Wet Core
David, Been there before.1) Dry the area as best you can, tarps, heaters that kind of thing.2) Best to drill several, many-depends on how far it's prgessed, holes WITH A GUIDE! DO NOT DRILL THROUGH THE 2ND LAYER OR OVERHEAD.Before no 1 above so it will in fact dry better, but some do it the other way round too.3) There is a method of using a bent nail in the drill to 'clean' out some of the rotten wood, not necessary, but good results have been reported.4) Use penetrating epoxy resin, or vinylester resin to permeat into the deck core.Check with the foreman at your local boatyard or get the book 'repair of fiberbglass boats'Good luck this is NOT rocket science and repair of blisters is much harder and easier to go wrong.