link stringers to bulkhead or not

Discussion in 'Boat Design' started by Case Fabrications, Sep 5, 2022.

  1. fallguy
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    fallguy Senior Member

    Sorry. My interpretation was lacking. Mostly wondered about course of action.

    One of the really hard things during my build was QA and course of action. Very easy to say 'not right'. Very hard to decide action.
     
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  2. Ad Hoc
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    Ad Hoc Naval Architect

    As previously noted, if he is able to get a good cut without scoring the shell plate and adding 'notches', making it worse, he can do this:

    upload_2022-9-7_12-43-34.png

    Stop about 25mm short and snipe - simple.

    I think I may have designed the structure on this one (as I helped them out on a few of them)...so I can dig out the exact rules if you wish?
     
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  3. Ad Hoc
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    Ad Hoc Naval Architect

    Build and design is all about the QA...quality quality quality, and control and assurance of it.
     
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  4. Case Fabrications
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    Case Fabrications Junior Member

    I keep saying bulk head but I believe everyone is calling them frames. The whole reasoning for this post was whether or not to weld my longitudinal stringers to the frames where they are notched out to fit. The end does hit one of the main bulkheads for the first deck of course. Was just curious whether or not to link them together
     

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  5. bajansailor
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    bajansailor Marine Surveyor

    Ah ok, so your longitudinals are passing through notches in the frames, and not a (potentially watertight) bulkhead.
    However I am not too impressed by the single notch in way of the longitudinal in your first photo above - to say it is a bit rough is an understatement.
    And there is scope for more mouseholes in the second photo - or at least having corners with larger radiuses.
     
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  6. Ad Hoc
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    Ad Hoc Naval Architect

    AAAAaaahhh.. this is totally different from how I understood the initial post.
    You have slots, slots already cut into the deep frame (yes not a WTB). And you're wondering whether to weld them, since you have a cutout.

    Make a 100% differnce to the question!

    No..do not weld them...but as Bjansailor notes, the slots are terrible, sorry.
    If you can make them larger and smooth rounded corners will help 100%.

    If the slots are not like this, with weld rounded corners and enough space around them:
    upload_2022-9-7_13-34-47.png

    Then do not weld them...just make the slots, or cutouts better and less 'notched'.

    Terminology - is EVERYTHING, in ship/boat building!
     
    Last edited: Sep 7, 2022
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  7. Ad Hoc
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    Ad Hoc Naval Architect

    For ref:
    upload_2022-9-7_13-38-43.png

    You have no return for the weld around the web - that's a site of crack initiation.
    You have large craters at the ends of your welds - which implies too much heat as you stop - these are sites of cracking
    Your notch/cutout - has burrs and edges that are irregular - these are sites of cracking

    Just a few pointers too..
     
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  8. Case Fabrications
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    Case Fabrications Junior Member

    Are you telling me this CAD designed and CNC cut frames aren’t up to par? Gotta get a new engineering firm Hahaha. So I need to wrap my corners on the welds? Hold my trigger long on stops and clean up my work. I never though that jagged corners would matter but now that you mention it I can see how cracking could result
     

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  9. Case Fabrications
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    Case Fabrications Junior Member

    I have always been told when you wrap the corners with a small gauge material the heat effected area on both sides will crack directly above where the welds meet at the tip. My understanding and what I have been told my whole life is there are only certain places where you should weld on sides directly across from eachother. To avoid warping you go side to side starting your weld where the last one stopped. 1 weld length before the edge in a joint like that is preferred with smaller gauge material. Again, this is just what I have been told and my understanding was. Doesn’t mean I’m apposing they need to be wrapped, that was just always my perception. I do see though how where I stopped my weld I’m already too close to the tip not to though.
     
  10. Ad Hoc
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    Ad Hoc Naval Architect

    Well, let's look at the evidence:
    upload_2022-9-8_8-49-39.png

    The cutout has hard corners, if there is a small rad, it is way way too small. If those slots that are jagged were cut by CNC machine..then the speed of cutting is wayyyy too high.
    The depth of frame left above the cutout...is less than 1/2 depth. This is also poor. It should not be greater than 1/2 depth of frame.
    Not sure what those endless black sooty tack welds are doing at these critical locations too?

    Yes, this is how I spec the welds, like so:
    upload_2022-9-8_8-53-24.png

    We do a 75mm return around the cutout.


    No, the opposite basically.
    It appears that you 'suddenly' stop at the ends, hence the crater. That is, too much heat and a sudden stop which means not enough weld bead being deposited...so it effectively 'shrinks', creating the crater.
    You need to reduce the current gradually at the ends of the run..or try increasing the gun travel speed at the end - which effectively does the same thing, tapers off the heat applied at the ends, or add more weld-bead at these ends..
    you can do this by back stepping..or, depending upon the set you're using, some modern ones have functions that do this for you.

    Yup...and jagged edges on any metal, but especially aluminium - is a recipe for disaster awaiting to happen.
     
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  11. Ad Hoc
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    Ad Hoc Naval Architect

    Not sure i fully understand this.
    It just sounds like just poor prep for the weld...too much heat is being deposited and slow travel speed?
     
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