I dont know what the extra reinforcement is composed of as the failure of the panel occurred at the top of this "cored" portion at the turned in flange. The rip was in an arc just above the core and was definitely solid glass. Basically, the upper gudgeon was punched into the stern.
Mark's 3/4" thickness is probably a close approximation.
It interesting the way we find out about the construction/composition of the boat.
