Manually hydrofoil on monohull powerboat

Discussion in 'Hydrodynamics and Aerodynamics' started by Sassriverrat, Oct 4, 2017.

  1. Sassriverrat
    Joined: Sep 2017
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    Sassriverrat Junior Member

    Good Morning,

    Ive been look at the concept of developing a monohull with a pair of foils- both at zero or extremely minimal angle of incidence while the aft foil either was on a pivot so as to make the angle of attack adjustable or so just a trailing edge to be adjustable. The concept, similar to a 1930s J3 Piper Cub with adjustable elevator angle of attack via hand crank, would allow the user to use the crank in conjunction with the engine throttles to get the boat to fly before "tuning" the foil out so the boat would efficiently fly at cruising speed (say 45knots). Ideas?
     
  2. Mr Efficiency
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    Mr Efficiency Senior Member

    You have to realise a boat fully supported by foils, is inherently unstable, unless the lifting surfaces are wide apart, to provide a righting moment on heeling. The lift can't be concentrated at the centreline. Hydrofoil supported catamarans typically don't clear the water, and rely on the immersed portion of the hulls to help provide the lateral stability needed.
     
  3. Sassriverrat
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    Sassriverrat Junior Member

    Ah I should have clarified- after foil would be either two L foils similar to the AC boats or a full span (beam) foil that attached at the chines.
     
  4. Sassriverrat
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    Sassriverrat Junior Member

    The boat therefor sits on a Tri-pod
     
  5. PAR
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    PAR Yacht Designer/Builder

    This has been done previously, though typically the angle of incidence is higher on the forward foil than the aft, so the bow starts to lose lift, before the stern and she settles down. An adjustable foil will work, though hand adjustment wouldn't be practical, as you'd have so many adjustments to make underway with varying condisions and sea states that you'd hand would cramp up in a few minutes. The adjustment needs to be automatic, either mechanically or electronic, if you expect a smooth, fairly level ride, without continuous porposing as you play catch up with a hand crank.
     
  6. Sassriverrat
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    Sassriverrat Junior Member

    It won't fly as nicely as an airplane? When in a Cub, once at altitude, I can adjust the angle of incidence on the leading edge of the elevator and literally be capable of letting go of the stick and she'll fly level (minus occasional turbulence).
     
  7. PAR
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    PAR Yacht Designer/Builder

    You kidding right? Unlike flying, the water changes its condisions; wave heights, flow, currents, contrary winds, etc., continuously. Maintaining level flight on a boat is much more demanding. Maybe you need to watch a video of a boat that's up on foils to see how much trim input is used, just to keep it up.
     
  8. Sassriverrat
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    Sassriverrat Junior Member

    But in terms of waves you're flying below the major turbulence of them and the area of the foil coming through the wave/surface is providing additional lift on wave crests and loss of lift in the trough although I should think going through waves capable of changing that force so drastically might question the sea state conditions anyway. But by adding engines, we've now just removed the varying forces that a sailboat (say America's Cup boats) experiences and removed a variable.
     
  9. Mr Efficiency
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    Mr Efficiency Senior Member

    In the hydrofoils of old, the stability problem was addressed by either a "ladder" arrangement of horizontal foils either side of the boat, or in place of that, canted foils that always were only partially submerged. Further submergence, in both types, added lift, and gave a righting moment. I suppose single horizontal fully submerged foils, achieve the same with automated angle of incidence control, but that would involve a whole nuther level of complexity.
     
  10. Sassriverrat
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    Sassriverrat Junior Member

    I wonder then if the design of a very very shallow,mmmm, v foil that with a center horizontal foil in between the two diagonal foils.

    The concept being that the diagonals would be tapered down to the horizontal foil and as the boat ran faster and faster it would reduce draft until optimal speed is obtained (where the horizontal is designed). I'm sure that has likely been done and I haven't found it yet, but all the concept of staying under a monohull and not wider than the beam. Make sense?
     
  11. PAR
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    PAR Yacht Designer/Builder

    Again, look at some videos of boats on foils, things will become fairly obvious.
     
  12. Mr Efficiency
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    Mr Efficiency Senior Member

    Maintaining stability in both axes requires either increased lift with further immersion, or sophisticated control systems that are well beyond the scope of amateurs. And I can't see how SC propellers can be used to advantage. Your propellors need to be in the water.
     
  13. Sassriverrat
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    Sassriverrat Junior Member

    Look at the Russian foils- they don't use flight controls and fly all day without a problem. My thoughts are to make the foils no wider than the beam of the boat but to lower KG, just lower the flying height to maybe 18" above the water.

    Regarding the props- my fascination with them and this project involves the concept that the propeller will be cavitating while up in the air do to the small distance between the foil and bottom of the hull- and I want the foil being roughly at the same distance from the bottom as the hub of he prop. Make sense?
     
  14. Mr Efficiency
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    Mr Efficiency Senior Member

    The immersion of the foils will increase with added weight, your props will be fully immersed and the motors will be loaded up by the increase in blade area. I really can't see how you make it work, or even get it to lift on to the foils.
     

  15. Sassriverrat
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    Sassriverrat Junior Member

    That makes sense. So modified idea- 1. The two diagonal foils have ailerons on them- both of them in the "up" position like a v-tail airplane will help force the boat to fly- manual control of these flaps then can trim back out and further allow list control if there are ballast issues (people, fuel, water, etc) that aren't moving quickly.

    The wheels go between the foil and bottom of the hull in regards to placement (the wheel will actually be behind the foil). These wheels, combined with oversized engines, make the boat almost* over-wheeled except that once the boat takes off, it's going to be efficient. The flaps allow me to ford some extra lift at slower speeds until I fall off the foils in which, yes, she's overwheeled and I have to turn the props slower.
     
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