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Old 04-18-2017, 06:27 PM
messabout messabout is offline
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Think of the foam sandwich as if an I beam or wide flange structural element.. The part of the beam that contributes most to the strength of the beam is the lower flange that is farthest away from the load which is applied to the top flange. Note that the flanges are bearing the bulk of the load. The web part of the I beam only serves to hold the flanges apart.

It should be evident that the foam component of such a layup delivers the function of the beams web. That implies that the foam had best be fairly rigid and capable of absorbing a moderate compression or bending load. Pick your foam carefully. A material such as Klegecell is ideal for such an application. Unfortunately foams like Klegecell and similar ones are both heavier and much more costly than foams found in the big box stores.
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Old 04-18-2017, 06:47 PM
upchurchmr upchurchmr is offline
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That's no problem at all.
Just stick the foam in, Glass over it with epoxy.
I "think" that polyester resin will melt the blue foam.
I also understand that extruded blue foam does not absorb water to any noticeable amount.
Par's issue about the boat not being supported will and being bent when you do the repair is a real issue, cause you could get a permanently bent "fixed" boat.
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Old 04-18-2017, 08:06 PM
Sparky568 Sparky568 is offline
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Location: Northeast USA
I understand the sentimental value as I inherited my Dad's boat and kept it for ten years after his passing but was more work to rebuild than I had time effort and money at the time. My condolences on your loss.

After seeing the pictures I can see your "in it" too far to say forget it. I know Cape Codder boats are still in business.

Not too many boats from your era can say that. Might be worth a call over just to see what they recommend and why, as I'm sure they have done numerous re-builds. I would replace what came out but I also try to think out of the box at times. Wish you luck.
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Old 04-18-2017, 10:36 PM
Resurrection Resurrection is offline
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Sparky 568,
I believe I did read somewhere that epoxy resin won't melt this foam when it's curing but I wasn't sure.
I like the Dow XPS for it's very low moisture absorption and it's price, mainly.
However I know that even though the epoxy bond is better than polyester resin, it's much more expensive. Also, once you go epoxy you can't use polyester over it, and with as much glass work as this boat needs, going all epoxy would be hundreds of dollars more. Still might be a better way to go.
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Old 04-18-2017, 11:12 PM
Resurrection Resurrection is offline
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My thoughts on meeting the load and stress requirements are to retain but reinforce the existing stringer skins internally and externally , then use the foam to construct lateral beams that would be formed and glassed in between the stringers from side to side and from the bottom inner surface of the hull up to, and level with, the bottom of the deck.

In that case, wouldn't the bottom inner surface of the hull act as the lower flange of the I BEAM according to your analogy, and the top surface of the glassed-over foam beam act as the top flange of the I BEAM , with the vertical mass of the fiberglass on the sides of the foam beams bearing the vertical loads ?
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