Directional Stability Problem in Towed Barge

Discussion in 'Hydrodynamics and Aerodynamics' started by conceptia, May 22, 2012.

  1. conceptia
    Joined: Nov 2009
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    conceptia Naval Architect

    Recently we noticed that one of our crane barges are fishtailing while being towed by Tugboat. We are using a bridle rig, since the barge is fuller at the fwd end. Can anyone suggest what could be the reason for this? For me, I believe it is something with the towing arrangement as we had a calm and clear weather.
     
  2. gonzo
    Joined: Aug 2002
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    gonzo Senior Member

    Do you mean that the barge is more loaded at the forward end? Ideally it would be level or dragging a bit at the aft end. That makes it be more stable while towing.
     
  3. Poi
    Joined: Apr 2012
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    Poi New Member

    A skeg would help.
     
  4. tunnels

    tunnels Previous Member

    if its something thats happened recently then what are you doing differantly ??
    loading has everything to do with the way it will tow !! heavy at the front and yes it wasnt to bow steer and wag its tail , its common sense !!
    Also the speed of the tow !! is it being towed Faster than before ??
    What about the length of the towing bridle ??
    The towing vessel could be causing it with the wash from the propeller !!
    Load it slightly tail heavy !!
    As i said whats changed ???something has but what ???? :confused:
     
  5. HakimKlunker
    Joined: Aug 2009
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    Location: Thailand

    HakimKlunker Andreas der Juengere

    If this is not because of sea conditions (wind direction, current) I would first look into towing conditions.
    If the bridle itself is very short, you will have more yawing than with a longer one.
    To shorten one leg of the bridle by a fraction will perhaps stabilize to some degree - but with the cost of a little more towing energy required.
    A very flat bottom increases the yawing tendency, and the mentioned skeg may help.
    Not sure of you can trim the barge aft but this certainly will help, too.

    You said "ONE" of our barges... this means that you have more of them and they do not have this 'problem'? Then you can investigate where the naugthy one is different.
     
  6. philSweet
    Joined: May 2008
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    Location: Beaufort, SC and H'ville, NC

    philSweet Senior Member

    If the center of gravity of the barge is aft of the center of resistance of the barge's hull, then once it starts to sway it will tend to continue (same as a U-Haul trailer does on the highway if aft loaded). Even so, barges tend to be pretty well damped. A second problem could be coupling between pitch, yaw and roll. This happens when the moment of inertial in pitch, say, is exactly twice the moment of inertia in roll. Or it could be roll and yaw. Those problems are quite a bit harder to sort out and would most likely require the help of a pro. Neither will respond to fiddling with the bridle.

    What do you mean by fuller at the bow? More heavily loaded and deeper draft? that could shift the resistance way forward as waves build up. Is there a speed where this suddenly starts?

    I suspect that it is an inertial coupling problem that happens to have a sweet spot at your tow speed. The bridge tenders must just love to see you coming:D

    Let us know how it plays out.
     
  7. Yobarnacle
    Joined: Nov 2011
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    Yobarnacle Senior Member holding true course

    If the barge is deeper in the bow, she'll "root" or "hunt", same thing, different names for it. She'll yaw back and forth on tow. Adjust trim so stern drags about half meter deeper. Otherwise, if it's a multiple tow, hang another towed piece of equipment behind her stern to steady her.
    Final solution if nothing else can be done, and hunting can not be tolerated, shift one bridle leg to a different attachment point. Wider, or narower. Towing slightly offcenter, will change hunting, to a bias to run to one side. Good luck.

    One other tactic. Re-rig bridles to opposite end, and tow stern first. :) Don't forget to shift running lights, if you do.
     
  8. HakimKlunker
    Joined: Aug 2009
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    HakimKlunker Andreas der Juengere

    This makes you and me 'non-pros' :p (see above)
     
  9. Yobarnacle
    Joined: Nov 2011
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    Yobarnacle Senior Member holding true course

    Yep. Cap.
    I'm just a stupid old retired tug driver. 43 years at sea. :D
     
  10. daiquiri
    Joined: May 2004
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    Location: Italy (Garda Lake) and Croatia (Istria)

    daiquiri Engineering and Design

    Conceptia, can you give us barge dimensions, displacement and the towing speed?
     
  11. HakimKlunker
    Joined: Aug 2009
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    HakimKlunker Andreas der Juengere

    A picture may help as well. That makes the term 'barge' clearer. Some people may have different opinions of what a barque is?
     

  12. TeddyDiver
    Joined: Dec 2007
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    TeddyDiver Gollywobbler

    And there are lot of different types of barges too
     
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