a boat from foam-fiberglass laminate panels

Discussion in 'Boat Design' started by TacoFace, May 29, 2021.

  1. sharpii2
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    sharpii2 Senior Member

    11 lbs with the glass.

    About 8.5 lbs per cf without it.
     
  2. sharpii2
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    sharpii2 Senior Member

    That would certainly be a more accurate method than my estimate, but I don't think I'm that far off.

    Say I'm off by 100% on my estimate of the weight of the fiber glass sheathing, so it weighs 1.3 lbs/sf instead of the 0.65 lbs/sf I originally estimated.

    This would then be subtracted from the 2.0 lbs/sf Taco Face says this composite weighs, leaving us with 0.70 lbs/sf for a 1.875 inch thick square foot of foam.

    Now, if we devide this by 1.875 we get 0.373 lbs per board foot. Since a board foot is a square foot that is one inch thick, we can multiply this 0.373 by 12 to get what a cubic foot of this foam would weigh. This comes to 4.48 lbs/cf, which is far short of my original estimate, but far greater than a mere 2.0 lbs per cubic foot.

    But I doubt my estimate of the fiber glass weight is that far off.
    My experience with the stuff is that it has nearly neutral buoyancy.
     
  3. OneWayTraffic
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    OneWayTraffic Junior Member

    The density of glass is ~2.5 relative to water. Polyester resin ~1.2.

    It could not be neutral buoyancy. The standard CSM WR laminate is supposed to have an average RD of 1.5. Epoxy layups without mat are denser. If it's just mat then maybe a little less due to it being resin rich.
     
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  4. TacoFace
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    TacoFace Junior Member


    That sounds about right. My weights were with the skin on. 2lbs per square foot for the 2" panel. Since I'm using 2" panels. The foam itself at 8 lbs cu ft sounds reasonable.

    If 12 lbs per cubic foot is "to heavy to make boats out of", however, we should all call the US Navy immediately and warn them of the impossibility of using steel. They should use steel only for submarines.

    That kayak design sounds great. I'd probably add a few feet to it. I'd need about 300 lbs of that displacement for my self.

    ...I havent done more anything since I last posted.

    I'd love to keep all the cuts table-saw or circular saw, but if you have a design in mind I'd love to see it. Thanks for help!
     
  5. TacoFace
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    TacoFace Junior Member

    I'm guessing the nine panels would be three forward, three midship and three aft? Sharp verticle bow and stern? The fore and aft hull pieces would be triangles?

    ...I can also edge-glue these with the siding overlapping to make wider panels, but, of course, less cutting is better.

    Those compound angles for the rips are what are giving me a headache. ...but I haven't looked at those drafting programs yet.
     
  6. TacoFace
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    TacoFace Junior Member

    Yes, plywood costs much more than these panels. These are cutoffs from a factory that I can get for free.

    A stsndard plywood design could work, except that those are usually based on thin plywood that is bent into curves and then glassed over (or not). Imagine you were using 2"-thick plywood. And no kerfing and bending. No bending.


     
  7. TacoFace
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    TacoFace Junior Member

    Yes, plywood costs much more than these panels. These are cutoffs from a factory that I can get for free.

    Yes, I agree 8-some pounds without the glass is reasonable. Still doesn't matter.

    Whether it's 8 or 11 or 22 pounds per cubic foot, it is still very positively buoyant. I have no concern about this material sinking.

    If you are itching to do some math, can you calculate the edge cuts of a socker-ball pattern? Much larger of course, and with 2" wall thickness.

    What angles would you need to set your table saw to cut the wall sections of a socker-ball?

    And if the socker ball was made of 1/4 plate steel, what diameter would have neutral buoyancy?

    the last one I really don't need, but it could be fun...




     
  8. TacoFace
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    TacoFace Junior Member

    That diagram of the hull made with flat panels that approximate a curve is exactly what I'm thinking.

    And, one of my original questions was, will a faceted hull that approximates a curve function hydrodynamically approximately the same as the curved hull? Less efficient obviously, but other than that, are there any strange hydrodynamic effects?

    A standard plywood design could work, except that those are usually based on thin plywood that is bent into curves and then glassed over (or not). Imagine you were using 2"-thick plywood. And no kerfing and bending. No bending
     
  9. TacoFace
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    TacoFace Junior Member


    Yes, camper and tinyzhouse things in progress.

    Yes, this is the backwards way to build a boat. I am starting with the materials and designing from there.
     
  10. Saqa
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    Saqa Senior Member

    As long as you have factored in your desired results! I would encourage you to think along the lines of do it once and do it very very well. There has been some good suggestions on how you can use those to create a vessel with very little compromise on aesthetics and performance

    Again, encourage you to consider the suggestions of turning the panels into strip planking. This way you can build any shape you want and make it look good and perform. Lots of cutting but guess what, set your guides, and it's just repeating the cut. You would have to cut bulkheads anyway. Will be left with trimming after planking. Seriously, this sounds like less work and hassle then figuring out how to cut the facet join angles and making a well performing boat. A boat like this is not built overnight and just throw in a couple of extra days for lots of cutting and then enjoy the results

    My suggestion of layered cores would be the quickest to get a good-looking and well performing craft out of those panels too. All you need is a jigsaw to cut out each layer, stack, fill and shape. Least amount of cutting and work for a very usable end result. It's like making a giant surf board using layers. It would take me only a few hours to cut out, stack, fill and sand down a 3 - 4m kayak style hull. Another day to laminate and another two to paint to a working finish or a week to finish it to a fine detail. You can get a tender, kayak, tri, cat, SUP or similar like that

    The last one I did was an 8' x 4' tender. I laminated 4mm ply on all the flat surfaces like the top of the gunnels, foot well and such

    If I had to do a long skinny one then I would inlay some aluminium stringers in the layers. U channels can be glassed in and tapped to take a bolt. Will make easy cross-beam receptacles

    "The Flying Esky" finished! https://www.360tuna.com/threads/the-flying-esky-finished.29562/#post-321548
    This is the first time I ever tried making a boat. I had a block of styrofoam, and I was sick of fishing from the shore. It turned out really wobbly and needed outriggers, but got me on the water then. If I had that block now, I would cut it in half lengthwise and join end to end to make a longer, narrower hull and make a pair of floats from the offcutts and build a tri. Panels like yours would make it easier than my block

    A project I have in mind is to make a transmission line bass cab. I plan to take the length of 10" plastic ducting and coil it into a snail shape. Next step, saturate it with expanding foam out of a can and hand shape the still wet foam in to a snail shell shape over the coil. Let it cure, and apply thick cheap paint. Then place it in a fitting MDF box and fill it all up with foam and let it cure. Then slice it into layers, knock off the foam from outside the paint line and I will end up with templates that I can use to cut MDF plates, stack and glue to make a very strong, vibration free and heavy cab suitable for a JL Audio W7 driver and 2kw RMS of amplification with a 300B tube based line conditioning state to introduce loads of euphonic distortion between the pre and amp stages. Guess what, will take days to set up and cut but once I have my templates I can replicate anytime. I am developing this as a commercial item which I call the "Bassinga"
     
  11. sharpii2
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    sharpii2 Senior Member

    Yep. That's pretty much it.

    Because kayaks are so long and sleek, there is no need to add facet angles.

    Attached below, is my drawing. The platen on my scanner was not long enough, so the stern got chopped a bit.

    I suppose a better description of this boat would be to call it a dugout canoe, as it is quite heavy. I thought of having two bulkheads to separate the ends from the middle, but considered the idea that the foam provides plenty of buoyancy (about 8 lbs per sf). And that the nearly 2 inches between the fiberglass skins provides ample physical strength. If going with an other than original material deck,I might add top gussets crossing the facet joints, and maybe reconsider the bulkheads.

    The plan view is somewhat bulkier and more burdensome compared to a more typical kayak this size, but this is to make up for its greater weight and its greater load. It will be somewhat more stable too.

    There are only three different angles in this boat:

    1.) the horizontal angles between the sides and the bottom, (all the same)
    2.) the vertical angles between the side panels(all the same), and
    3.) the vertical angles where the bow panels and the stern panels join (all the same).

    The last is going to be quite sharp, an almost 5 to 1 pitch. Cutting this accurately is going to be a challenge. One strategy might be to first cut the panel at a right angle, then cut the inner skin at the right distance from the end edge, then try to peel it away. Then, by using a sanding block or surform plane, try to shape the remaining foam to the correct angle.

    Another possible approach would be to cut bow and stern edges at a 1:2 angle, and join them at the inner skins only, with the shorter skins on the outside. Then they could be glassed together on the outside.

    I really don't know how you cut these panels. My guess is that you use circular saw with a fine-tooth ripping blade. Or do you use a mason blade?


    DoorYak.png
     
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  12. TacoFace
    Joined: May 2021
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    TacoFace Junior Member

    Beautiful. And I just now realized how to cut the sharp angles. Skillsaw just through the skin on both sides, then cut the foam with a hot wire.

    ...now that I think of it that might be the way to cut this stuff in general.

    Yes, I've been cutting with a table saw. It cuts very easy and clean, but the sawdust is absolutely horrid.

    Honestly, I might even just handsaw through the skin and then use a wire just to cut down on the horrible dust.

    ...not that I have a hot wire, but that couldn't be to hard to figure out.

    Are you calling this Dooryak because these are door panels? Love it!

    I might even keep this mostly uncovered. Open-top kayak. ...which I guess is kinda a canoe. But, yes, that's a great design.

     
  13. sharpii2
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    sharpii2 Senior Member

    Thank you for the kind complement. Facet boats have become kind of an obsession to me. The vision of sheets of foam sandwich being relatively quickly turned into useful hulls never seems to leave my imagination.

    I am watching a YouTube series about a young couple who are building a 40 something foot sailboat out of mostly salvaged wood. They even made the ballast keel themselves out of concrete and chunks of steel scrap. As soon as the cabin top was built, hull water tight, and the rudder installed, they launched it and moved aboard.

    They have been living on it ever since, and slowly building the rig and interior.

    The series is called "Salt and Tar" if you are interested. They have been working on it for 5 years so far.

    I can only imagine how fast the boat would have come together if it were made of foam sandwitch facets (I would never recommend trying such a thing on such a large vessel. But the dinghy perhaps?).

    If you ever decide to build this kayak/canoe design, please let me know how it goes, by continuing to post.
     
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  14. keith66
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    keith66 Senior Member

    On our local creek a few people have built houseboats from PU foam, they got reject foam from a guy who had a regular contract to clear it from the factory & did a roaring trade to builders & diy 'ers.
    About four hulls were made over wooden batten molds & none have ever gone anywhere, one at least is starting to visibly distort & break up under the weight of the water the foam has soaked up.
    PU foam as a core is as much use as an ashtray on a motorcycle.
     

  15. sharpii2
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    sharpii2 Senior Member

    Actually, there's 5 different angles. There is the first three mentioned. Then there are two more.

    4.) would be the horizontal one between the bow bottom and mid bottom, and

    5.) would the horizontal one between the mid bottom and the stern bottom.

    These last two are different from one another, because the bow and stern bottom facets tilt up at different angles.
     
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