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Newbie with questions on foldable paddleboard via Skin-on-frame with recycled stuff

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  • Newbie with questions on foldable paddleboard via Skin-on-frame with recycled stuff

    Hi, I'm terry. a total Nubie here with my first post.

    I'm looking to use recycled material to build a foldable paddleboard that will fit in my car. I've multiple designs for the folding joint i want to test, but here I am mostly asking about the actual paddleboard structure. I want to keep weight down and after various considerations and discussions over at I've narrowed my design to skin-on-frame. People over at swaylocks have already been telling me to just buy new stuff and use epoxy etc.. but I'm committed to doing it with as much recycled materials as I can.

    I've been reading many many useful posts here and looking at nice full size designs, e.g.
    Dave Gentry's designs, and others. But I've not seen any plans for 2-piece folding SOF paddleboards so I'm doing my own design. My design has 2 parts about 68" long, 32" wide, 5" thick. I'll be using mostly recycled plywood (exterior grade) for stingers/ribs and for the plywood deck and already have enough from various crates at work. I also have some 1x4" frames from some of the crates though its not very good quality, while the ply is pretty good ACX.

    Here is the rough design idea first sketch and then an initial CAD with some internal layouts though its incomplete, but it provides background for the questions.

    1) The framing/ribs is all from only 1/4" but many of the SOF kayaks and canoes I've seen here are all using 1/2 or 3/4 for their frames and ribs. By calculations (and those of the sagulator) suggest 1/4 will be okay at the spans of this design but my CAD program will not do stress for actual plywood so I have to approximate. In the current/CAD model I have 4 cross frames and a central stringer, 2 side supports . All of these are are full height and will have cutouts like the stringer shows. In addition there 4 long ribs top and bottom that are 1" high.. Not show in the cad but the region where I stand will have 1/4" ply decking added over the skin. Since part of the strength of SOF comes from compression of the frame, and my skinning won't shrink, 'll also be adding rib-rapping, internal cross connections and diagonal connections using recycled PET-plastic striping that I can heat-shrink to get good tight compression, though I've not designed the wrapping pattern yet. I've not actually seen this in any post/designs here but it seems to make sense to me but want to ask for feedback from this community.

    2) I have dozens of yards of pre-shrunk polyester cloth with my old my academic posters printed on them. Most of the posters are 36"x96". So I cannot do a full wrap of the hull with 1 seam, but could wrap top or deck and wrap up part of the 5" thickness. And because this is all pre-shrunk, I have to pull it tight. This leads to multiple questions:
    2a). How does shape impact the ability to pull it tight without wrinkles? My above design is going for both taper on the sides and a rocker, so curved in two dimensions. I am just asking for trouble with getting that wrinkle free? I have also considered a more kayak like displacement shape without a rocker and more of point instead of rounded front. Would that be easier to skin?
    2b) How tight a corner can I turn with the skin along the long edge? are 90 degree corners okay assuming support behind them? 120 degrees? Do corners increase difficulty with wrinkles?
    2c) Paddleboard/Surfboard normally have a thinner rounded rail. I did not want just the 5" thick board all the way to the edge so was going to have a 2" outer rail and about 2" for that to angle to the 5" core of the board. the 2" and 5" would have a full supported edge but nothing in between, so I expect a largely linear cloth, but with the curve of the board to a point is that going to be impossible to get wrinkle free?
    2d) An alternative is to go with fully supported but angled sides at say 120degree inside angle the bottom and larger top. This would have fully supported wood region for displacement, a reasonable angle "rail region" but should still be stable. With this I could staple/glue along the full supported side to smooth out any wrinkles. I've seen this idea of glue for fabric-on-foam designs but never a skin-on-frame design. This had the advantage of not needing stitching but Is gluing large sections a problem? Any suggestions on keeping it tight while the glue dries? I'l probably add a wooden rub-rib on the outside either way to protect from the paddle, so I can use that to cover any seam.

    I think that is enough for now.

    Last edited by dr_innovation; 08-19-2021, 09:06 AM. Reason: fix some typos and correct material size