Wrapped foam plank

Discussion in 'Materials' started by Owly, Jun 6, 2018.

  1. fallguy
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    fallguy Senior Member

    E1A3DAFE-CCB6-400A-B4A6-3DD0ABB62EB9.jpeg This is a 33' long panel on vac table.

    Vac was just turned on here. The breather will be much wetter after another 20 minutes.
     
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  2. Niclas Vestman
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    Niclas Vestman Junior Member

    Wow, that's extremely good fiber to resin ratio! If I'm not mistaken, it will also be stronger because of the better fiber to fiber load transfer. Hmm... any idea on how much resin is lost in the breather and other places, compared to what actually goes into the part? I guess it will always be quite similar regardles of fiber to resin ratio. More dependent on the individual skill. I would probably waste about twice what you do, because of adding to much when laying up. If really skilled, is it possible to lay up quite dry almost like (prepreg), so the breather only picks up a marginal amount?
     
  3. fallguy
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    fallguy Senior Member

    A great question.

    Falldown is a staggering 30%.

    Infusion would be better.
     
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  4. Niclas Vestman
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    Niclas Vestman Junior Member

    :eek:... **** cr@p on a cracker! Wow, thanks for saving me from a very unpleasant surprise! I'm starting to understand the arguments for vinylester vs epoxy. Great with experienced people sharing knowledge. I'd better go and adjust my cost calculations.
     
  5. fallguy
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    fallguy Senior Member

    I figured I'd have larger pot losses using infusion, but not the case at all.

    Infusion losses are lower.

    Using triax requires more wetout.

    And the foam has its own wetout rate.
     
  6. fallguy
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    fallguy Senior Member

    Really skilled does not mean you have a dry layup.

    A dry layup means you are building garbage.

    The picture I showed has resin losses in several places.

    First, the breather. Despite using a 10mm perforated release film; most leaves via the breather.

    Second, edges get some resin squeeze outs.

    Third, both sides use peelply that takes some resin. The pp is not reusable.

    Consumables in wet bagging are high, but it is supposed to be low tech. Although, I am going to try infusion in July. I used 100 gallons of epoxy for far in the cat build

    Now, I am officially a hijacker. Let's get back to the OP. My apologies.
     
  7. Owly
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    Owly Senior Member

    Lots of good stuff here............ thanks in particular for the linoleum tip. Seems like a very logical way to get a fair surface over a very large area with no joints to fair. Formica doesn't come in huge rolls like linoleum unfortunately. It might still make sense with a good mold release of some sort........ One screw up would be extremely expensive. I'd lose the entire mold, and cleaning up the layup would be a nightmare.

    I'm going to have to go over weight numbers again. The finished weights way too high...... There are two reasons for using sandwich. One is weight reduction, and the other is greatly reduced labor if doing infusion. Finishing the outer surface is a grueling time consuming job. With full length infused panels, this finishing can be reduced to a minimal level of seams only.

    I find it interesting that nobody has responded to the comment about putting rebates in to the foam for joints..... But stupid me.... It finally dawned on me that the foam would not need to be rebated, but rather a layer of some material along the seam that would not stick would need to be to be laid down before the first layer of glass. Perhaps something wrapped in peel ply. Once the infusion was done, this would be removed, leaving a surface that was rebated, and ready for a flush seam.

    I haven't done this stuff.............. trying to figure out the most efficient, easiest, and cost effective way to do it.............

    As far as wood strip, I've built that way before, and it's not difficult, though it is time consuming, but not excessively. I want the hull bottom almost flat in the lateral plain. The only reason for 3D curvature is stiffness. This is a "plastic" boat, not a wooden one. The bottom seems like the worst possible place for fully encapsulated wood.... As long as it stays encapsulated and dry, no problem, but the bottom is what will "take the ground" during beaching. Years of personal experience shows that strategies designed to seal moisture out are even more effective in trapping it inside, and that bothers me.

    H.W.
     
  8. Owly
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    Owly Senior Member

    Here's a direct weight comparison of foam sandwich to plywood with glass epoxy on the outside and epoxy inside..
    Plywood/Glass strength Comparison | Multihull Design Blog http://multihullblog.com/2010/11/plywoodglass-strength-comparison/
    9mm Gaboon weighs 28.6 pounds per sheet. Add 300 gsm cloth to one side, and 600 gsm resin plus 2 pounds for the epoxy coats on the inside, and you end up with 56.6 pounds per sheet.

    The substitution is 19mm foam (3/4") about 10 lbs per sheet. Add 1150 gsm per side of glass and an equal amount of resin, for a total of 4600 gsm in glass and resin, or 30 pounds per 4x8 sheet, for a total weight of 40 pounds per sheet

    ply: 56.6 lbs
    sand: 40 lbs

    The sandwich construction is 70% (rounded) the weight of the plywood

    This assumes hand layup on the plywood without vacuum bagging I assume, and the absorption of the ply, but it fails to take into account any absorption in the foam, or what finds it's way into the channels in the foam. In reality it's probably closer to 80% (or more) if the ply gets a light seal coat first and is vacuum bagged. You are never going to get 1:1, but should be able to beat 2:1 on ply, And in a foam infusion with channels in the foam, it seems improbable that one would get 1:1

    I'm estimating empty weight at 4500 lbs with ply. It's probably not unlikely that I could bring that down to 4000 pounds. I'd like to do away with all stringers and sticks by going with thicker foam and/or more glass. The single possible exception here is the beams. The wrapped foam is an attempt to address the stringer issue.

    H.W.
     
  9. fallguy
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    fallguy Senior Member

    1150 glass on 19mm foam is not right


    For copyright purposes, I will not disclose what is, but you would be overbuilt badly for a 30' boat
     
  10. Owly
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    Owly Senior Member


    I'm inclined to think so too...... I was basing this on what was in the link someone posted earlier: Plywood/Glass strength Comparison | Multihull Design Blog http://multihullblog.com/2010/11/plywoodglass-strength-comparison/
    "9mm ply equals (34 oz) 1150 gsm w/19 mm core". I have another source, and actual designer who has completely different equivalencies. What is clear is that it will be necessary to do test panels and arrive at my own conclusions. Another source equates 9mm thus:
    10mm (3/8") foam with 600 gsm glass outside and 400 inside, and of course resin. That should be roughly 5.3 lbs of foam. That all adds up to a tad over 18 pounds to the sheet, assuming resin weight equal to glass weight. At least by my calcs. 2000 GSM = .409 pounds per square foot * 32 per sheet = 13 pounds of glass and resin + 5.3 pounds of foam = 18.38.
    I don't buy those numbers either......... too light. Of course I would like to dispense with the stringers entirely..... just flat surfaces for dirt to build up on. I don't object to 3/4" foam on the hull sides, but I'm inclined to think 1/2" is probably closer to the magic number. Increasing core thickness (within limits), greatly increases stiffness for a given layup...... or so it appears to me.

    Isn't it fun switching from Metric to English and back again. There is a GSM to Pounds Per Square foot conversion calculator here: GSM to pounds per square foot - Google Search https://www.google.com/search?q=GSM+to+pounds+per+square+foot&ie=utf-8&oe=utf-8&client=firefox-b-1

    H.W.
     

  11. fallguy
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    fallguy Senior Member

    Your own conclusions?

    No.

    A naval architect would provide the needed schedule.
     
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