I built a Yare in '95 out of Chris' book, with a 3mm deck, no glass underneath, no glass on top, only tape at the seam. After 2 seasons and frequent wet reentry practice the rear deck popped the seam on both sides. Even with the camber, unreinforced 3mm okoume must flex too much. I redecked last summer with 4mm, 4 oz. glass top and bottom, and it's up to the task now. Quite a bit heavier, but now it's kid-proof. I suspect that 3mm would be perfectly OK if people weren't crawling around on it all the time.