Distorted deck plating

Discussion in 'Metal Boat Building' started by spaceboy, Aug 28, 2018.

  1. SamSam
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    SamSam Senior Member

    So, is there a practical solution to a deck like this? Total replacement sounds overboard, so to speak.
    Using a regular cutting torch (without using the cutting lever) to do a bunch of dots spiraled over the affected areas, or putting it on a simple wheeled holder and running lines should be simple. How hard can it be? It's easy to see the difference between bright red and dull red. There are all kinds of articles about flame straightening steel plate and if the only other 'solution' is wholesale replacement, what is there to lose by trying? The claim that it takes vast levels of experience sounds dubious to me. Even if heat flattening only goes so far, there has got to be some kind of trowelable 'leveler' composition of some kind for steel ship decks that would take it the rest of the way towards being acceptably flat.
     
  2. gonzo
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    gonzo Senior Member

    I think it could be improved by cutting the flange on the deck beams every few inches, jacking up the deck and re-welding. The longitudinal welds at the deck plating may have to be partially cut too. I
     
  3. Ad Hoc
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    Ad Hoc Naval Architect

    That is all out-of-plane and only effects the stiffness of the beam, not the plate and its associated distortion.
     
  4. gonzo
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    gonzo Senior Member

    Jacking up the deck will get it in-plane; or rather make the crown more fair.
     
  5. JamesG123
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    JamesG123 Senior Member

    That isn't the problem.
     
  6. MikeJohns
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    MikeJohns Senior Member

    Line heating is very time consuming and a high level of expertise is required to get a decent result on thin plating. It's not easy and I think its not sensible for the bulk of the work. With thinner steel plate you also need to quench one side continuously while heating the other.

    As I posted on the first page I've seen worse than this corrected quickly by simply cutting and welding, both frames and plating. Adding the caveat that the usual rules for welding apply.

    Smaller steel craft don't require the decks for global strength beyond a narrow deck shelf. Fabricators can do all manner of remedial techniques on small steel craft that would not be allowed on larger vessels.
     
    Last edited: Sep 4, 2018
  7. Ad Hoc
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    Ad Hoc Naval Architect

    This:

    has nothing to do with:

    nor being out-of-plane.

    Do you understand what is out-of-plane?
     
  8. SamSam
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    SamSam Senior Member

    OK, forget about flame straightening (I'd try it) but out of curiosity, is there some kind of filler/leveler that is used in shipyards on exterior steel decks to make them extra flat for a paint finish?
     
  9. MikeJohns
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    MikeJohns Senior Member

    Some filling with epoxy fillers by the painters but no bulk filling. Building contracts usually specify an acceptable level of fairness. Anything like the OP's vessel would be rejected.
     
  10. spaceboy
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    spaceboy Junior Member

    Thanks for all the answers guys, I think there is a consensus that hot work is not a suitable method for this job. Do any agree that the transverse butt welds should be cut first to see if the plates spring back? If not, then continue with removing the deck beam welds starting nearest the cut welds.
     
  11. JamesG123
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    JamesG123 Senior Member

    They might not. If everything, plates & beams have settled in relative to each other and the (current) hull shape. But yeah, cutting first at the "edges" well let you see if there were any gross tension on the structure the deck was responsible for. Then cut the beam welds to release them and see what happens. But I doubt that the deck plate(s) are going to go back to any shape that is useable. You should have cameras recording when you do it.

    How old is this boat? Do you know when the deck was welded down?
     
  12. Ad Hoc
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    Ad Hoc Naval Architect

    It is hard to say 100% because seeing in person is much easier to give better guidance.
    However, if you cut the trans butts, the locked in residual stress may go pop, which is great, but it may also make the free edges distort even more as it takes up its own shape and being influenced by the surrounding stiffer structure. And then you may have an even worse job on your hands, since you'll be doing the same as before, forcing the plates into place. This is ok if you have small patches, but the pictures look excessive!

    I would removed the frame web to deck plate welds, let the deck plate take its own shape. And assuming the frame webs are all correct and don't move (or much), then you can use the frame webs as your template to cut and shape the deck as required. It is much easier to cut and shape the plate once the stiffness from the frames have been removed.
     
  13. SamSam
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    SamSam Senior Member

    Thanks. Yes, until a person got used to it the deck would be a trip hazard.
    How far apart are the deck beams? Is the level outside on the deck in the photos transverse or lengthwise to the boat?
     
  14. gonzo
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    gonzo Senior Member

    I'm not going to argue semantics with you. I can make that deck look reasonably well with the method I posted.
     

  15. Ad Hoc
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    Ad Hoc Naval Architect

    Nothing to do with semantics.
    It is your statement that is in question, which you can either explain or not explain.
    If you elect to throw in replies like they are going out of fashion, merely to post, that's fine, that's your prerogative. But it doesn't make them correct.

    Jacking up, is not the same as cutting flange welds.
     
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