: Thanks Rob. 4oz S-glass sounds like a great compromise between
: strength and weight. I have a tendency to overdo such things
: which is why I wanted a sanity check.

I would second Robs suggestion for doubled layer of 4oz below the waterline. I made a Coho with 4oz s-glass that had a doubled layer on the exterior bottom center hull panels, so it didn't entirely cover below waterline. The interior had a doubled layer to the second chine in the cockpit which is about at the waterline. The kayak was used heavily over three years in tours and lessons, loaded on racks and bumped over docks. On the exterior where there was one layer of 4oz dings would dent the underlying wood, unlike e-glass though the dings didn't result in breaks through the glass into the wood resulting in waterstaining. The s-glass holds together better than a similar weight of e-glass without breaking through the thin hard glass laminate. That said a thicker layer of 6oz e-glass on the exterior would resist dings to the wood better than 4oz s-glass(I had done test panels a few years before) There were places on the bottom of the hull where there was just 4oz s-glass on both sides and dings showed up on the exterior(obvious depression) and interior(whitened threads ) , in another spot where there was one layer of 4oz on the exterior a ding hit a spot right at the edge of a doubled layer on the inside there were whitened threads on the one layer of 4oz on the interior and none at the adjacent edge of doubled 4oz. The area right under the hull that had doubled exterior 4oz and one layer of 4oz on the interior (in compartments) had no interior whitened threads where there was some kind of discernible impact on the exterior.
This is a round about way of saying a doubled layer of 4oz below the waterline where impacts with your entire boat are likely to occur is worthwhile compared to one layer of 4oz.