Reversible connection of structural fiberglass components

Discussion in 'Boat Design' started by Johannes2021, Jan 16, 2023.

  1. Johannes2021
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    Johannes2021 Junior Member

    Hi,

    In order to meet the requirement of max modular dimensions for luggage check-in, I actually consider how to best connect purpose-built kayaks in a cat configuration. I.e. this is to be flown like other sporting equipment.

    Have so far fiberglassed a scaled-down model boat as a manufacturing test article after tinkering a bit with CAD, cutting the printout out of polymer foils, bending these into an exterior cardboard skeleton, gluing, and fiberglassing into this female mold.

    Now I want to try to fiberglass a kayak 200×70×30 cm as some airlines allow total dimensions of 300 cm for sporting equipment. But how to connect the kayaks without ending up with a wiggling mess?

    Connect it with wires (nylon, polyester, steel?) and aluminum rods as spars or perhaps something entirely different. I dislike that it's not simply one structural article/hull but am compelled to actually try the modular approach for portability, to meet check-in requirements.
     
    Last edited: Jan 18, 2023
  2. Johannes2021
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    Johannes2021 Junior Member

    Have edited the above as it was a bit flawed. Am assuming springs should be used to keep mentioned wires under tension. Perhaps marine-rated springs with respect to corrosion and whether there are better approaches
     
  3. fallguy
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    fallguy Senior Member

    I would consider wood beam and a Wharram type lashing.

    For some food for thought, I recommend you read Gary Dierking's great book on Outrigger canoes.

    Some wobble is okay, so you know. It is the old idea of bend, not break. This is done at the lashing, so the connection is strong, but gives under high strain.

    I have only lashed outriggers, not two boats, but the concept would be similar.

    The basic idea I would pursue is some type of socket or pylon on the yak on the center for n aft, with the lashing on each boats (inside) edge. This would effectively become like four points of contact versus just connecting at the pylon. Of course 6 points of contact are better, but then you'll be running up against your 2M limit for beam length?

    I would imagine you are already close to having a problem banging paddles on any inside steering. You could perhaps offset the pylon which would normally be centered. Or, perhaps you could make a pinned beam which would allow it to be much longer.

    My outriggers use simple tire tube lashings. When tied wrong; they are useless. When tied correctly, I'd trust them in 4' seas, although I'd not venture out in that; just enough to get to shore!
     
    Last edited: Jan 17, 2023
  4. fallguy
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    fallguy Senior Member

    One of the challenges for you will be making the pylon or socket strong enough. It cannot be mounted on a 4mm okume deck or like light glass deck, so you'll need to consider where the boat is strong enough to not break; possibly this lends itself to a pinned beam and lashing not on a pylon, but on each side of the deck at the hull to deck join.

    Hopefully you get a few more people chiming in. Maybe even an expert on this sort of thing @garydierking .
     
  5. Johannes2021
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    Johannes2021 Junior Member

    Thank you. That book looks like just about what to read to not make these decisions in a vacuum. Fascinating, the history of these outriggers.
    Wood seems nice in terms of manufacturing but I am worried that it will add a lot of weight to the check-in luggage.
    I was considering if to have two beams/rods such that fiberglass panels can be put on the two.
     
  6. Johannes2021
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    Johannes2021 Junior Member

    Yes, that is holding me back right now from starting the CAD design. How/where to mount it such that it will not break, have longevity, is easy to manufacture and maintain
     
  7. Rumars
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    Rumars Senior Member

    Do you have some particular aversion to nuts and bolts?
    If you have a mast it can be done with sockets and the rigging holds everything together.
    Post a picture of your model so we can see what's going on.
     
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  8. fallguy
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    fallguy Senior Member

    As Rumars said, to help you more specifically would require more details. For example, are the boats side by side or gapped underway.

    What is nice about wood is it can be laminated and if you need an odd shape; the lamination can accomodate. Aluminum, on the other hand is typically used when the mating surfaces are made more planar themselves. And then for a narrow setup, bolting can be done.

    But if you want to be wider for stability in rougher seas, then a longer beam and lashings would be the way I'd go.

    All depends on the details, as always..
     
  9. Johannes2021
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    Johannes2021 Junior Member

    No mast planned yet for this iteration. Albeit for a later one perhaps. Interesting though. You mean like using a common mounting for mast and transverse beam?
    The required fiberglass thickness at the mounting: I hesitate to decide on that absent experience or an estimate for the stresses. Another issue is space given that most components should fit into these 200×70×30cm packages.
    A pic of the design and fiberglassed outcome of the manufacturing test model is below.
    It doesn't fit the design of the prospective cat canoes on which I settled after doing this fiberglassing exercise, being so far only a test run.
    upload_2023-1-18_15-19-15.png
     
  10. Johannes2021
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    Johannes2021 Junior Member

    It would be kept wide for stability, i.e. gapped. Perhaps the mounting will turn out as constrained by other factors. Hmm, will ponder over it a while whilst reading up on the outriggers...
     
  11. Rumars
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    Rumars Senior Member

    It helps if you take a look around instead of trying to reinvent the wheel. On this size cat the beam is usually bolted on by means of an elevated pilon, but it can be also done big boat style by having a recess in the hull. Simplest way is to make the corresponding bulkhead higher and simply bolt the beam to it. Where a bolt goes you have local reinforcements.
    Look here, there's a picture with a very suitable system. Wooden beach cat https://www.boatdesign.net/threads/wooden-beach-cat.8789/

    Since a 2m boat is not really good, spend some time thinking how you can make it longer. Here are some examples, make it so that the pieces nest like the Pakayak or Backyak.
    https://www.reddit.com/r/Kayaking/comments/rd9e1m/modular_kayak_sectional_kayak_3part_kayak_split/
     
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  12. fallguy
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    fallguy Senior Member

    Rumars point about the hull length should not be glossed over.

    I have a short fat canoe with a l/b of about 5. It is a decent boat, but a tough paddle; more so in a headwind, and in 15 knot winds its near impossible without both guys goin hard.
     

  13. Johannes2021
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    Johannes2021 Junior Member

    These modular solutions are amazing. I had thought about later using four of the planned "kayaks" such that two face backward, having longitudinally two stump sterns attached to each other, making it 4 m long. And addressing the problem of the boat being too shallow by having packaged inside a sort of thick bodyboard that would during cat-assembly be attached below the bottom, resulting in a bulbous bow. Foam that low might mean though a high center of gravity, albeit perhaps not prohibitive for a cat. But the bulkhead compartmentalized solution seems to perform better.

    Have considered the bulkhead compartmentalization but was earlier concerned that I couldn't manufacture the outer skin of the modules even enough. But now that I see that this has already amply been done, it seems one can just manufacture the entire boat with double-walled bulkheads and saw it in pieces in between. IIRC I saw that this was already described in one thread here but I failed to notice then that this also ascertains evenness.

    E.g. four nested modules in a 100 cm cube for a ~4 m boat: The innermost bow module of a nested package could be filled with floatation foam. So for the stern, I might want floatation bags.

    Connecting the four modules: Will have to do that in CAD to be intelligible. Will circulate it below
     
    Last edited: Jan 21, 2023
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