Manually hydrofoil on monohull powerboat

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

  1. Mr Efficiency
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    Mr Efficiency Senior Member

    You are making things very difficult by insisting on SC props. They really need a boat hull in front of them.
     
  2. Sassriverrat
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    Sassriverrat Junior Member

    Because the boat provides a flattened, consistent stream for them?
     
  3. Sassriverrat
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    Sassriverrat Junior Member

    I think one of my bigger fears is having a propeller below anything else on the hull?
     
  4. Mr Efficiency
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    Mr Efficiency Senior Member

    It provides a degree of shielding to regulate the running depth of the props.
     
  5. Mr Efficiency
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    Mr Efficiency Senior Member

    The props don't need to be below all your foil structure, just comfortably below the surface of the water. You could have the bottom of the props just high enough not to ground first, But there is another problem, you don't want anything dramatic happening when you ground.
     
  6. Sassriverrat
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    Sassriverrat Junior Member

    Certainly understand. Not so much worried about grounding so much as, in a purely slow displacement mode, pushing through mud and props rubbing, say, a log. Further, if the total distance from foil to bottom of the hull is only 36" or less, that's not leaving a lot of room on a 65x10.5' boat with 900hp between two engines (Detroit 671s)
     
  7. Mr Efficiency
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    Mr Efficiency Senior Member

    Naturally your slow mode draft has increased substantially. The whole idea is a highly technical exercise, there is far more chance of getting a "lemon" than tinkering around with boats that don't rely on getting wholly supported by foils. The calculations have to hit the mark.
     
  8. gonzo
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    gonzo Senior Member

    Planes operate in a single fluid: air. Boat operate at the interface of two fluids with a differenc in density of about 1:800. Also, the interface is not a plane but changes continuously and unpredictably (waves). Airplane type controls won't work.
     
  9. Sassriverrat
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    Sassriverrat Junior Member

    Well we know that airplane controls do work on a small scale- there's a few YouTube videos of guys running boats using a center stick to steer, lean, etc. but I understand what you're saying for a larger scale.

    So we are back to- if a surface piercing foil is to be developed to fly the majority of weight of the hull, can it be done in a stable manner AND not exceed the beam of the hull?
     
  10. gonzo
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    gonzo Senior Member

    No they don't work regardless of scale. You are referring to servos, which is very different. The controls are rudders, ailerons, elevators, etc. If fully submerged, like a keel, there are similarities. However, foils are not fully submerged but operate at the interface.
     
  11. Sassriverrat
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    Sassriverrat Junior Member

    servos are the name for elevator, aileron, etc control in the water? Because I've personally seen boats with a cable-attached stick to control pitch, roll, etc with a 6hp outboard behind the driver. And there are YouTube videos with similar boats and controls.

    But my question remains- for stability purposes, is it possible for a monohull to fly at low altitude above the water with foils not exceeding the beam of the vessel?
     
  12. Mr Efficiency
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    Mr Efficiency Senior Member

    I saw an electric powered hydrofoil surfboard story on TV the other day. The board was elevated well above the water, and all that was visible below was a central strut, I have no idea how the height is controlled.
     
  13. Sassriverrat
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    Sassriverrat Junior Member

    They've done a fairly incredible job with these- but to answer your flight question- simple- while the foil is lifting, the person simply leans forward slightly to cause the foil to dive to counter the lift. As someone that flies airplanes, I really don't seem that much of a difference between the hydrofoils and wings- yet some people are determined to declare them polar opposites. Hydro just operates in a incredibly higher density resulting in drastically bigger changes to equivalent adjustments.
     
  14. gonzo
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    gonzo Senior Member

    There are two dramatic differences. First, as stated previously, the foils operate in the interface between two fluids of different characteristics. Secondly, water is a non-compressible fluid. If you can't understand the difference of how a foil operates in a compressible and a non-compressible fluid, you need to start at the basic level of physics. People are not determined to declare anything. That is how the laws of physics work.
     

  15. Sassriverrat
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    Sassriverrat Junior Member

    Gonzo- I'm not saying that you are wrong by any means, but I think the technicalities are played too literally. The basic principles are the same and on the surface, they appear to operate in similar manner. It's when one looks deeper into the dynamics that it's realized there are significant differences that must be accounted for between the two.

    I still haven't seen an answer to the following question- has anyone ever seen or had experience with a boat that did not have active flight systems AND the foils did not extend beyond the maximum beam of the vessel? Inherent stability is the topic of concern.
     
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