High Performance MPX Foil/Self-righting Trimaran-The Test Model

Discussion in 'Multihulls' started by Doug Lord, Dec 28, 2010.

  1. Doug Lord
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    Doug Lord Flight Ready

    MPX Test Model

    The hydrofoils control pitch and roll on this boat-the main foil uses a wand surface sensor to keep the boat at about 10-13 degrees angle of heel and the "trailing" rudder foil automatically controls pitch. If the angle of heel should greatly exceed 13 degrees the wind pressure on the curved pieces could tend to accelerate a capsize. However, the foil system is designed to prevent this automatically but because the skipper can bypass the wand system it is possible for the skipper to exceed a safe angle of heel, but not likely. But in "normal" sailing the vertical lift from the curved pieces is probably negligible.
     

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  2. boradicus
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    boradicus Senior Member

    Doug, thank you for the explanation. Do the rear hydrofoils elevate above the waterline inside of your 10 degree / 13 degree angle margin, or are they designed to stay sub-surface? I really don't know much about hydrofoils but it is very interesting to me!!! :D
     
  3. Doug Lord
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    Doug Lord Flight Ready

    MPX Test Model

    The foil system I have designed for this test boat is very unique so I can't show you any examples-yet except a concept model that you can find in these pages-the MPX 12. But, simplistically the main hull foils are like a Moth and the single ama foil is like the main foil on an AC 72. The system is designed to allow all the weight to eventually be supported by the single ama foil with the main foil unloaded except to control(with the rudder foil) pitch and heave(altitude-heeling angle).

    The picture on the left below shows a Moth with a wand surface sensor and mainfoil that takes about 80% of the load and a rudder foil that takes about 20% of the load. This is the same foil arrangement as on the main hull of my boat.
    The picture in the center shows my single ama foil that operates partially like an altitude controlled surface piercing foil-speed regulates altitude similarly to the single main foil on an AC 72. Next to it on the right is a recent picture of TNZ's retracted main foil. My foil has a lot in common with the TNZ foil except the the radius of the daggerboard is greater allowing a wide range of speed befre the foil would have to have a manual adjustment of the angle of incidence. It's more complex than that but that gives you an overview.
     

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  4. boradicus
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    boradicus Senior Member

    Doug, that is neat! I should read up on both the Moth and the TNZ. At the moment I am trying to comprehend basic boat design by reading Skene's Elements of Yacht Design, while I wait on another more recent book that incorporates more about multihull designing. I think hydrofoils are cool because of the greatly reduced wetted surface area, and because in some ways they are purportedly more stable systems, which I am assuming has to do with a reduction in wave turbulence and resistance.
     
  5. Doug Lord
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    Doug Lord Flight Ready

    Foils

    This is a good practical book on hydrofoils-a good place for anyone interested to start: "Hydrofoils Design Build Fly" by Ray Vellinga, Peacock Hill Publishing, Gig Harbor, Washington
    ISBN # 9780982236116
    contact: patvel@peacockhillpublishing.com
    May be available at Amazon.
    Written in a style suitable for most people.....
     
  6. boradicus
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    boradicus Senior Member

    Thanks! I'll look into it. :)
     
  7. Doug Lord
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    Doug Lord Flight Ready

    MPX Test Model

    I'm working on the foils:
    1) Daggerboard-to be built in matched halves of a styrofoam mold-glassed. The styro is carved to match the section and planform(20.5 X 3"). The mainfoil is 18" below the bottom of the boat. The lower portion of the board will incorporate solid carbon rods that will insert thru the main foil and add tremendous strength to the mainfoil/daggerboard joint. The board will also incorporate a hollow carbon tube for the carbon flap pushrod.
    --
    2) The rudder will be made of balsa and carbon, 20.5" X 3" above the waterline and 2.5" below the waterline. The rudder hydrofoil is 15.66" below the bottom(at the point the daggerboard exits the hull) and 17" below the waterline at static. The rudder will also incorporate solid carbon rods to reinforce the joint between it and the rudder hydrofoil.
    --
    3) The main foil and rudder foil will be made out of Dragon plate carbon sheets, and unicarbon hand shaped. Only the main foil will have a flap using .002" mylar ,with adhesive backing, for the flap hinge. The joint between the foils and the boards will form a sort of bulb to allow extreme reinforcing.
    --
    4) The ama foils are being made from matched halves of styro molds(glassed)
    and precut to shape by Sharon Dixon. The sections and planform will be hand shaped. They will be virtually solid carbon and have the heaviest loading of all the foils.
    --
    5) the mainfoil, with the flap at neutral, will be set(to start with) at +2.5 degrees, the rudder foil at 0 degrees and the ama foil at about 1.5 degrees-all referenced to the static waterline. The angle of incidence on all foils can be adjusted precisely on the beach. All will have a T/C ratio of 9%.
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    Pictures 2,3 & 6 are the ama foil layout done on the "mold", #4 shows the planform of the mainfoil and rudderfoil, #5 shows the asymmetrical ama section and the daggerboard, rudder, mainfoil and rudderfoil symmetrical section.

    click for better view:
     

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  8. Doug Lord
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    Doug Lord Flight Ready

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  9. boradicus
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    boradicus Senior Member

    Nice molds! :)
     
  10. Doug Lord
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    Doug Lord Flight Ready

    MPX / SRT Test Model

    ============
    Thanks. The styro molds are "quickie" molds suitable only for a single pull of one foil.
     
  11. daiquiri
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    daiquiri Engineering and Design

    Doug,
    How do you intend to carve the styro block to the exact shape of the airfoil sections?
     
  12. Doug Lord
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    Doug Lord Flight Ready

    MPX- Test Model

    -----------------
    I have a jig for the shape and will use 80 and 220 grit sandpaper. I've successfully shaped many foils this way in the past-good enough for one off.

    Foil section jigs: click
     

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  13. boradicus
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    boradicus Senior Member

    It would be cool to have a 3D printer. I think I saw some going for between 400-500 USD - the smaller kind that you build yourself in a kit - although I believe that there are some small pre-built models now for around the same. I have wondered how you would scale up using a printer, for anything larger than the smallest of projects. You could probably create a thin shell in segments that you could epoxy together and then displace into a box-framed plaster cast... Might involve some CAD, but it would be good for more than a one off...
     
  14. Doug Lord
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    Doug Lord Flight Ready

    MPX / SRT Test Model

    The system I'm using is tried, proven and inexpensive. There are always other ways to do things but this way suits this project perfectly.
     

  15. boradicus
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    boradicus Senior Member

    Molds

    It is probably loads cheaper and easier too ! Anyway, great work so far :)
     
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