Vacuum Bagging On Plywood and Balsa Permeation?

Oh, you mean a sandwich of plywood/foam/plywood?

gonzo said:

Oh, you mean a sandwich of plywood/foam/plywood?

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No. I am just making an analogy. A sandwich of light plywood, core, glass is not dissimilar. The real question is will it stay together under extremes of heat or impact, and if so, how, etc.

I think the concept is interesting and not just to be brushed off. I wonder if @rxcomposite has seen it or even built it.

I am mostly curious..

There is a huge difference in material characteristic between foam and plywood. If we are talking about a plywood core and not foam, then it is a different discussion. The contribution to longitudinal strength, the compression and shear strength of plywood are vastly higher than foam.

But many boats are being built with foam and carbon. The concept is not novel. So, how?

I agree many boats, airplanes, etc are being built with carbon and foam core. However, they are not built with carbon on one side and e-glass on the other. It makes sense to mix fibers when they are properly engineered. For example an s-glass laminate with carbon or kevlar as reinforcement on highly stressed areas.

gonzo said:

I agree many boats, airplanes, etc are being built with carbon and foam core. However, they are not built with carbon on one side and e-glass on the other. It makes sense to mix fibers when they are properly engineered. For example an s-glass laminate with carbon or kevlar as reinforcement on highly stressed areas.

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Gonzo, You are just WRONG that "they [boats] are not built with carbon on one side and e-glass on the other" as I've said now 3 times.. Go read page 4 of http://www.morrellimelvin.com/brokerage/listings/rapido60/rapido60_fulldescription2017.pdf . It says quote "Hull and deck E-Glass outer skins, carbon fiber inner skins, vinylester, epoxy, divinycell foam sandwich construction." If you don't think this is properly engineered, maybe show us some evidence, like calculations instead of just making claims that the core will fail. I'm sure M&M engineers would disagree that their design is not properly engineered.

gonzo said:

I agree many boats, airplanes, etc are being built with carbon and foam core. However, they are not built with carbon on one side and e-glass on the other. It makes sense to mix fibers when they are properly engineered. For example an s-glass laminate with carbon or kevlar as reinforcement on highly stressed areas.

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When you laminate Carbon and S-glass together, they have equal Strain by definition. The Carbon will fail when the S-glass has barely taken any stress ,because Carbon has a much higher modulus. As you can see by the figure, the S-glass is only at ~700MPa when this mix of Carbon and S-glass fails. So, I do not agree that it makes sense to reinforce S-glass with Carbon since you essentially have to size the Carbon to take nearly all the load and the S-glass is just waste.

I think we should keep a sense of proportion about construction methods.There may be a few hundred boats built of carbon each year and some of them may incorporate glass or other fibres.Which becomes insignificant compared to the tens of thousands of boats that are produced from only glass.If anything,I would hazard a guess that this project might turn out lighter if the plywood was left out and an all foam come used.Which would have made the laminate lighter,but required a fairly thorough armature over which to lay the foam.Now we have the apparent conundrum that vacuum bagging the outer laminate over a possibly sub-optimal core is considered desirable.Yet wet layup with no vacuum probably wouldn't add more than 5-6Kg for a lot less work.I think some test panels and physical testing might be a good idea-both for laminating practice and to establish some solid data.

zstine said:

When you laminate Carbon and S-glass together, they have equal Strain by definition. The Carbon will fail when the S-glass has barely taken any stress ,because Carbon has a much higher modulus. As you can see by the figure, the S-glass is only at ~700MPa when this mix of Carbon and S-glass fails. So, I do not agree that it makes sense to reinforce S-glass with Carbon since you essentially have to size the Carbon to take nearly all the load and the S-glass is just waste.
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You disagree with all the designers generating advanced designs and on the cutting edge of technology. Their successful designs are a fact, not opinion.

For what its worth, I was the one who mentioned plywood, for the sake of discussion only.

I find the idea interesting and I see little reason it won't work. I understand the problems with carbon.

My questions are about point of failure and post cure or heat extremes.

I also read that carbon boats were louder inside. Apparently wave slap becomes more like wave ding.