: I'm not exactly an expert on composite structures, but I don't see how the
: addition of 'glass strands in this fashion would add any strength.

: It
: would simply be filler. Unless you are bridging the gaps as opposed to
: just filling them, aren't you really just relying on the resin itself for
: strength?

Resin is considered 12 times as strong as the wood that surrounds it, at least that is what the literture of the Gougeon Bros. syas about West system resins. That is a pretty impressive increase in strength, as you have noted. Add glass and the strength increases even more. Much more!

Consider the tip of almost any fiberglass fishing pole. Theyn are typic`ally under 1/8th inch in diameter and made from linear strands of fiberglass bound with a plstic resin. Those tips are strong enough to lift a 5 to 10 pound fish (live wriggling weight) and they flex a lot rather than snap. Of course, put enough weight on them and they do break.

Filling the gaps with caulking adds no strength. Filling the gaps with the equivalent of a fishing pole adds some strength from the fiberglass and resin.

If the strips are 1/4 inch thick and the interior bevel is truly awful at most there would be a groove as deep as the strips are thick, or 1/4 inch. I'd guess the workmanship is a lot better than that, but at points it could go to anywhere from 1/8th to 3/16ths deep. Even with the shallower amount, packing the area with glass would give you a linear strip of fiberglass with a triangular cross section which would be stronger than the typical tip of a fishing pole. Do that for the grooves between 45 strips and you have 44 thin fiberglass stringers which, if you removed the wood completely, would be almost strong enough to cover with a skin and use as a kayak frame.

The thickness of the fiberglass covering on either side of the wood is about 1/32nd of an inch, or about 0.030 inches. The glass packed into a groove 1/8th inch deep would give a strengthening "rib" to that 'glass" skin which would be 4 times thicker than the skin alone. Such an addition would increase stiffness and strength. But it is a messy thing to do!

Usign shorter chopped strands of glass fibers to reinforce plastic resin is commonly done. We make the filleting mix for S&G kayak construction like that. And it works well. Longer strands of glass fibers give greater strength in such mixtures than very short glass fibers. So, that's the origin of the idea of using very long glass fibers laid linearly in the grooves, rather than using a "dookie schmutz" mix of the shorter fibers

: The analogy to traditional caulking is flawed, as my understanding is that
: that is not for strength but for watertightness, i.e filler.

Sorry if that wasn't clearly stated. It wasn't supposed to be an analogy but a contradiction. The usual caulking is indeed for watertightness, and not for strength. However, using the same manner of applying caulking, that is, packing something in the seams, you could increase the strength a small amount by using very strong materials, materials which had a much greater strength than the traditional caulking. In this case you can make the thickness of the fiberglass much greater along the lines of the hull without making the hull thicker. Instead you fill in the gaps with linear glass strands.

Your woven glass cloth which sheathes the wood has more than enough strands of glass running across the direction of the strips to hold them together. Very short crosswise or randomly oriented glass fibers in the grooves would not be as useful, nor add s much strength for the weight they would add.

Anyhow, it is a messy proposition, and nobody does it. Kind of unexplored territory.

Thanks for your comments

PGJ