Fish-tail / caudal fin human powered drive

Discussion in 'Boat Design' started by NeilG, Jan 14, 2014.

  1. NeilG
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    NeilG Junior Member

    I've seen a few designs for boats that are finned or sculled from the rear, but none seem to resemble how many fish power themselves.

    Fish seem* significantly more efficient in moving through the water than it looks to me like oars are, and I suspect with a couple of hundred million years of evolution to get it right, even give propellors a run for their money for energy efficiency. They can also turn around in less space and less time than probably anything on the water (except maybe a coracle).

    I suspect one of the most significant differences is the fact that they move a large part of their body into a curved surface, sometimes with a sine wave passing along their body - compared to only one flat surface moving in finned boats. This curve allows them to exploit rather than suffer from the creation of vortices as they move through the water
    (see https://www.google.com/search?q=fis...goG4BQ&ved=0CD4QsAQ&biw=1462&bih=774&dpr=0.75 )

    I'm working on a design for a human-powered fin-driven boat with a tail with several moving parts, so it can hopefully exploit the vortices in a similar way to how a fish does. I've created a dry mock-up (in meccano) for how this would work and I think it's got potential. I guess the next step is coming up with a wet working model.

    The fish (e.g. trout swimming has been studied) appear to make this work by having very sensitive pressure sensors along their side; they FEEL the tiny pressure changes in the vortices and shape their body accordingly. While this might be possible, clearly this isn't practical with a boat. However, there is presumably an optimum shape and frequency for maximum efficiency at a particular speed; they flex their body by different amounts and use a different cadence at different speeds and in different conditions. A boat could be designed around a suitable cruise speed and cadence that gives good efficiency travelling in a straight line - and while it might be relatively inefficient at other speeds or while turning, I don't see that as a big problem - the cruising speed is the focus.

    As a by-product, it could also create an extremely manoeuvrable craft.

    Are there any extant designs with a propelling tail that has more than one controlled, moving element? Any thoughts on this idea? Anyone interested in being involved in this design? If there's much interest an open source project for fish-like finned propulsion could be set up.


    (* I don't have any direct figures to compare rowing with fish; this is an instinctive judgement, but rowing LOOKS a very inefficient method of locomotion to me.)
     
  2. Jeremy Harris
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    Jeremy Harris Senior Member

    Buried deep with the human powered boat thread there is some data on the relative efficiency of rowing versus other forms over human powered propulsion, and, I think, there is some data on fin-type systems.

    IIRC, rowing can get to around 50% or so efficiency, the fin drives that have been reasonably well assessed are a little worse by a few percent. Propellers and large diameter paddle wheels are generally regarded as about the most efficient drives. A properly designed propeller for a human powered boat can run at around 80 to 85% efficiency, but may present problems in terms of the depth of water needed to accommodate the large diameter needed. Large diameter paddle wheels can be around the same efficiency, and work in shallower water, but the large diameter needed creates practical problems, like windage and obstruction either side of the hull.

    Finally, a very large diameter air prop (as used on Decavitator, for example), can be as efficient as a good water prop.
     
  3. Squidly-Diddly
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    Squidly-Diddly Senior Member

    I'd like a kayak rudder with long enough 'tail' and slick enough action to allow it to at least maneuver with feet only when fishing.

    Should be able to control both speed and direction with just feet.
     
  4. portacruise
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    portacruise Senior Member

    http://en.wikipedia.org/wiki/RoboTuna

    http://siliconangle.com/blog/2012/0...-on-drugs-sinks-to-new-depths-with-robo-tuna/

    http://books.nap.edu/openbook.php?record_id=5870&page=946

    Hope this helps,

    Porta


     
  5. NeilG
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    NeilG Junior Member

    Thanks; I've browsed quite a few pages of that thread but it sounds like it's worth my time going through the whole thing.

    Interesting; I imagine it's a lot more vulnerable to extreme weather conditions though.
     
  6. NeilG
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    NeilG Junior Member

    There's a lot to be said to having hands-free for other tasks. My current design would use hands and feet, BUT the hand controls could be locked-off and the larger fin just driven using the feet (both for drive and for steering) - however using hands AND feet together would allow greatest manoeuvrability and the best chance of maximum efficiency. I'll see if I can get it into a clear sketch form (not my forté) or photographs to illustrate what I mean.
     
  7. NeilG
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    NeilG Junior Member

  8. portacruise
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    portacruise Senior Member

    Hi, Squidly,

    I'm a fisherman also and understand about the importance of "hands free". There are several approaches to this though only a few might work with a kayak. Rudders are essentially useless for control in the types of fishing I do.

    Some ideas of two hands free craft:
    Float tube fins with a pontoon/float tube allow for precise control (primary propulsion by motor) but can't match the speed of a kayak. Toon/tube can quickly/easily turn within its own length to face a running fish. http://www.flyonly.info/floattube.html
    Seacycle uses a seat lean mechanism for steering and back/forward pedalling for position control that is not as precise.
    Note the hinged pontoons: http://www.castlecraft.com/water_bike.htm
    Various mechanical cable and or control rod linkages as well as wireless remote control used with troll motors adapted from bass boats to kayaks and small boats....

    Hope this helps.

    Porta


     

  9. NeilG
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    NeilG Junior Member

    Further research might get me to rethink/abandon this design. According to http://www.bluefish.org/jettuna.htm, around 80% of the thrust of the most efficient fish is produced by the movements of their BODY, not by their tail. I can't currently envisage a practical material/structure for a boat that would allow a large proportion of the boat to fluidly change shape (and even if there was a way, I don't think I'd trust the reliability of that many essential moving parts on a boat either. Plus, the construction would be far more complex and costly).

    So, looks like it's probably a pedalled propeller for my possible project then ...
     
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