Chinese river ship launch failure

Discussion in 'All Things Boats & Boating' started by Brian@BNE, Oct 14, 2011.

  1. philSweet
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    philSweet Senior Member

    The part that had me scratching my head is that the bags can be persuaded to roll straight and not squeeze out one side or exert large cornering forces or pile up on one another. The skins have to be stretchy enough the deform around keels and bilges without wrinkling; but this causes problems because even though the air pressure is the same everywhere, The tension on the skin will be different in girth and length at different points on the bag (girth tension is twice length tension only for a circular cylinder, not for a flattened one), hence the circumferance varies. Now as long as the top flat and bottom flat are similar, I guess it doesn't matter because the bag will travel half as fast as the boat no matter the circumference. So a bit of lean left or right won't matter much. But if the shape of the top and bottom is different there are bound to be problems. One thing this isn't is a rough terrain launch system. I'm pretty sure that the flatter the bag ends up, the less turning force is produced by bump or lean. It looks like if you start with 1 PSIG and flatten the whole bag with a flat load you end up at about half the original height for the four ply bag and about 0.4 height for the six ply bag at rated pressure. A bit lower if the ends of the bag poked out.
     
  2. gonzo
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    gonzo Senior Member

    $2.6M what? I can't believe that boat cost that in US dollars.
     
  3. powerabout
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    powerabout Senior Member

    ah yes China
    $20m boat only $2.6m to recover it for the local government
    must have been a mistake in the translation in the newspaper
     
  4. RayThackeray
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    RayThackeray Senior Member

    Bad launching

    I saw the sinking coming in the first few seconds of the video. Assuming the design waterline was good, the launching would have gone fine if done sideways or even bows first. What I saw in this case was downflooding over the transom because of the launch angle. From this video we don't yet have any real reason to suppose the design is bad.
     
  5. Poida
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    Poida Senior Member

    Impressive calculations Angel, however do the normal calculations for rolling apply here?

    The rolling characteristics here are the same as the rolling nature of the molecule in grease of the synovial fluid in a human joint.

    The airbags are reducing the friction between the ship and the ramp by the rolling of the air molocules within the bag.

    I don't really understand what all this means.

    I think I'll have another beer.

    Poida
     
  6. Angélique
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    Angélique aka Angel (only by name)

    [​IMG] Angel
     
  7. daiquiri
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    daiquiri Engineering and Design

    But I was not judging the design at all. Just the methodology of the launch, which obviously has been calculated and performed very, very badly.
     
  8. Angélique
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    Angélique aka Angel (only by name)

    On second thoughts I think those bangs are firecrackers as they go on after the ship is in completely in the water.

    4:32 till 5:38 in the vid seems to be a perfect launch to me.

    Cheers,
    Angel
     
  9. kach22i
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    kach22i Architect

  10. Angélique
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    Angélique aka Angel (only by name)

    All the airbag launched ships I've seen in this thread so far in pics, vids and links are flat or almost flat bottomed.

    Cheers,
    Angel
     
  11. Angélique
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    Angélique aka Angel (only by name)

    That was my first question in post#5... ‘‘ But in this case, launch ramp to steep or bad boat or both . . ? ? ’’

    Maybe we sould send them an e-mail for relaunch to attach some of those launch airbags along the hull starting at the end that launch first, bow and transom seems about equal height, not sure freeboard is high enough for sideways launch...

    Cheers,
    Angel
     
    Last edited: Oct 17, 2011
  12. Angélique
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    Angélique aka Angel (only by name)

    But, on second thoughts, that would only support the ends of the ship during mid launch. One end supported by shore (that doesn't supply enough surface for rolling airbag support) and the other end supported by the attached floating airbags.

    So maybe best to get a dozer to lengthen the ramp to reduce the angle, smooth it out and firm the soil, that will do as bottom pressure will be max 1.2 kg/cm².

    Last time I saw a ship in the news only supported by its ends it broke, but that was a laden barge...

    Cheers,
    Angel
     
  13. Angélique
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    Angélique aka Angel (only by name)

    Digged it up, story is the bow hit a shore (rudder failure?) then the current pulled the ship across the river so it got stuck between both shores, then the tide went out.....

    September 14, 2011
    [​IMG]

    Pic source / translation, there is also a vid, no sound so no translation :p


    [​IMG]

    Pic source / translation.


    Ship is on the Hunte NE of Oldenburg.

    [​IMG]

    Cheers,
    Angel
     
  14. coolmike
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    coolmike Engineering and Design

    I agree with you. The problem of this launch accident is the launch only. Obviously the launch ramp is not paved and too steep. From the official report we knew that airbags didn't roll with boat as they got stuck in mud. It is a shame of airbag launch, I have to say, ever I saw many crazy stupid launching.
     

  15. coolmike
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    coolmike Engineering and Design

    Yes, firecrackers. Most Chinese shipyards will celebrate launching with firecrackers.
     
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