulls 1990.htm
    ============
    Did this help, BobBill?
     
  11. Gary Baigent
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    Gary Baigent Senior Member

    Er, Hydroptere, to my knowledge, does not have negative (pull down) on its windward foil; they have water ballast for trim fore and aft and athwart-ships but the foil, although it can be lifted, doesn't have angle of attack changeability; it is fixed at 3-4 degrees (that's a guess) but my point is the float foils are not changed while sailing.
    This was different on the original Paul Ricard (fore runner of Hydroptere) which could cant its main beam fore and aft and also its dihedral ... and that could change the foil angles (also the T rudder had hydraulics to angle the blade) ... but Tabarly found that it was better to fix the foils at the required angle - and then he could dump all the heavy mechanisms and make a lighter, less complicated boat, which he did and then set a new Atlantic crossing record.
     
  12. Doug Lord
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    Doug Lord Flight Ready

    =======================
    You're 100% right on Hydroptere, Gary. Thanks for the info on the Paul Ricard.
     
  13. BobBill
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    BobBill Senior Member

    Foils

    Aye. H simply gains altitude...and it does it so well.


    Am still trying to digest the up/down system noted by Doug L. Fogged brain on this attribute needs clearing. If it works, it is nifty indeed.
     
  14. Doug Lord
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    Doug Lord Flight Ready

    ------------------
    BB, its the same basic system used on the Rave, Osprey, Skat ! When you look at the video it can be confusing because after takeoff and when the boat reaches flight height(when the flap and foil are inline) the hull keeps going up and the flap goes up illustrating that the flap is acting to stop the upward progress. There should have been a hesitation in that animation to make the flight altitude point more clear. In real life the hull rises to flight altitude and stays there-the wand on all the above boats holds it at the right height with the foil lifting UP or pulling Down as commanded by the wand to maintain the set flight altitude. The flight altitude can range from inches to feet and is fully adjustable.
    Don't hesitate to ask any questions that could clarify some points for you.
     

  15. cavalier mk2
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    cavalier mk2 Senior Member

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