Welding the skin to the frames demystified

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

  1. Ad Hoc
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    Ad Hoc Naval Architect

    welder/fitter

    1) what do you mean by "outboard edges"..?
    2) What do you mena by "over lap"

    I have an idea what you are saying..but i need to be sure exactly what you mean, before i reply
     
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  2. welder/fitter
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    welder/fitter Senior Member

    Outboard edges would be the edges of the transverse frames which are closest to the shell plating.

    Overlap - the amount of interface between the frames & longs. Some builders lay their longs as far into the slots in the frames as is possible, tack them well, then plate. I think that Wynand is suggesting that this is a mistake, that he prefers light tacks that can be broken easily enough to relieve the plate, once the plate is welded, or perhaps, tacked well. Like most members, I have a great appreciation for Wynand's finished products. Why create a hull that you have to fair, if it is avoidable. I have found that rounding the outer edges of the frames, if they are to be a close fit to the plate, allows the plate to ride across more easily. As well, when frame edges are not radiused, the plating in contact with the frames tends to show the placement of the frames, vertical hard points, if you will. With barges, freighters, etc., this is of no concern & a great benefit to the shipfitter whom is tasked with repairing the plating, as he can run his soapstone across the surface of the plate and find the frames. Obviously, I'm talking about non-floating frames. On a smaller boat, where lighter materials are used & aesthetics are more important, I use a similar method to what Whoosh suggested, placing wire between the frame edge & plate surface, prior to tack-welding. I use a 3/32 rod, but same concept. It is pretty difficult to agree on how much welding of components to the inside of the shell plate is required, as material thicknesses, & degree of surface contact, as well as intended use/application, are variable. I think that Murielle's suggestion of weld spacing & size are pretty standard. I can't remember who mentioned the Sika products, but I concur that sikaflex is a great product for filler. Laid in correctly, it is the perfect moisture barrier. In a recent commercial ferry build, we threw out the sealer that was supplied with the windows & used sikaflex, as we've had great luck with it in many previous refits. It doesn't seem to dry-out , crumble & crack, the way the old stuff used to.

    Mike
     
  3. Ad Hoc
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    Ad Hoc Naval Architect

    welder/fitter

    Hmmm..it is the same old same old...different people using different terminology for the same thing.

    1) "...edges of the transverse frames which are closest to the shell plating..."
    A transverse frame has two edges, one facing fwd and one facing aft, but both 'are touching the plate. So I'm sorry, but still not clear with what you are explaining, since both edges are in contact, that is the fwd edge, facing fwd and the aft edge of the transverse, facing aft.

    2) I think i understand you, but again some of this is down to the sequence you use.
    All plating should be fully welded prior to any long.ts or frames being fully welded, since the plate must be unstressed when major structural members are attached. If you weld these first, you'll get cracking from the restraint of the frames as these are stiffer. These members should be just tack welded.
    The long.t stiffener, lets say this is 100mmm deep. Lets say the transverse frames is 300mm deep. the overlap, or cross over, as i understand what you are saying, is down to class rules. The minimum cross over, ie the amount of weld in each direction is the smallest members depth x1.75. So in this example, a weld of 100x1.75 = 175mm, would need to be deposited either side of the intersection, fore/aft and transversely.
    If you're not welding to class you can do as you like. But, the main transverse frame carries the load....so if this is not attached to the shell and longts. correctly, ie overlaps in both directions at intersections, then you're asking for trouble later on.
     
  4. Wynand N
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    Wynand N Retired Steelboatbuilder

    Sorry for the delay in reply Mike. Yes we take off the sharp edges of the frames (bevel) but do not grind it totally round. Taking the sharp corners/edges off helps the paint/epoxy to stick better and get an even coat on there - paint does not like sharp corners.

    The overlap however is purely up to the detail in the drawings and designer specified. However, in my own steel designs I allow for a minimum of 60% of stringer to overlap the frame on floating frame design.
    For normal frame to hull weld method the complete stringer slots into the frame.
     
  5. welder/fitter
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    welder/fitter Senior Member

    Thanks, Wynand. As I have probably mentioned in the past, I'm planning a future build on a multi-chine Hankinson design. As my daily work is on commercial marine vessels - barges, freighters, ferries, etc. - no time is spent on making hulls more than structurally sound. Though I have built a couple of fishing boats and have been involved in the building or repair of a handful of sailboats, I am always reading your posts for tips on making a hull more pleasing to the eye, as - based on photos - you are a quality builder.

    Lol, it's hard to compliment someone without sounding like a suck-up. I have already purchased the plans/patterns, long ago, but plan to make some alterations. Unfortunately, the designer has retired, so I'll be having to have another designer/N.A. check & approve my changes. One major structural change will be "floating"(stand-off) frames. My question concerning overlap was based on an earlier post of yours, wherein - if I understood you correctly - you were initially using small tacks for joining your longs to your frames, then, plating/welding up your shell plate, longs to plate, etc., then coming back & fairing any flat areas of your shell plate - relieving the shell plate by breaking long to frame tacks, where necessary, & dog-and-wedging the plate - then welding the longs-to-frame joints. Have I described your sequence correctly? In breaking loose the long-to-frame joints, do you not find that the shell plate tends to spring outboard? If so, am I correct in my understanding that you then ensure that the shell plate only expands outward enough to still allow an overlap of at least 60% of the width of the longitudinal? Conversely, did my understanding of what you have said go sideways at some point?

    Others feel free to confirm whether I have correctly understood this aspect of the discussion, or missed something. Though these forums often disintegrate into a clash of the titans, my interest in building the most aesthetically pleasing boats - taking into consideration that these will be multi-chine & in steel - far outweighs any bruising my ego may take in being "spoken down to". I do not consider any one designer or builder on these forums to have all of the answers, and, in the end, I'll take what is of value & build in my own way, instituting practices I have learned here, and in a few decades of steelwork. As all contributors to these forums have taken time to assist others in boat design & construction, most without thought of compensation for their time & efforts, I say thanks.
    Mike
    As time permits, I'll upload some photos to my gallery that depict a few of the vessels I work/have worked on, including my boss's personal toy, Attessa lV, an aluminum yacht that has recently been stretched to satisfy his recurring "2-footitis".
     
  6. Wynand N
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    Wynand N Retired Steelboatbuilder

    Lets me put it more simply how I go about it.

    1. Install all longitudinal into frame slots and just temporary tack weld to frames.
    2. Install plating and let the steel takes its natural "curve" and do not force to stringers that can result in hollows, bumps etc. At this stage just tack weld plates together and where it touches the longs.
    3. After plating check that plating is fair and if not so, make necessary adjustments.
    4. Now get under the hull (if built upside down) and adjust the longs - where the longs are away from the plating, push the stringers to the plating and tack weld.
    5. You will find that with the plating taking its natural curvature, some stringers needs to be loosen from the frames and pushed out to the plate - do that.
    6. When all the plating is fair and to your acceptance, and all the stringers against the plating, its is time to "lock" the stringers to the frames by welding them solid to frames.
    6. With all stringers weld fast to the frames, space weld all the stringers to the hull plating as per designer spec.
    7. When completed, start welding the hull on the inside until finished.
    8. Back grind all the welds from the OUTSIDE of hull until into solid material without slag holes etc and weld hull from the outside.

    Some of the stringers that needs to be pushed away from the frames are few and far between and usually only by a few mm.

    I hope this clear it up Mike.
     
  7. welder/fitter
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    welder/fitter Senior Member

    Yes, very clear.
    Thank you, Wynand.
     
  8. Brent Swain
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    Brent Swain Member

    When, during the Falklands war, I heard a CBC reporter interviewing an Argentinian, the reporter commented "It didn't make much common sense for Argentina to invade at this time." The Argentinian said "My friend , as I'm sure you will understand, what you call common sense is the least common of all the senses"
    True in yacht design as well. Amen
    Brent
     
  9. tazmann
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    tazmann Senior Member

    Welder/fitter
    Question, Would converting existing mutichine frames to standoff style be a major undertaking?
    I have a couple multichine plans from years back myself. One of them is a 31' cutter rigged. For some reason i have allways liked the layout on that one.
    Tom
     
  10. welder/fitter
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    welder/fitter Senior Member

    Lol, Gee, Tom, I wouldn't even attempt to answer that one! With all of the designers, here, and Wynand; who's done this before...

    Personally, I'd take the plans to a designer & have them make the necessary determinations. In this forum, Dudley Dix & Wynand mentioned that Wynand had done this with one, or more, of Dudley's designs, in consultation with Dudley. Though it may seem a simple enough alteration, better to make use of the sound advice of an experienced designer, than to gamble on creating high stress points, imbalance, etc., don't you think? The way I see it, a paid consultation is a small investment, when one considers the costs of building a boat. I plan to go with "floating"(stand-off) frames & make significant changes to the transom, when building my version of the Lodestar(Hankinson/Glen-L). I wouldn't think of doing so without a qualified N.A.'s/designer's input.

    BTW, how is your origamiboat coming along?

    Mike
     
  11. Ad Hoc
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    Ad Hoc Naval Architect

    It really depends on the loads involved and also whether you want the vessel classed and surveyed. Not to mention the parameters of the vessel and alloys being used. Anything is possible, but the changes required to satisfy many "parties" may not be the desired end result first envisaged!
     
  12. tazmann
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    tazmann Senior Member

    I must have missed the topic on converting. I dont think I would atemped doing it myself with my farm code enineering skills LOL.
    Just chating here, Doing a round bilge I can see a major benafit from the floating frames but on a multi chine built frame first with strieght panel sections chine to chine except for the forward lower section at the bow, I cant see much benafit to change it? Just trying to picture it in my mind.
    I have the study plans to the Lodstar, cool boat but a lot of boat.
    I bought the plans for the Aurora and the Union Jack from Glen-L many years ago.
    The 26 I need to get back to painting the finish coats but been busy with other projects and waiting for better weather,spring hopfully.
    Tom
     
  13. Dudley Dix
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    Dudley Dix Designer

    You really should get the advice of the designer of the boat. The designer may not want you to make the change.

    I try to stick to a policy of not advising on designs drawn by others. I have principles in mind when I draw a boat and don't like it when others interfere in my designs without properly considering the reasons behind my decisions. The original designer is always the best source of advice because only he knows the full story and history behind his decisions as well as how much can be changed without inviting potential problems.
     
  14. welder/fitter
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    welder/fitter Senior Member

    Tom,
    Wynand's explanation is on page one of this thread, complete with photos. Dudley Dix's associated post is on page two. As you can appreciate, even without heavy frame-shell plate welds, laying the plate directly across the frames can lead to that checkerboard/hungry horse look, over time. In the shipyards, this is an advantage for the fitter - as I previously mentioned - when doing repairs from outside the shell, cutting in. When we pass our soapstone over the shell, an outline of the frame is apparent to the trained eye. over the years, the outline of the outboard edge of the frame becomes visible to all. As the work is being performed on commercial vessels, we don't worry about it, unless appearances are paramount.

    Same idea that you are going with on the origamis, with the exception that the transverse frames are kept. With the size of the Lodestar, I prefer to have transverse frames and, of course, Hankinson designed the Lodestar to have them.

    There are a number of pictures posted on the Glen-L site of a Lodestar being constructed. You're right, big boat. Fortunately, I will be employing others in the build. Because I'm shooting for making the boat look as good as possible, I will be hiring experienced joiners to finish the interior.

    After viewing a Lodestar - built to specs - that was being sold on Ebay, my feelings regarding the aesthetics of the transom were confirmed, not very pretty, so it has to be changed. I believe that the fellow building the one shown on Glen-L is planning to make changes to his transom, as well.

    Mike

    P.S. Sorry to hear that Evan Shaler has fallen out of favour with some of the origami crowd. He's built some really nice looking boats, same level of quality as the one you've built.
     

  15. tazmann
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    tazmann Senior Member

    Ok Thanks Mike
    The over time part I was not thinking about, That does make sense to offset the frames a bit if possable.
    I need to go look at the construction photos of the loadstar, havnt been on there site for quite a while. I like the layout on the loadstar but for me it would be a bit to much time and $ to even consider.
    Dont know what happend between Even and Brent there,cant comment one way or the other.
    Tom
     
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