crack

The companionway hatch cover on my Victoria 18 is cracked and needs repair. I believe the construction of the hatch, like the deck, is balsa-cored fiberglass. I'm looking for advice on material and technique for a strong repair. What weight of glass cloth? Do I replace the core? Etc.

A young friend just bought a Ericson 29 with an encapsulated keel. A surveyor (post purchase!) noticed a crack in the glass on top of the keel, in the second (forward) access hatch. He had a theory that maybe some water got in and froze making the crack, but admitted he didn't have a clue. Don't...