Louis, that whole thing about I-beams is true but a wee bit on the simplified side. There's a few more additions into the equation to really get a good strength-to-weight ratio, ie,there's a point that the web (the wood in this case) becomes too thick and the curve turns down. Now that was probably more info then you cared to know...the bottom line is that 1/4-inch is a starting point from which wood comes off while fairing. Too much is a problem in some areas...The yak I'm building right now we're purposely sanding down to 3/16-inch,less in certain areas of the hull and deck. We're going to lay two layers of 6-oz biaxial cloth inside the hull, and a series of reinforcements under the deck. This is an experiment of sorts, but the result will stronger then the typical fiberglass kayak out there. Keep in mind that in most cases the strip built yak will be stonger and lighter then the typical store bought glass yak. Now, back to the thin areas issues: where exactly do you suspect are those thin areas? The centerline of the hull and the curve of the deck forward and aft of the cockpit are subject to substantial stresses and would require another layer of glass. regards TnT