Aluminum boat framing

Discussion in 'Metal Boat Building' started by welder/fitter, Sep 14, 2008.

  1. welder/fitter
    Joined: Jun 2008
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    welder/fitter Senior Member

    I was chatting with someone whom is planning to build an aluminum sailboat - I think he said 42 feet - and was interested in his plan for fabricating his frames. He plans to cut(plasma) each frame from a single sheet, rather than "piecing" it together, thus avoiding weakened joints. As I have no experience in building aluminum boats, I'm interested in the thoughts of those who do.
     
  2. waikikin
    Joined: Jan 2006
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    waikikin Senior Member

    Sounds like an exxy option, cutting segments such as frames/ floors / deck beams with a rider bar set around the interior perimeter is more typical & heaps cheaper esp as the frames get bigger, you might cut from a single plate up fwd & collision blkhead & lazarette etc & see a saving in effort, LazyJ might chime in with an opinion as he's into the alu, my building in metal experience in mainly in steel with some repar/fitout to alu. All the best from Jeff.
     
  3. lazeyjack

    lazeyjack Guest

    yes thats common practice now, you can flange it up if you want
    the tensile is not as great in 5083, but you can up the scantlings, , limits on size of plate is about 2m wide, , generally you get abt 20% waste on metal, per tonne, which you sell back to scrap,, of course to nest is the key,
     
  4. kmorin
    Joined: Apr 2005
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    kmorin Senior Member

    NC cutting and nested parts in aluminum

    welder/fitter,

    most boat budgets need to keep the waste % down because of the high cost of aluminum- and nesting NC parts so that frames are built from several parts is the most efficient means of using the plate purchased.

    Joints- or butts- in frames are not weak spots if the designer knows they're there. Usually ring frames have an added flange roughly parallel to the keel plane - and this combined with correct welded joints makes the subpart-assembled frame, normal and very (materials) cost effective.

    The theory of failed framing butt joints - needed to make your friend's concerns valid and justifying his increased cost of frames- is not accurate.

    Now, if he just doesn't want to take the extra time to butt weld the parts; well, that's a time vs value choice but there is no strength issue involved. Its easy to say our time is worth more than the extra metal needed and just cut the frame's from as large a plate as can be found. I've purchased 8' wide stock in the Puget Sound, so this might mean many fewer (short) welds, but surely much more plate.

    Cheers,
    kmorin
     
  5. CTMD
    Joined: Dec 2007
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    CTMD Naval Architect

    I've traditionally subdivided cut frames but an increasing number of builders have been asking for frames to be kept as single parts where possible. It seems that when you do a cost analysis the time spend setting out and welding frames costs more than the extra wasted material.
     
  6. kmorin
    Joined: Apr 2005
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    kmorin Senior Member

    Home Builder vs Yard Costs

    CTMD,

    To me, it appeared the question was raised about someone who would be building their own boat. Owner/builders and yard costs are fairly separate universes of cost. Paying a yard to do many jobs to the finest levels of finish moves a yacht from affordable into more than most of use make in a lifetime. So if it were yard labor that was being conserved- it may buy that metal, if it is an owner's time in a 10k/ hr project; maybe not.

    This site and others are full of examples of owner builders doing better by far, in terms or finished work versus costs, than they'd care to pay a yard to do for them. So, if the owner has just sold his Microsoft shares that he's held for the last 15 years, well, call the NC profiler and have those one piece frames out as single piece material. On the other hand, if he's building his 40'er by hand a few more joints won't make any difference in the next few years of his build and he'd save plenty and get some warm up welding in to boot.

    The main point is there is no strength issues with the hull on one side and the flange on the other- what's to fail, so a strength issue is not justification- labor costs? OK if he's hiring the work done- but that's altogether another kettle...

    Cheers,
     
  7. lazeyjack

    lazeyjack Guest

    as always the key when framing in parts, beam, sides, floors, gussets, is accurate fit up, with correct joint design, overlapping the side by 2.5 w, onto floors is lloyds rules, , I have never built a boat from cut frames, so far, but our latest is, , if you look at my gallery you will see the use of t,s, so 3 parts, sides, beam , and floor, unless it is chines
    the key is this, draw the section full size, ,cut of press the parts the parts, ands use pigs of lead to hold all down, , run fast hot tack, in middle of each joint, first and watch the frame on the loft, if you are really going to be into this, I can draw a weld sequence
     
  8. lazeyjack

    lazeyjack Guest

    I was writing a book, flagged it away, but this is the method I use to shape sections,
    draw the plan, and folllow this,, it'll work on all sections,, , there is a point at which, say if youa re pressing flats, the width must not be too great compared with thickness, trial error will show, or it'll crumple
    Ahorizontal press is really a must in boatbuilding, bit like a pipebender, I used to make mine from old pumps and rams from dozers etc, , valves same, the bigger the table top the better allthough 3 feet x 18 inches will do, , pegs from 9 inches apart to 24 inches
     

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  9. lazeyjack

    lazeyjack Guest

    bigger pic
     

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  10. welder/fitter
    Joined: Jun 2008
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    welder/fitter Senior Member

    Interesting perspectives. I don't actually know the guy, someone I met at a marina pub. I had Colvin's book with me, as I was lending it to a friend & this guy says, "Why would you build a steel boat?" LMAO, I thought Lazeyjack had flown north for the winter! As you can imagine, the discussion carried on as if it were in an online boatbuilding group. When I asked him if he had concerns over joint strength, he told me of his plan for the frames. I would assume that he meant to cut half frames & join them, as I can't see where he'd get big enough plates for full frame cut-outs. Subsequently, I began to wonder if this was standard practice when building the Al boats.

    The owner of the shipyard I work at has a pretty big yacht, "Attessa IV", which is currently being stretched. Though I'm not working on it - off with a bent wing - I'm going to hop aboard next week & have a good look at what's keeping her together. Actually, The owner also has 3 aluminum catamaran ferries - if anyone's looking for a superyacht with jet drives - which cost our provincial gov. about $450mil each. My boss bought them for $19mil, total(god love the politicians).
    Mike
     
  11. lazeyjack

    lazeyjack Guest

    i did go to Holland, did what I wanted to do, and now want to know where to build
    I drove 4000kn in 6 days
    here are some pics i was at boat show on water in Ijmuiden and in Austria I saw this old dock thingie
    it may seem odd that i spent such a lot money to research this, but was essential to see what was selling up there, and standards i fully intended stay up there but the melting of markets necessitated a speedy return
    FITWELD I would like to phone you abt powerpacs
     

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  12. Rusty Bucket
    Joined: Feb 2007
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    Location: florida

    Rusty Bucket Junior Member

    Hey everybody, Maybe I missed something but I wonder how the builder is going to create a "flange" for his cut frames. Dosen't the design criteria require some sort of 90 degree stiffening to prevent deflection under load? The frames don't have to be butt welded, I lapped the the angle at the chine on the 25' al. boat I just finished. Wow, I just remembered, the Roberts 36 I built back in 1978 didn't have any flanges just 3/8 by 3 flat bar. Until recently the Roberts was the smallest metal boat I had built so maybe I'm used to heavier construction methods. Regards, rusty
     
  13. lazeyjack

    lazeyjack Guest

    flange
    no , you can do without, BUT you must up the thickness of your flat bars, if I were doing a 35, I would have no stringers and frames on 400mm centres, of 60x10 flat, if I was using flat bar, or 50x40x6 in t,s
    if you have shape, t,s are better than angles, cos they dont warp as much when you shape, they do warp a little and the skill is in keeping twist out of .Angles twist like mad, so you can get crafty and tack two angle pairs back to back then press both halves together, when you have the shape, spilt and they will then need some adjustment to get em exact
     

  14. welder/fitter
    Joined: Jun 2008
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    welder/fitter Senior Member

    Lazeyjack, I pm'd you.
     
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