What do you think about this hydrofoil?

Discussion in 'Hydrodynamics and Aerodynamics' started by MantaRay, Mar 9, 2013.

  1. MantaRay
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    MantaRay Junior Member

    Brand spanking new to this forum. Such great wisdom and info here.

    I have had a growing interest in hydrofoil boats in which I have looked through lots of concept designs too. I stumbled across this submerged design and it seems to me this could create very good lift due to the large surface area of the wing (perhaps it could work better if wider?). I have not seen any practical hydrofoils that employ this lengthy wing. Either it has not been tested before, it is not efficient, or it causes problems.

    ..
     

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  2. Submarine Tom

    Submarine Tom Previous Member

    Welcome Manta,

    Terrible design on that hydro unless you've got lots of power.

    But, then it could be interesting.

    It looks like a model.

    There aren't too many fans of them here but a few die-hards.

    I'm sure you'll be hearing from Doug Lord soon...
     
  3. PAR
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    PAR Yacht Designer/Builder

    A design like this will need huge power requirements, just to get up on the foil and then huge amounts of power, compared to a more conventional approach to maintain flying the foil. Obviously done by someone that hasn't performed the math yet. The prop pods look like they might be electric, which means they really haven't done the math yet.
     
  4. MikeJohns
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    MikeJohns Senior Member

    As Tom said simply terrible: Looks like a cross between a very badly designed ground effect craft and a very poorly matched hydrofoil.
    And as PAR said no ones done any basic math yet, just sketched a fantasy craft.
    The thrust from those air props might move it at 5 knots. But more importantly there is an abysmal lack of buoyancy fwd and a very effective diving plane.
     
    Last edited: Mar 11, 2013
  5. PAR
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    PAR Yacht Designer/Builder

    5 knots is a bit optimistic, don't you think?
     
  6. MantaRay
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    MantaRay Junior Member

    Thanks for the replies guys.

    Regarding the aero/hydrofoil combo, I stumbled across this design (AIRO) which actually has practicality, although sail powered.

    [​IMG]

    Although I am wondering how effective the aerofoil would have considering power of hydrofoil.
     
  7. daiquiri
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    daiquiri Engineering and Design

    Your doubts are legitimate.
    It will have almost no effect, for at least two reasons:
    1) That hull, as shown in the picture, is a very inefficient lifting body, It would require angles of attack of more than 25-30 degrees to produce any sensible lift.
    2) The ground effect requires a close proximity to the surface, but the hydrofoils will tend to lift the hull up and away from the surface, thus cancelling out any contribution of the hull to the overall lift

    Cheers
     
  8. MantaRay
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    MantaRay Junior Member

    Would I be correct in saying that hydrofoils are more 'powerful' than aerofoils due to the higher density of water compared to air? More particles acting on the foil equals more pressure difference therefore lift. I suppose that is why the wings of aerofoils are larger to that of hydrofoils - aerofoils need to capture enough fluid particles to create lift. Forgive my technical ignorance, I am working on it.

    I think the only time a hydro/aero combo could be of use is before WIG crafts take off from water. Using hydrofoils they can reach the speed required for the aerofoils to become effective faster, then when the craft becomes air-borne the hydrofoils can contract into the hull. Of course the hydrofoils cannot lift the hull out of the water too far. Just a theory..
     
  9. Submarine Tom

    Submarine Tom Previous Member

    Ground effect can be of good benefit as velocity increases which is what happens with well designed hydrofoils.
     
  10. daiquiri
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    daiquiri Engineering and Design

    That is correct.
    This is not. :)
    If you take two geometrically similar airfoils (hence, the only difference is their relative scale) and let them run at the same angle of attack, the same Reynolds number (which is given by density*speed*length/viscosity, but one in the air and the other in the water, the pressure field around the two will look the same. And so will be the pressure difference. So the relative difference in lift produced comes from just the density.

    Cheers
     
  11. Doug Lord
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    Doug Lord Flight Ready

    Take a look at this paper-it answers a lot of questions about the premier small sailing hydrofoil, the Moth:
     

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  12. MantaRay
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    MantaRay Junior Member

    I had found this funky looking thing and it reminded me of what I wrote here.

    [​IMG]

    [​IMG]

    Apparently it is actually in development (for 2025) so it is not just a concept. Both aero and hydro foils going on there. I wonder if the hydrofoil become a stabilizer aerofoil when the ship becomes airborne.
     
  13. daiquiri
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    daiquiri Engineering and Design

    Come on, Manta. Don't swallow these marketing baits so easily.
    That thing will fly only when an anti-gravity drive is invented.
     
  14. MantaRay
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    MantaRay Junior Member

    Damn, it would have been pretty cool to see something from Star Trek on the waters.
     

  15. SURFFOILS
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    SURFFOILS Junior Member

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