a boat from foam-fiberglass laminate panels

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

  1. TacoFace
    Joined: May 2021
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    TacoFace Junior Member

    Yeah, the awkward joining is what I'm trying to figure out.

    ...and yes, having free panels is not a good reason to build a boat out of them. But, seriously, I'm only talking about a rowboat or a kayak sort of thing.

    At this point I'm guessing that it's going to delam after soaking for a while, but I'm still going to test it.

    ...as for the concerns about 64"x22" panels being too small to be worth using... those pieces are larger than one would cut most of the plywood pieces for a glasply kayak.

    The materials I will test destructively under water.

    I am really more interested in the geometry of faceted panels, marine-use or otherwise. I will definitely play with those CAD programs suggested above.
     
  2. TacoFace
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    TacoFace Junior Member

    Ok, just to clarify, you are saying that the foam definitely will absorb water? I was under the impression that some foam materials absorbed water and some don't... is this not correct?

    And, for the fifth time, I'm talking about a day-use kayak not a commercial vessel. The structural integrity of these panels with epoxy is several time greater than an glasply kayak or an aluminum canoe or I appreciate the urge to talk a newbie out wasting time and money on a foolish project, but I think the title of this thread has rendered it obsolete. I'm thinking "The geometry of rigid panels" would have been more useful, and I'm going to have to focus my attention on a couple Geometry discussion board.

    ...I'll post results of my usless test of soaking this material in water to test its absorption rate of being submerged in water by submerging it in water in a week or two if anyone in interested. I am most likely not going to build a box full of water and weigh it every year. Although that does sound fascinating.
     
  3. fallguy
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    fallguy Senior Member

    All I am suggesting is trying to see if it could be used for strip building. Rip the strips at desired hull thickness and plank. Glue them together and see what it does.

    A cedar strip canoe may be on par weight wise.

    make a test panel of about 2' square and say 5/16" thick rips and epoxy a 6 oz skin to each side, wait a week and see if it breaks easily by hand...

    Rumars may be correct, but if you can build a strip hull from them; sure beats landfilling it.

    Not much to lose. An hour or two and ten bux in epoxy n glass.
     
  4. Mr Efficiency
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    Mr Efficiency Senior Member

    PU foam at that density, has less than 100% closed cells, over time with vibration and impacts, further ingress of water will occur, it it is present. The best plan is not to expose the foam to water, until the day your boat wants to sink, and even 50% loss of buoyancy will still see you stay afloat
     
  5. fallguy
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    fallguy Senior Member

    maybe so, but so does cedar have problems when wet
     
  6. Mr Efficiency
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    Mr Efficiency Senior Member

    I wonder whether the best plan with PU is use the higher density, despite the weight and cost penalty, it is reputed to stay dry or drier.
     
  7. Mr Efficiency
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    Mr Efficiency Senior Member

    One thing that is wise to do with poured PU foam, I think, do not break the "skin" of it. That has to help seal it.
     
  8. fallguy
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    fallguy Senior Member

    Nothing a good coating of epoxy wouldn't offer...maybe..read on
    Polyurethane foam is porous, so it should take some water. I'd be curious how much is all. All it tells you is whether full incapsulation is required. That way, you'd know you are required to always seal it with epoxy, for example. ...versus making a gunwhale of the stuff and leaving exposed core that gets damp in a coastal environment...

    But the real test is for shear/compressive strength. You can easily compare compressive strength to foamular 150 pink foam found at HD/others. If it compresses easily; it will delam in a hull easily from impacts. If it is weaker than foamular, that is not great.

    For shear, the fiberglass component adds a web, which would stop, theoretically, a massive delamination, but you still want to understsnd how a canoe hull skin made with your foam cutoff strips would compare to wood.

    Another issue to deal with is if the foam is very porous, it will suck resins bad. Epoxy resins are very expensive, in terms of money and weight and if the material demands an excess of resin to use; that also may make it harder to use.
     
  9. Mr Efficiency
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    Mr Efficiency Senior Member

    2lb/cu ft foam has very little structural value, 4lb/cu ft has limited structural value
     
  10. fallguy
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    fallguy Senior Member

    We've gone around a few times and the web may make it sufficient, for say a canoe, or rowboat, or even solid pontoons when wrapped in glass..

    It is at least worth some exploration.
     
  11. sharpii2
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    sharpii2 Senior Member

    As promised earlier, I'm back to show some of my facet boat designs.

    The first one is a whimsical play on paper boats I made as a kid. It has just six hull facets.
    The next is an example of an eight facet boat that I was considering building. I has a removable bow section, so it can stand on its bulkhead against a 7.5 ft wall with the bow section nested inside.
    After that, is a nine facet version of a 5 by 20 ft mini-voyager concept I have been playing with for several years.
    After that, is a twelve facet version of the same boat.
    And finally, is an eighteen facet interpretation of Joshua Slocum's SPRAY.

    As for cutting and joining the facets, I recommend joining them first at their inside angles, while cutting each squarely. Then mix some filler compound which can be a mostly fairing mix, but close to the density of the foam in the panels. Apply it so it stands proud, so you can sand it down to a nice radius. Then you can apply the glass fiber on top of that as wide tape. This will save you hours of figuring at the expense of buying some expensive materials.

    As far as the limited compression strength of the panels go, I recommend avoiding concentrated compression loads. This can be accomplished by making wooden sub-structures for heavily loaded items such as seats, motor mounts, or even mast steps. You may even be able to make such sub-structures out of the panel material itself, with it standing on edge. Such sub-structures must never end at a facet joint. They should end either four panel thicknesses short of one, or cross the joint by at least the same distance. 6fpaperbt.png PencilJr.png DebGr520.png LolaGrande520.png 18fSpray.png
     
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  12. Rumars
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    Rumars Senior Member

    Yes the foam will absorb water. It's not of concern for dry sailed boats, they don't have the time for it. You can compare it to PU surfboards, same thing. That's why I said that doing the experiment is a waste of time in your situation, the results are irrelevant.

    Your real problem is constructing the boat if the panels won't bend. By the time you cut them in panels small enough to be of use and stick them back together, it's simpler and better to do it as previously adviced, cut one skin off, score the foam, laminate a new skin. That's because you will use the same amount of glass and resin on all the joints, but at least you loose the weight of the factory skin.
    If you are still interested, the way to do it is by dividing the surface into small triangles that approximate your desired curves. See geodesic domes for examples.
    Otherwise you are limited to boats with sharp angle transitions. Things like garveys, prams, and "Bolger bricks" come to mind.
     
  13. fallguy
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    fallguy Senior Member

    Anything wrong with cutting it into strips?
     
  14. Rumars
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    Rumars Senior Member

    Yes, same thing as triangles. The factory fiberglass skins are useless weight, plus you have to sand off the corners. It would make more sense to remove both skins and use the foam alone.
     

  15. ExileMoon
    Joined: Oct 2009
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    ExileMoon Junior Member

    Do you want a stealth boat like F-117?

    Your board is so rigid that it can almost be assumed that it cannot be bent. Then the problem becomes very simple, which is to build a usable boat with a pure flat. You don't expect it to have too good performance, just use it.

    It can even be simplified further. However, considering that the size of your flat board, especially the width, is also limited, you can design more flat boards to combine into more complex shapes.

    flat board boat.png
     
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