Epoxy over XPS method

Discussion in 'Boatbuilding' started by mvoltin, Nov 16, 2018.

  1. fallguy
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    fallguy Senior Member

    Someone else mentioned the ca glue. I am quite sure it is incompatible with at least the san.

    I'd say the xps uptake is probably 'de minimus' which more or less means only enough to wetout with the method used. Corecell M, for example M80 is 0.71 kg/m2....I use 0.65 because my layups are really too wet already and we are rolling it on. If I had to wager a guess on the xps; I'd plan for 1/3rd, but expect it more like 1/4. So say 0.25kg/m2....aiming for 0.15 eventually

    Gurit M is really resin thirsty stuff. The surface is very rough and this drives the uptake.

    I was wrong on the gauge. I vac bagged the xps at 10 psi. Sorry about the inches. I get the two crossed up in my brain. The gauge is even hard to see under the table! 10 psi is as low as my method of metering allows...10 psi crushed the edges, but honestly, I probably did not do a great job setting up the bag for a 2" edge. I am merely pointing out it will crush/compress rather easily at 10 psi. San, of course, with 6 times the compressibility shows nothing at 30psi.
     
  2. fallguy
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    fallguy Senior Member

    If I do this for the curved hardtop and I may, I will build the panels first; glass the topside with vac and the bottom side by hand..

    Might be a bit tricky to keep it all together on a mould..I have visions of a sticky mess in the trash can.. haha

    More seriously..I will need a way to temp bind the san bottom layer with hardpoints installed to the jig; then as I go to bind the 1/2" xps to the jig; twice; then the final san...the whole while making sure the vac can do its thing...hell of a lot easier to do flat..

    Any ideas are welcome. I will add pics of the work. The hardtop is roughly 42x?48?"
     
  3. Rumars
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    Rumars Senior Member

    I have no doubts corrugated fiberglass can work as a structural element. It will take some FEA and some coupon testing to achieve the desired result but it can be done. What I don't understand is why the need for XPS. If the foam serves no structural purposes just leave it out, it only makes the panel heavier. I can only see it used if it is necessary for production (as a former).

    XPS is a good option as a substitute for honeycombs in non structural applications where weight is not critical. That's because it is simpler to glue a continuous sheet of something instead of one that is mostly air.
    Take fallguy's hardtop for example. I would slice the 12mm SAN foam in half and glass both sides of the resulting 6mm sheets with light cloth (in a mold if it has to have compound curvature). Then I would glass the perimeter and center beams and any hardware mounting points separatly. Finally glue everything togheter with thickened epoxy using XPS or EPS to fill the remaining spaces. Of course it will be heavier than a honeycomb cored panel, but simpler to produce.

    For a hull XPS makes one jump to a lot of hoops. First it only takes epoxy or special styro safe poly. The price difference between polyester resin and epoxy alone can pay for a lot of PVC core. If one has to use epoxy resin, wood cores are cheaper.
    Second it has such low shear strenght that one has to make monolithic objects (surfboards or log amas) for it to function. Even there it can only take thin skins. If one tries to make it structural with tricks like corrugations and such you can normally remove it from the equation and arrive at the same result.
    XPS seems cheap and lightweight. By the time you make it usefull it looses both advantages.
     
  4. Eric ruttan
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    Eric ruttan Senior Member

    It seems obvious, right?
    I was only able to find a few papers or even discussions on it.
    Because it is the cheapest/lightest vacable and infusable foam. Do you have a cheaper, lighter foam?
    I cannot make the corrugated fiberglass without. but I would love to hear your idea.
    Which it is.
    As noted above, its the lightest thickest core. well, with a few other limitations. I am not interested in a hollow hull structure. I prefer a hull that floats, but different strokes. Do you know of a lighter, vacable, cheaper foam?
    For the reader; here is a floating boat trying to be sunk Multihull Structure Thoughts https://www.boatdesign.net/threads/multihull-structure-thoughts.62361/page-69#post-875927 Do you think it would be hard to sink if the hull was hollow and not foam?
    I do not plan for someone to shoot my boat, but I think I feel better knowing they can.
    If assume a simple curve, you make a simple mold of bent ply, lay outer cloth, and hot wire XPS, lay in the corrugated cloth, lay upper cloth and infuse. its new and cool and light. And imagine all those likes on boat design!
    not hoops, trapazoids. pay attention!
    which is, of course, the very best glue.
    It seems to me they are basically the same price. I think in bulk they are about 10% different, right? Tjats a big deal to a manufacturer, but less important to me. Epoxy does not stink like hell, and I can use that awesome XPS foam. And people are saying its the very best glue.
    Not for me. Where can you get 15$ sheets of 3/4" wood cores that weigh less than 25kg/m^3? Also wood rots.
    what a weird statement. So you believe you cannot make hollow things with XPS? Like the picture of fallguy's tub above.
    what a weird thing to say. like you cannot laminate heavy skins over it? Or do you mean structurally it cannot take thicker skins. Because 700kps XPS is approximately H80 equivalent, so should be able to support any skin it can. Not that any of that matters, because this is not that. pay attention.
    Feel free to submit your idea for a lighter 80mm core.

    That was kinda fun
     
    Last edited: May 24, 2020
  5. Rumars
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    Rumars Senior Member

    I do not know the meaning of the word "vacable".
    You will need to make some panels and test them to see their physical properties and price compared to mainstream boatbuilding foams. I will gladly accept I am wrong and XPS is a great option for boatbuilding if and when you can proof it.

    P.S. You can make corrugated fiberglass using removable and reusable formers, hand laid or infused. I understand you want the foam for flotation but that is something else.
     
  6. Eric ruttan
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    Eric ruttan Senior Member

    ha, ya. i meant that it is able to handle vacuum. In that it can hold shape under 1 bar. Like EPS would be cheaper, but it is hard to find stuff that wont deform under vacuum. so any former foam need to handle 15psi vacuum with ease.
    Price is easy. XPS is like 5$ a meter at 25m thick, and glass is , what 5$ a kg?
    The testing is hard. What kind of tests would you do, or except as valid? Because one problem is the making of a 2" corrugated glass panel seems not hard, but how to test if it has valid properties, because no one wants to pay for a H80 2" sacrifice to race against it..
    If you had a set of criteria you think a 2" cored panel should do, that would be helpful. Like now I need to be able to bounce a driven golfball off it.
    If you have ideas, I could make a list.
    totally reasonable. but what proof would you need to take you interest to the next level?
    ya, i am not looking for a race boat.
    I had thought of making a corrugated mold to infuse glass sheets on, but with a hollow core I cannot infuse the final skins on, so whats the point? Also I lose insulation.
    But it might be cool for fallguy?
    But I want to infuse the final hull halfs, in a boat shaped like detailed above, so just a corrugated glass sheet is useless.
    If one had corrugated glass sheets, how could you see them being used? just vac bag them one side at a time onto wet layup?
     
  7. fallguy
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    fallguy Senior Member

    All of this is great fun, but ultimately I think you are both somewhat right.

    If you have the resources of Dow Corning; you would think if they believed they could take the marine foam industry on; they'd have done so.

    They have not tried.

    But for things like insulated hardtops where the sun doesn't bake or a heating system warms the roof without high losses or a table or even a 2" thick deck or a livewell, there seems to be rational use.

    A 2" thick hull would be something specified in a rather long yacht. The cost budget for such a beast is typically say a $1,000,000 to start to say $3 mil. Let's say you are talking 120 footer or somewhere in the neighborhood of 15 panels long by ? 16 panels wide or 240 panels of 2" material. Cost those out at say 400 a sheet and your core cost is roughly $100k. Noone budgeting that ride is going to consider for a fraction of a second trying to save 50 grand filling the tweens of san core with xps...

    This is not meant to burst bubbles, but merely point out rational use.
     
    Last edited: May 25, 2020
  8. Rumars
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    Rumars Senior Member

    For me it is pretty simple. Take whatever cored panel you like and try to emulate it's properties. For example if your favorite designer specified a panel of 600g/sqm fiberglass/epoxy-10mm crosslinked PVC foam-600g/sqm fiberglass/epoxy this panel will have specific values for strenght, stiffness, impact resistance, point loading, etc. What you need to do is make a panel with XPS that exhibits the same or higher values in all categories. How you achieve that is irrelevant, I don't care if your panel ends up using 80mm foam with 200g/sqm or any other thickness and layup. The thing is that in order to be able to exchange one panel for the other they must have at least the same properties. Then, and only then we can compare weight and cost, otherwise we are comparing apples to oranges.
    Testing is done by materials properties labs on dedicated machines using approved industry protocols. Hitting the laminate by hand with hammers or golfballs is not relevant testing since you do not get numbers out of it.
     
  9. Dejay
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    Dejay Senior Newbie

    I just meant this picture as an example of a rectangular hull, like what you mean also.
    HarryProaCruiser50Cruiser-50-003-e1511625931382.jpg

    I think the big problem is going to be point loads like hitting a sharp rock. You will need to make the outer fiberglass shell thicker than with H80 foam. Of course you can also repair damage but that is problematic and possibly risky. There is also hydraulic erosion if you don't notice it. So I've mostly resigned myself to paying for proper foam for the hull and structural elements. Everything near or below the waterline. Or maybe build out of wood.

    But for the large "tiny house" I want to put on top of my solar power trimaran I'm still looking for the ultimate solution.

    I've also considered something like a giant CNC sewing machine that makes holes in an XPS sheet and threads fiberglass tow through it. You'd end up with something similar to drop stitch inflatable but with thick resin infused tow. That would take care of any potential delamination.
    If you could angle the holes with the thread you could also make tetrahedrons or girder structures. No clue how that would compare to hexagonal or corrugated webbing. Potentially the stitches with tow would need to be thicker but could still be lighter. In general I think towing is cheaper than cloth.

    Of course now you'd need to build some kind of 5DOF CNC sewing machine. Actually it would only need to be 4DOF and could be made out of light and cheap 3D printer tech.
    Advantage would be that you don't end up with strips that you'd have to place and weave with cloth by hand. You could generate all the needed sheets beforehand and have the machine sew and cut the XPS sheet into the right form.

    Hmm theoretically such a machine could have quite some interesting possibilities. You could cut / mill out kerfs out of the XPS sheet that enable it to be pulled together into compound curvature with the stitches. But then it gets really complicated haha.
     
  10. Eric ruttan
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    Eric ruttan Senior Member

    Thanks
    Why is that a problem?
    Why do you think so?
    How is it risky?
    I think no, but I ask for you to explain your fear of this.
    As you wish.
    Oh god no. Boats should not rot.
    What are the attributes of 'ultimate'?
    If you are CNCing tow through foam you are in the same place as corrugated. You do not care about foam delamination, because all the strength is in the tow. the problem is the tow column is not very strong, so you need lots of them. Then it becomes cloth, and you get to corrugated glass. Ask me how i know...
    My thinking was, once you get the stitch density enough to have tow columns start supporting each other, like cloth does, you have basically needlepoint-ed the foam in two.
    CNC knitting machines exist, but I could not find a CNC "sewing machine", although modern sewing machines certainly qualify, they have neither the large format we are discussing, nor the rotatable/angleable needle and shuttle function, nor the ability to penetrate 80mm of material. A sewing machine has just as complicated shuttle as head. Said shuttle would need to move to catch the needle and know precisely where it will come out. Apparently strength and stiffness is needed to accurately place the head and shuttle. Its one thing to know where the needle will come out when going through cloth over a short span when held in a steel 'U'. shooting through 130+mm of foam, on an angle, with a 150+mm needle, in the middle of a 4x8 sheet of foam, and knowing where it comes out so the shuttle can thread it, is a challenge. The hole in the foam is big, as the needle needs to be. The hole will close, but you have a big split in the foam. I also saw a fair amount of tear out in pushing the needle through and pulling it out. I imagine a lamination lube could be found, or a tougher (more expensive) foam but it is yet another complication.

    Now one could simplify with just doing vertical stitches, but then the foam still needs shear strength, I think.

    But, even if you figure that all out, I found the foam very weak to move and prone to breaking when hand sewn. Which lead me to cloth.
    people pull flat simple curves into compounds with hitch straps.

    I would like to note the drawing of small trapezoids above are kind of a worse case. If we had some sort of performance numbers we could make the sticks larger and reduce the fiddlyness of laying sticks, which I do not think will be too bad, but others object to.
     
  11. Eric ruttan
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    Eric ruttan Senior Member

    Burt Rutan did not have said resources when he started building plastic planes.
    Why would they? They supply said industry anyway and it is peanuts to their market share
    You have not engaged the rational use scenarios suggested above. While a traditional build technique may suggest 2" equals something, if one can drop the cost of said 2" hull an order of magnitude, then it makes it way more accessible to home builders. Then said thickness can have other purposes.
     
  12. Eric ruttan
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    Eric ruttan Senior Member

    You miss the point of my question. What properties would you like it to have? unless you don't know those properties, then I retract the question.
    It is easy to say 'needs be the same'. It is informative to say, in these specific ways it need to be...
     
  13. Rumars
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    Rumars Senior Member

    I don't understand what you are asking me. How to determine hull scantlings? How to calculate a composite sandwich panel?
     
  14. fallguy
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    fallguy Senior Member

    Let me repeat myself.

    A cost budget for a large boat requiring a 2" thick hull is significantly larger than the cost of the core. Like WAY larger. I told you this and I will tell you again. I am not convinced using xps for a hull makes economic sense.

    I spent roughly 10k on cores for a 10 meter cat with a cost budget 10-15 times that and I am unpaid lead. If I were paid, my core costs drop to 5% or less. And that is rather poor pay. I digress. Point is no way is anyone with a cost side budget of a million gonna shirk on core to save 5% or even 10%. It ain't happening because it is foolish.

    I think it makes some sense for my hardtop. And could for a thick deck that needs the cube rule and insulation against the cost of thick thick san core.

    I think Groper said he would use xps as a core in a plywood sandwich for a 20 meter build. I can almost see it there...still don't like the shear business, although you know a few strategies.

    The whole thing about rational use is simple. I do not want to take unneeded risks that it will fail. I can afford a hardtop failing, or a table, or a countertop, or a livewell. Not the hull. I am still worried about my hulls being a bit light on resin! Last thing I want to worry about is whether xps will shear away from the glass.

    I am building two dingies in the next 12 months. I won't even risk using xps on them.
     
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  15. Dejay
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    Dejay Senior Newbie

    You ask a lot of questions ;) I'm a novice and still need to learn about structural engineering of laminate and foam core so I can plan better, and I need to get my workshop sorted to start doing experiments. So I preface all this is just from my uneducated opinion and limited understanding. And like you I'd also love to find a new ultra low cost way of building.

    I think the problem with XPS for the hull isn't the global loads but the local ones, like mentioned in this thread: Structural design - some brief on approaches (unfortunately that thread escalated quickly haha) local loads dominate in small boats below 25m. Footsteps, bumping things into walls, dropping things on the deck, stuff crashing into your hull.

    The corrugated mesh solve the problem of delamination and loads over larger areas I believe. But point loads it's basically unchanged from fiberglass on XPS without the corrugation.

    So with a weak core, you need thicker laminate to compensate and spread out the point load to avoid damage. That is why you need far less fiberglass on wood because wood is basically the strongest core. So basically with XPS just because of the point loads you end up with the same laminate thickness that you'd need for a non foam core boat. I'd love to know what Rob specifies for the hull bottom.

    Hydraulic erosion is basically a hole below the waterline where water gets in and pressure from waves leads to hydraulic pressure effects destroying the foam. So basically foam below the waterline also "rots" just like wood if left untreated. This isn't a huge problem because the area below the waterline is limited, but best practice is to have rather thick laminate there.

    And of course the risk is damage. Just because your boat wouldn't sink doesn't mean it wouldn't be a catastrophe if you get a hole in the hull. A collision with some flotsam or buoy or another boat or a rock when grounding on low tide. So worst case it could cost you your live, best case you have a lot of hassle repairing and maybe hauling out at a boatyard.

    I think Rumars suggestion to build a test panel and compare it to what Rob specifies is a good one not a brushoff. Because it doesn't require strict standardized tests. You could design something like dropping a metal rod straight onto a test panel from a specified height and compare results. This is easy to do and leads to objective answers if it's good enough.

    ---

    And again I'd love to find a way to build cheaply myself. Even if I shell out for 20mm sandwich foam core material I haven't found a good (ultimate) solution to how to vacuum infuse insulation in between the structural foam and fiberglass.

    I think the best solution might be to have a sandwich of fiberglass surface, 3-5mm structural foam with flow channels, insulation foam and the same on the other side. At vertical intervals you add more of the structural foam with flow channels as ribs. All the flow channels would need to be aligned that resin can flow around the insulation. Instead of corrugated fiberglass webbing you'd get rectangular cases of proper structural sandwich material around larger XPS sheets. So you'd have 4x2 slabs of thick XPS surrounded by ribs of composite. The XPS serves a purpose to add stiffness by widening the beam and as insulation and still allow you to vacuum infuse around them.

    So you save money on structural foam using only thin sheets, get impact resistance, insulation and a stiff wall.
     
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