Advice, Stitch and Glue construction - novice

Discussion in 'Boatbuilding' started by cpodest, Jun 24, 2014.

  1. cpodest
    Joined: Mar 2014
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    Location: Ilhabela - Brasil

    cpodest The Beginner

    Dear Guys,

    I'm building a simple flattie. I have no experience building boats and also i have no experience with the stitch and glue technique. So, I really appreciate your help on this issue.
    The design is 3.4mts length and 1.3 mts beam, so, bottom and sides need to be made of two parts using buttblokcs joints. I'm using plywood 2.2 x 1.8 mts

    In the picture attached there are two options, could you help me to decide which one to use it?
    -the first one could be result in a big "weak" point. But the buttblocks, will be hide under a seat.
    - the second option (B), would result in a strong boat , but would bring me a lot of work in order to hide the buttblocks.

    Can I use an intermediary solution. I mean, separate the cut of the sides and the bottom 15.. 20 or 30 cm?

    (please, do not recomend me to use scarf joints... I don't have resources to make it)
    Sorry for my english, and every doubt or sugestion will be welcomed ¡
    Thanks a lot for your help
     

    Attached Files:

  2. TANSL
    Joined: Sep 2011
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    TANSL Senior Member

    Without having analyzed sketches in depth, the first thing I can think to say is that you should avoid joints in bottom and sides coincide in the same cross section.
     
  3. lewisboats
    Joined: Oct 2002
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    lewisboats Obsessed Member

    Offsetting the butt blocks is actually a good idea, so you are fine there.
     
  4. rwatson
    Joined: Aug 2007
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    Location: Tasmania,Australia

    rwatson Senior Member

    Butt blocks are stronger than the wood they join if you are using epoxy or decent glue, so you don't have to worry about lining them up, especially on a little boat like this.

    "On our test models we use standard 4'x8' sheets, joined using one of the methods detailed below. Both methods have proven to be as strong, or stronger, than the plywood being joined."
    https://www.glen-l.com/wood-plywood/scarf-butt.html


    Do whatever looks good.

    I hope that those sketches are not to scale, as the will resulting in a funny looking boat with a hogged keel line.
     
    Last edited: Jun 30, 2014
  5. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    Use the Payson butt joint or a scarf, instead of butt blocks (which just suck). This way you don't have to hide anything, as the result is flush, which under paint is seamless. If finished bright, you'll want a scarf, done neatly, but they're still seamless.

    The side panel layouts look correct, given the resolution. The boat has modest rocker, in fact I think not enough, though I don't know the SOR.
     
  6. TANSL
    Joined: Sep 2011
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    TANSL Senior Member

    Indeed, rwatson, the method of attachment is decisive in establishing the strength of the joint. In building metal boats is completely normal to have a complete ring binding the various blocks that form the hull and deck. However, I do not think it's very expensive, but very convenient, offset the butts.
    Why not do it right?, especially if it does not cost a penny more.
     
  7. SukiSolo
    Joined: Dec 2012
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    SukiSolo Senior Member

    Mostly I find people have an irrational fear of scarf joints. They are not particularly difficult, if you have a sharp plane. The only thing difficult is clamping wide ones, but this can be overcome with lightly cambered 3 X 2 clamped up and wedged. So do not be frightened of doing a scarf joint, just because you have not done one before. Any ratio over 7:1 is OK.

    Remember to dry fit it and trial clamp it prior to actually putting the glue on the joint and clamping for real. It will tend to slide more with the glue so just use a bit of masking tape to help hold position during clamping. Masking the areas you do not want covered in glue can also be useful depending on end finish.

    So your 'resources' for a scarf joint are a No 4 plane and about 4 clamps plus a couple of 3 x 2 battens and a few wedges, oh, and proper waterproof glue. Not a lot considering you will need pretty much all those to make the rest of the boat anyway!.

    The main advantage of the Payson butt joint type, is you do not lose sheet length, as far as I can see.
     
  8. rwatson
    Joined: Aug 2007
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    rwatson Senior Member

    I cant see it myself - assuming the sides are straight up and down ( given the plumb stem ), with a little bit of rocker - the actual sides when unrolled dont seem to match the original plans.

    If I increased the amount of rocker, the curves on either end would curve upwards, not down
     

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  9. lewisboats
    Joined: Oct 2002
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    lewisboats Obsessed Member

    I'd say there is a fair amount of flair to the sides, warping to a near plumb stem. I get those same results.

    ETA:

    I just knocked this out to illustrate:

    [​IMG]

    [​IMG]

    [​IMG]

    This has a bit more rake to the transom but otherwise very close...

    [​IMG]
     
  10. cpodest
    Joined: Mar 2014
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    Location: Ilhabela - Brasil

    cpodest The Beginner

    Dear Guys,

    Thanks so much for your help.

    In fact, the boat is very similar to the lewis´ pics.

    Sadly I messed up one of the sides panel. I could buy a new plywood plate and make the side panel again, or, I can cut only the "messed part" of the side panel and replace it for a new one......
    the questions are.... can I do that? i mean, can I have two joints (separated by 30 or 40 cm)... in the same side panel? is that safe?

    Sorry for my english, and please, any suggestion are welcomed
    Thanks a lot for your help
    Carlos
     
  11. Westfield 11
    Joined: Apr 2008
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    Westfield 11 Senior Member

    For a boat like this, any mistake can be safely fixed with epoxy and wood flour. Easy scarfs can be made with a sander and clamped with screws into a wood floor use plastic to prevent sticking. As long as you use enough sawdust and epoxy it will float just fine and will last long enough for your uses. It's your first boat and first epoxy project: don't over think things and don't worry. As long as you fill all the gaps with epoxy and wood dust it will be just fine. Beautiful is for your second boat...... Just my opinion, have fun, that's the most important part.
     
  12. cpodest
    Joined: Mar 2014
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    Location: Ilhabela - Brasil

    cpodest The Beginner

    Dear West.

    Thanks a lot for your help and you are right..is my first boat

    I´ve read and think a lot about this project..... and then, after joint the sides panels (6mm ply) I realized that I placed one of the butt joints outside of the panel... and not inside!!!!!

    Do you think that i can just cut 30 or 40 cm and replace it? the messed up side will have two joints... is there any problem with that?

    Thanks a lot
    Carlos
     
  13. Westfield 11
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    Westfield 11 Senior Member

    Structurally I would think that two butt joints with internal blocks would not be an issue. As an alternative, can you put the butt block on the correct side of the panel and then saw/chisel/knock off the one on the wrong side? If you damage the plywood, just fill with epoxy and sawdust/wood flour putty then sand smooth. If you are really worried, put a strip of fiberglass over the outside butt joint. Just cover the whole boat, inside and outside, with epoxy resin when you are done, that will seal the wood and will prevent rot in your humid climate. No uncoated wood!

    Just remember: epoxy, wood flour and fiberglass will fix anything and paint will cover everything!! You are not building a circumnavigator, if it falls apart in 5 years, so what? If you finish this one, I predict you will be planning the next one before the first year is over.
     
  14. rwatson
    Joined: Aug 2007
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    rwatson Senior Member

    30 or 40 cm is a bigger gap than I personally would fill with 'putty'.

    Mostly du to the weight factor, the epoxy expense, and the work involved.

    If I could find a small strip of wood or plywood , i would epoxy it in the centre of the gap, and level the small remaining gaps on either side with the 'putty'.

    Glassing the outside would be a good idea.

    Another benefit of putting a strip of wood might be future maintenance - because an epoxy rich layer is more prone to printhrough( sagging in the heat ) than timber.
     

  15. lewisboats
    Joined: Oct 2002
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    lewisboats Obsessed Member

    RW... I think he is talking about fairing the surface after removing the buttblock from the wrong side of the panel. This, of course, after putting another buttblock on the correct side.

    If the boat is to be painted then I don't see any problems with this method... I have done it myself when I screwed up.
     
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