a radical form of propulsion

Discussion in 'Multihulls' started by isvara, Nov 25, 2019.

  1. isvara
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    isvara New Member

    It occurred to me that if propellers were efficient then nature would have put them on at least some marine species.
    When hovering 3 metres above a 2 metre stingray whilst spearfishing some decades ago, I was startled and impressed with how it swiftly distanced itself from me with an undulating ballet like motion at the edge of its body. Upon returning home I cut a piece of thin plywood about 30cm x 30cm, tilted it about 15 degrees in the bath water and pressed down on it firmly with my hand roughly at its center of buoyancy. This obliged the ply to move quickly forwards following its enclined path of 15 degrees until it hit the bottom of the bath. at no time did it vary its tilt due to the comparatively large area. I theorize that if this fin was attached to a suitable vessel, moved mechanically up and down and reversing its tilt on the upstroke with a wave like motion then surely the vessel would move forward like a stingray. It should be very efficient.
    Has anyone ever done any such experiments? waddayarekon?
     
  2. Blueknarr
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    Blueknarr Senior Member

    The traditional gondola is propelled with that very movement. Although horizontally not vertically.

    Part of a propeller's mechanical efficiency is its continual rotation. It doesn't have a pause at the end of each stroke. Continual rotation is not biologically possible. Living organisms have to stick with reciprocal motions for propulsion. How many land animals roll on wheels?
     
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  3. Mr Efficiency
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    Mr Efficiency Senior Member

    I assumed he was taking about the wave-like motion of the outer flaps of the Ray.
     
  4. Tiny Turnip
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    Tiny Turnip Senior Member

  5. Tiny Turnip
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    Tiny Turnip Senior Member

    Here is a device using an undulating mechanism for propulsion:

     
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  6. Mr Efficiency
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    Mr Efficiency Senior Member

    Wow. I think the OP will agree that is the motion he was seeing with the ray
     
  7. gonzo
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    gonzo Senior Member

    That theory keeps on rearing its head. However, like paddle wheels, it is simply not as efficient as a propeller. Race boats, which can use any method to create thrust, do not use flaps. Please, do not bring up worldwide propulsion conspiracies. At this point in propulsion technology, improvements are minimal. Until someone ever comes up with a revolutionary system, we will have to live with the physical limitations of present technologies.
     
  8. TANSL
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    TANSL Senior Member

    Wise words.:)
     
  9. Mr Efficiency
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    Mr Efficiency Senior Member

    You are the only one doing that, that I can see.
     
  10. tspeer
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    tspeer Senior Member

    It's not quite the undulation of a stingray, more like the flapping of a manta ray. But the Hobie Mirage Drive oscillates in a biological manner instead of rotating.
     
  11. isvara
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    isvara New Member

    Thanks for the replys and video s. Never been close to a manta but sounds promising. A horizontal dagger board profile, maybe 2or 3ft long both pointing inwards from each hull and driven by a slow but powerful crank system would be an interesting experiment on a cruising cat. In stop position fins would be at top dead center and horizontal. Maybe drag would be a nuisance unless tilted vertically at rest.
     
  12. tspeer
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    tspeer Senior Member

    And then there's the Trampofoil.

    [​IMG]
    It has a foil that moves up and down, changing its incidence between the up stroke and the down stroke.
     
  13. BlueBell
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    BlueBell Ahhhhh...

    ...also known as the Exhauster!
     

  14. isvara
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    isvara New Member

    Many Thanks tspeer, it illustrates clearly how the alternating vertical force is multiplied to a horizontal direction.
     
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