Submarine driven by kites

Discussion in 'Boat Design' started by schakel, Feb 1, 2016.

  1. bpw
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    bpw Senior Member

    I think the basic point is being missed, does a submarine actually have less drag than a foiling boat? Seems very unlikely to me but I know very little about submerged objects.
     
  2. schakel
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    schakel environmental project Msc

    It's completely something else.
    The forces this torpedo underwater can pull is much greater then any foiler will ever do, therefore more propelling power.
    More lateral forces gives more forwarding power is the idea. Less instabilty from waves.
    How much was the drag on vesta's sailrocket? Current record holder.
    Far under 1.5 ton.. ? Don't think so. Area of vesta's sailrocket wing= 22 sqr m.
    [​IMG]
    And to my astounishment I see the record is on 65,54 knots, not 50 knots.
    And remind you.. Vesta's sailrocket is not a foiler.
     
  3. Squidly-Diddly
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    Squidly-Diddly Senior Member

    Makes sense to eliminate as much surface intersection hull drag as possible, and even above water air drag on non-sail parts of the boat.

    And foils need to be at least a LITTLE bit under water to work well.

    But I think you'd do better with above surface foil supported craft if you need to transport any VOLUME, since the volume will only be cutting through air, not water.

    Sub-kite would be ideal for transporting Uranium, if the kite also provided buoyancy for starts and stops.
     
  4. schakel
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    schakel environmental project Msc

    Same discussion as post number 10 of this thread:

    It makes sense to provide as much lateral forces as possible.
    Underwater gives more grip. therefore more propelling power.

    And the uranium transportation is for fun. I know.
     
  5. MikeJohns
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    MikeJohns Senior Member

    Ras

    Military subs have often been unable to adjust static trim above 200 feet in sustained storm conditions because they pitch and roll too much. The effect is much worse in water shallower than one half wavelength. The orbitals are of significantly greater amplitude at greater depths from the sea floors effect.
     
  6. MikeJohns
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    MikeJohns Senior Member


    It's not a feasible concept for a speed record.

    If the submersed body is not deeply immersed it still has a significant wake and associated drag even similar to a displacement surface craft. The more it’s shaped for efficient submersed running the more of the wake it produces near the surface.

    To avoid wave drag you need a long cable. Long tow cable drag even in turbulent flow regime (say >20 knots) is going to be the dominant drag in a towed system. And that's the immediately obvious Achilles heel. If it's shallow it's still a surface vessel, if it's deep the towline drag is crippling.

    You might be interested that taut cables have many resonant modes and they tend to thrum at several frequencies in water and that further significantly increases their resistance.

    There are other drag issues you haven’t considered. Depth control is necessarily dynamic using lifting foils with lift to oppose the upward pull of the towline. That’s also a significant drag.

    I'm not even going to start on the reality of Submarine design issues. The drag regime immediately makes the concept a farce for a surface towed submersed system.

    The only speed record you will achieve will be that for a submersible towed by a kite. Certainly it could never even enter the ballpark that an ultralight surface skimming craft can attain.
     
  7. Rastapop
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    Rastapop Naval Architect

    I believe you. Wavelengths long enough for that aren't uncommon.


    I may be misunderstanding you, but I hope you're not saying the effect of waves has a positive correlation with depth?
     
  8. MikeJohns
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    MikeJohns Senior Member

    Rastop
    Never believe anything, validate it :)

    I guess I didn't explain that very clearly. The Orbitals are more significant at greater depths in shallower water that in deep water. Here's an illustration:
     

    Attached Files:

  9. Rastapop
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    Rastapop Naval Architect

    I believe you because I already knew it - it's even been discussed in this thread already ;)

    Those images don't show that at all (the two images have no relationship to each other).
    The second image simply shows that at depths less than half the wavelength the bottom will distort the orbitals into ellipses.

    You can see the images in context here: http://www.pilebuckinternational.com/chapter-4-waves/
     
  10. MikeJohns
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    MikeJohns Senior Member

    Thanks
    I'm confusing the greater surge effect from the flattening eliptical orbits. I just remembered the orbit was of a higher amplitude but it's greater in the horizontal and lower in the vertical. It's the effect that rolls the sub more violently that's sitting on the bottom in shallower water that at the same depth in deep water.
     

  11. daiquiri
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    daiquiri Engineering and Design

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