Keith, No the core in our boat was taken care of by the first owner. He did pattern drilling and then filled the rotted wood with
epoxy. Which is a good way to fix the deck but where he drilled the holes they poped the
paint off after a few years so I took and sanded the deck down to the glass and added a layer of 10oz glass then repainted, to keep the holes from coming back. Depends on how bad your deck is but doing the repair from the top is the only way to go. If you have large areas that need to be fixed you will be better off cutting the skin off and replacing the core. Where are you located and how bad is your deck?
Scott