Welding the skin to the frames demystified

Discussion in 'Metal Boat Building' started by M&M Ovenden, Aug 31, 2008.

  1. welder/fitter
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    welder/fitter Senior Member

    Just a quick post to apologize to "drmiller100" for my childish post.
    Sorry, shouldn't have dumped my bad day on you.
    Mike
     
  2. Brent Swain
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    Brent Swain Member

    Welding skin to frames

    One would have to be quite naive to believe that a curved shape is no stronger than a flat surface, when it come to withstanding pressure.( Like believing a square propane bottle is just as good as a round one) This type of thinking keeps metal boatbuilding in the "Model T "era.
    You can squash a beer can flat without making a hole in it. Put in some bulkheads and it will tear a big hole in at each bulkhead, That is why frameless boats have far less chance of being holed on sharp rocks.
    Brent
     
  3. Guest62110524

    Guest62110524 Previous Member

    as usual you are so far off track
    your boat will be dumped on rocks beach even sandy beach, once it is pushed in so far, the deck will then push UP
    Visit a navy dock, see the ships with their close frames, dunno why I bothered answering you have been playing same worn out record for 4 years
     
  4. apex1

    apex1 Guest

    It is absolutely senseless Stu, we ask a blind to value colour. Gasbottle...........what a kind of comparison should that be?

    Brent.. some of us are adult! We do´nt fear the dark forest and know St. Claus personally! You´re stories do´nt gain truth if you repeat them another 5000 times.

    We have a sort of brother in kindred spirit in this religious repeated nonsense here in Germany. Herr Luft is calling all of us idiots, cos we have no clue how to build a metal boat. I wish him from the bottom of my heart once to get rescued by a German SAR boat. He will convert to a proper belief, be shure. Till then we can not stop them to spill their crap all over the amateur builder community.
    Kindest regards, and allways a proper framed boat under your back!
    Richard
     
  5. drmiller100
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    drmiller100 Junior Member

    hey, i'm a grown adult, out stirring the snakes with a stick. occasionally a snake is gonna take a swipe at me. No worries!!!!

    Mostly I'm trying to understand what the transverse frames actually DO.
     
  6. tazmann
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    tazmann Senior Member

    Take a look at some of the photo's on here and see the hull shapes,
    Now try to picture it in your mind trying to build em without transverse frames?
     
  7. drmiller100
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    drmiller100 Junior Member

    i've seen a fair number of 24 to 30 foot aluminum boats with no or only a very few transverse frames. To be fair, these are river boats designed to pound rapids and rocks, not the ocean. For the river boats, "everyone" knows you don't put lateral bracing anywhere near the bottom, because if you hit a rock the boat instantly STOPS when it hits a bulkhead hurting the passengers. Some boats do run lateral bracing just above the longtitudinal beams every so often.

    These boats also don't have "decks", only flooring. It seems like you could use the deck as a structural member, then use vertical braces to run the deck loads down to the longtitudinal beams.

    I doubt an ocean boat would immediately sink without transverse braces. What strength do the lateral braces add/??
     
  8. apex1

    apex1 Guest

    Have just a look at post # 109, one page back. You´ll easily imagine that such structure (no matter which material) has a enormous strength.Take away the members in one direction (no matter which), imagine again.
    Very much simplyfied, yes, nevertheless it´s valid. At least for heavy duty use. And in my opinion Cat. A always is heavy duty, sooner or later.

    Regards
    Richard
     
  9. Guest62110524

    Guest62110524 Previous Member

    take look at my website see frames,see complex shapes, you must also have frames to get these shapes, you can see more in my gallery
    Brent often says"well look at a pipe" but if you have a 12 foot dia pipe 4mm wall and you backed your car into it, you would leave a very crumpled pipe
    the sea is very hard medium, , try dropping off 30 foot vertical waves and see how an unframed boat fares
     
  10. MikeJohns
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    MikeJohns Senior Member

    Or try descending to 240 feet in that steel submarine with the transverses removed and you will have an empty toothpaste tube :) Then you see that transverse frames can provide a lot of strength.
     
  11. Brent Swain
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    Brent Swain Member

    Welding frames to skin

    The point is , building the complex shapes shown has absolutely no advantage over the shapes of origamiboats , not in performance , aesthetics , and certainly not in terms of construction or structural strength, so why do it, if your goal is to simply get out cruising and off the treadmill quickly and easily in a good looking , safe, well performing cruising boat? Throwing such hurdles in front of yourelf is totally counter productive. Efficiency can only be defined in terms of what you are trying to accomplish.
    The childish catcalls in the preceeding posts are totally meaningless, an admission that you have no real valid arguements to make.
    We are not talking about battleships here. They are not likely to sustain artillery shelling.
    As I mentioned many times, longitudinals along a curve are under compression, transverse frames are only under a bending load. What part of bending vs comprwession do you not understand? It would be far better for you to print this and read it for as many times as it takes to sink in,thru the ivory, however long that takes, than for me to have to keep posting it.
    Brent
     
  12. apex1

    apex1 Guest

    You are´nt to cure Brent, go build your ugly ducks, we go and build our tanks and battleships,
    Have good winds, calm seastates, sandy beaches and soft reefs

    Regards
    Richard
     
  13. welder/fitter
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    welder/fitter Senior Member

    Of course, this discussion of frames/no frames has gone on, seemingly, forever. In smaller boats, say under 40 feet, an important goal for building in steel would be to make it as light as possible. As the size of the boat grows, however, I'd be concerned about a lack of transverse framing. Though I know of people who are building 60 footers without transverse framing - and I hope that it works out for them - I have concerns over these builds, when in heavy sea states. Should I be proven wrong, I have no problem with admitting so. Still, I'd prefer to sink my money into the traditional methods of building and leave others to experiment with their hard-earned cash.
     
  14. MikeJohns
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    MikeJohns Senior Member

    I have pointed out before that the structural behavior is utterly predictable for a combination of pressure and point loads. We can tell accurately what the stresses will be, where the fatigue failures will occur and what factor of safety you have in reserve. Unless you have used these modern computer tools you cannot appreciate just how useful they are.

    Now that extensive data-acquisition has been collated on small sailboat loads Scantling societies are using FEA more extensively to fine tune their rules. GL and ISO give guides to the design of a "frameless" system and just what you can count as structural in way of chines curves etc.

    A collision that dents the plate has nothing to do with curves pre-stressing etc, it is principally and initially a local shear failure, once this dent has formed the remaining structure is immediately compromised unless there is sufficient support to prevent it collapsing. This is a big weakness with inadequate framing. Like the submarine pressure hull, the framing stops the plating from buckling and collapsing even if there is a non-critical localized yield from a collision or depth charge.

    Transverses also resist the vessel changing shape as it hogs sags and heels and makes the hull stiffer and much stronger as a girder. This is very evident in many larger GRP hulls with inadequate bulkheads as the hull wracks and distorts quite obviously while the vessels smaller sister-ship is quite rigid.

    When you get above a certain length, displacement, beam or righting moment then transverses of some description become a necessity. We cannot linearly scale the structure either e.g. from 26 feet to 60 using the same design. The loads increase disproportionately.

    In this era there’s no longer anything to prove by doing it blindly or with a miss-applied faith in a method since we can predict just what will happen to the hull with a given load.
     

  15. Ad Hoc
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    Ad Hoc Naval Architect

    I think in addition to Mike's comments one can also say the following:

    It is "theoretically" possible to make a vessel, say a large tanker, structurally frame-less. However the practicality will render it a failure. Such as being so heavy that it sinks - Requiring enormously thick shell plate to withstand all the global as well as localised loads.

    What frames do is act as additional load paths not just pure support. I read so many text books and technical papers that want to "optimise" the structure...as if it is some holy grail. I'm going to delve into my opinion on "optimisation" as it would require much more space that allowed here, but, suffice to say that a structure that has been optimised i can guarantee will eventually fail through some "load case" not considered or dismissed as not worthy.

    Frames provide the "safety factor" during any unforeseen loads in shirking the load to surrounding structure and allow the flow of shear to dissipate effectively and safely.

    Given a simple point load F, the supports experience a shear load of F/2, ie half. If that member connects to another that beam then has its supports at half of F/2, and if that is supported it too has half of that...and so on. So the more load paths, or frames that exist in the vessel, the more structurally reliable and safer it is under abnormal loads.

    And as Mike notes, when "scaling up" designs, the structure requires more attention and less assumption. Frames help in all situations...
     
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