Travis: Now that I'm an expert on bias cutting (ha, ha) I'll try and answer your question.

If you need to cut a piece of 'glass to tape a seam (especially a sharp one like on the bow) then it helps to cut it on the bias, with threads not parallel and perpendicular to the seam, but in a cross-hatch pattern relative to the seam.

As for cutting out a piece large enough to cover the entire hull, the bias may be academic because the width of your bolt of fabric probably won't give you a choice of how to cut and orient the threads. Besides that, except for sharp seams, fiberglass cloth is pretty good about adapting to the gentle contours of a kayak so you shouldn't have any problems.

Hope that helps, Peter