Speed/Length ratio and barge trains

Discussion in 'Hydrodynamics and Aerodynamics' started by Michael Y, Jan 28, 2014.

  1. Michael Y
    Joined: Oct 2010
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    Location: Pennsylvania

    Michael Y Junior Member

    Is the speed/length ratio of a barge train with pusher related to the length of the total ensemble, pusher, or individual barges?

    Seems to make sense it'd be the total ensemble at first glance. If so, what is the max distance between barges you can tolerate before it breaks down? Issues with flexible coupling between barges?

    Did some googling, but not finding any reports in this realm. I know someone has looked at it somewhere.
     
  2. NavalSArtichoke
    Joined: Oct 2013
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    NavalSArtichoke Senior Member

    If the towboat and barges are lashed together, the S/L ratio is based on the total length of the tow. If the towboat is towing the barge or barges behind on a towline, you would look at the length of the individual vessels to calculate the S/L ratio.

    Most tows travel at really low S/L ratios, so I'm not sure where this is going.
     
  3. BMcF
    Joined: Mar 2007
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    BMcF Senior Member

    NSWCCD conducted some research on "sea train" concepts a few years ago that did include even some that were not physically coupled. I believe that they did publish some of their results in the public domain; if I recall correctly, one of the authors and principle investigators was Gabor Karafiath. That might help your google search whilst I find time to dig in my archives. We also conducted tests with a multi-segment sea train "barge" concept, but the barges were supported by an air cushion. The beneficial effect of the decrease in speed/length ratio with more and more segments would certainly apply to displacement barges too...but differently at different speeds than any of the work we did. All of our work was focused on speeds above 35 knots.

    As for anything that specifically deals with the "gap effects" in such a train, I'd have tp go back and look for that. I know we did not even consider that variable in our work; the segments were as closely coupled as we could manage to make them..effectively continuous along the keels.
     
  4. Michael Y
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    Michael Y Junior Member

    Thanks for the google tipper. Found some of what I was looking for.
     
  5. DCockey
    Joined: Oct 2009
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    DCockey Senior Member

    Usually speed/length ratio is of interest for use in estimating wave resistance, or at least the speed above which wave resistance is significant. Michlet can model the wave resistance of multi-hull vessels and might provide insight into the question of the effects of gaps between vessels on wave resistance.
    Michlet: http://www.cyberiad.net/michlet.htm
     
  6. Michael Y
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    Michael Y Junior Member

    I am curious of the impact of vessels "flying in formation" nose to tail, and if when they get close enough the speed/length ratio is of the ensemble, so they can realize a speed gain or powering reduction. Different physics, but analogous to drafting with cars and bikes or formation flying with birds.

    Obvious issues with floating things running into each other, but one problem at a time. :)
     
  7. ancient kayaker
    Joined: Aug 2006
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    ancient kayaker aka Terry Haines

    Tail-gating to reduce friction is common in motor and bicycle racing: why not check out watercraft racing to see if the technique is used? I somehow doubt it due to turbulent wake effect but . . .
     
  8. johnhazel
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    Location: Michigan

    johnhazel Senior Member

  9. johnhazel
    Joined: Jun 2008
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    Location: Michigan

    johnhazel Senior Member

    I race North American Marathon canoes. 5.64m long, 350-400Kg, 3m/s. 3m^2 wetted.

    We draft bow-stern and find that closest is best. This is not optimum traqnsverse wave surfing posion. Apparently, the best assist from the transverse wave is not as great as the greatest reduction in skin friction drag.

    We also "side wake" i.e. surf the divergent waves.

    http://marciarimer.smugmug.com/Cano...74896_MCWqJJ#!i=1284065523&k=HqbCNvj&lb=1&s=A
     
  10. Leo Lazauskas
    Joined: Jan 2002
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    Location: Adelaide, South Australia

    Leo Lazauskas Senior Member

    I can entice ducks to do something similar. :)

    If you throw bread in the right place near, but not too near, a couple of
    ducks, one will take the lead, and another will stay on its bow wave
    (presumably saving a bit of drag). When close to the bread, both ducks
    make a final lunge. I haven't compiled stats (I'm not quite that sad) but they
    both seem to have an equal chance at the end of the "race".

    I found a good title for a short paper ("The Differential Games
    That Ducks Play") but I never managed to get any further. I'm sure a
    student (equipped with Michlet, some stale bread and a duck pond) could
    have fun with something like that.
     

  11. johnhazel
    Joined: Jun 2008
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    Location: Michigan

    johnhazel Senior Member

    I've seen that! :)

    BTW our boats are actually 160-180Kg (350-400lbs)
     
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