Every so often a question comes up about glass strength vs. fiber orientation. The graph below from Michigan Tech shows that strength is highest along the axis of the fibers, no big surprise. What jumps off the page is how fast strength falls off as the load angle changes. At 15*, strength is only about 60% of maximum, and at 45* strength is less than 15%. This confirms what everybody knows already, it is hard to stretch cloth along either axis of a woven fabric, but very easy to stretch it diagonally. This strength difference does not change after application of epoxy.

Given that we are limited by the width of our glass fabric and the length of the boat, and that most bending forces will be in the longitudinal direction, at first glance it would seem best to align the cloth with the long fibers parallel to the keel. But a twisting force, like hitting a rock on one side of the bow then would hit the glass at a weak point. So maybe the best solution is to use 2 layers of thinner cloth, laid up on opposite diagonals? Some strength would be sacrificed parallel to the keel, but gaining quite a lot in the off-center impact direction.

An additional benefit to using thinner cloth is the ease of obtaining higher glass-to-epoxy ratios. Per unit of cross section, the glass is on the order of 10 times as strong as the epoxy. The resin does 2 jobs, sealing water out of the wood and transmitting forces to the glass. Beyond the minimum to accomplish these two goals, more epoxy does not make a significantly stronger composite.