Corner Chine Extrusion Aluminum??

Discussion in 'Metal Boat Building' started by G Anderson, Jan 18, 2015.

  1. G Anderson
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    G Anderson New Member

    Hello
    I am going to build a 20' plane jane aluminum flat bottom boat and want to use 1/8" for the bottom and use .100" for the sides. I would like to use a pre made extruded corner chine but I am having a hard time to find a supplier.
    I understand there are several in the NW but some of these extrusions are proprietary to a certain boat builder but I am thinking there must be some off the shelf available as well.
    I"d be appreciative of any other ideas on joining the side to the bottom.
     
  2. Ad Hoc
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    Ad Hoc Naval Architect

    I would not use an extrusion, if it is part of the hull structure. By that I mean say an angle bar " L " where the vertical left hand end of the L is attached to the side plate and the lower right hand end is attached to the bottom plate.

    All Class societies no longer allow 6000 series below the water line owing to its higher copper content and is more prone to corrosion.

    However a simple solution I've used many times where materials are scare or the fabricators want a 'simpler' joint, try this:

    Typical Chine with FB detail.jpg
     
  3. Mr Efficiency
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    Mr Efficiency Senior Member

    The small (trailable) alloy boat market is awash with boats fabricated with extrusions at the chine, keel, sheer etc. Are they necessarily using this suspect 6000 series material ?
     
  4. Ad Hoc
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    Ad Hoc Naval Architect

    The clue is in bold underlined :D
     
  5. Mr Efficiency
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    Mr Efficiency Senior Member

    This 20 foot punt is a small, trailable, alloy boat, what is the "clue" I'm missing ?
     
  6. Ad Hoc
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    Ad Hoc Naval Architect

    1) It is small, ergo NOT built to Class rules
    and
    2) Being trail-able, also means it is not constantly immersed in sea water...possibly even, if a good owner, washed down after use.
     
  7. Mr Efficiency
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    Mr Efficiency Senior Member

    Presumably he is not going to have his boat moored, so the extrusion should be OK ?
     
  8. Mr Efficiency
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    Mr Efficiency Senior Member

    There was actually a small trailer boat in alloy on the market at one stage where all the panels were joined by extrusions, and no welding. Not sure how it all sealed or didn't come apart, but I saw one on the water the other day, so must have been somewhat successful.
     
  9. waikikin
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    waikikin Senior Member

    I remember that, but not the brand, mid-late eighties maybe, a small boatshed I worked/locumed at had an alloy hire fleet, the proprietor used a lot of sika tooling grade adhesive sealant on the moored vessels, prolly fine on a trailer & the suspect boats well used/ paid for & depreciated once he was applying the gooey.
    Jeff
     
  10. Mr Efficiency
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    Mr Efficiency Senior Member

    Yes, I think it had a slightly grandiose brand name considering it was a fairly humble little boat, but the name of it evades me for the moment.
     
  11. Kevin Morin
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    Kevin Morin Junior Member

    Small boats' welded chine

    G A', just weld them together don't bother with an extrusion.

    Most manufactured boats have weld uniformity problems due to the high cost of decently skilled welders, so they use an inside only (weld) chine extrusion so there is no weld outside the extrusion-to-topsides seam!!! (why are they called welded boats? )

    This (no weld seam) sells better than poor quality weld seams so.... these extrusions provide a 'looks only' solution- its very widely used. These chine extrusions are 98% proprietary, that is- the company using these extrusions owns the 'extrusion plate' in the US. Or at least owns the pattern rights to the plate they paid to have cut and then they agree to buy 2-3 ton lots of that extrusion at one time.

    The cost is not prohibitive, even small builders who will be making a couple of dozen boats can afford this process, and that allows a builder to enjoy profit from their innovation and investment. But the public generally can't buy these products without going to the expense mentioned here.

    So looking for the chine or sheer extrusions that you see on manufactured boats could be futile? I've been building in the NW (Alaska) since the 1970's and have not seen chine extrusion readily available at any time.

    But there is no reason that if you can weld a boat that has 0.100" sides and 0.125" bottom that you can't weld the two pieces together. If this super light weight boat will be in rocks and you're concerned the chine will suffer impact regularly; simply use 6061-T6 alloy 1-1/2" x 1-1/2" angle extrusion to cover the chine and stitch the "chine cover" with short staggered stitches so you can remove it in the future and replace it when the extrusion gets banged up and is to damaged to remain on the pram/jon boat/skiff.


    cheers,
    Kevin Morin
    Kenai, AK
     
  12. G Anderson
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    G Anderson New Member

    Thanks for the reply guys.
    Kevin that sounds about right as far as the extrusions go and the reasons. I have attached the boat I currently own which is a 16' and I basically want to build the same boat in a 20', to run on some remote steelhead streams.
    I am never too sure about the bottom in my current boat as it is pretty "flexy" but maybe that is why it works. It is light enough to bounce up and off most rocks, but obviously the goal is not to hit any. I am assuming it is made out of 5052, as it would have been the least expensive.

    If I wasn't too worried about cosmetics on the new one, could I just put the side (.100) on top of the bottom and inset it about 1/4'' and run a bead on the inside and outside. I am thinking that should be a trouble free connection?
    I'd also be interested in anyone's thoughts on material. I was thinking about using 5058. A friend of mine is using 6061 for bottom material and has built 4 boats like that and swears by it. Being harder the 6061 slides off rocks instead of sticking to them is the thinking. Another line of thinking is that a 5052 would bend instead of tearing in this application.

    This boat will never stay in the water very long and will be always in fresh.

    Thanks in advance.
     

    Attached Files:

  13. Kevin Morin
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    Kevin Morin Junior Member

    flat bottom skiff materials

    G Anderson,

    I'd avoid 6061 since it will crack on impact way before 5052 or 5086 or 5083 all of which are much more malleable and better for rock impact in my experience.

    I don't care for the T chine shape preferring to use an inside edge-to-edge fit, this gives a better shape control during tackup, where the outer edge of the bottom panel is exact, but even with a offset gauge I've seen some "wavy" chines resulting in sides of the same shape.

    The T joint isn't stronger in actual use, unless you're willing to leave some several thicknesses of material outside the weld area? I'd prefer a edge to edge fit, then the outside weld is a fully penetrating fillet with a naturally formed V the thickness of the material. The inside weld is back chipped and then an even fillet leaving a slight thickening of the two plates/sheets but still as strong in practice as the T, if there's a real risk of rupture or even serious deflection cover the chine like I said above.

    If the skiff is to be 20' LOA I'd go with 0.160" bottom and 1.25 sides so I could reduce the framing needed in the expanses of a skiff of that size. Otherwise you'll have to frame and frame and frame, and as you've noticed already your current skiff bottom flexes...! a 20' skiff with 0.100" sides is going to be subject to some easy torsional flexure (corner to corner twisting) without some fairly extensive framing elements?

    The difference in all up weight isn't enough with the slightly heavier scantlings in the hull to make much difference. I don't think this long wide skiff will draw another 1/2".

    best alloy you can use is 5083 or 5086; the former is much harder to find than the latter (in the Puget Sound area(s) ) so use '86 for the best rock performance for the cost if you're in steel head areas.

    or ? if you're energetic then put some UHMW on the bottom and use that to slide off rocks.

    Cheers,
    Kevin Morin
    Kenai, AK
     
  14. yofish

    yofish Previous Member

    View attachment 97379

    Simple? If you don't mind, could you call out the welding schedule for this assembly?
     

  15. Ad Hoc
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    Ad Hoc Naval Architect

    Well, i thought it would be obvious, since it is a watertight boundary.

    The fillet weld is to be consistent with the thinnest material you are welding and continuous on both sides of the FB as it is a watertight boundary..that's all. Simple!
     
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