I'm assuming the mold is for glass boats.

It sounds like the gell coat is lifting from the under lying glass on the mold.

I can thing of a couple of reasons for this:

1) you are pounding the boats loose from the mold with a rubber hammer of sorts. Normally the boat is coaxed out by hand or compressed air is normally used.

2) The mold was made with a lot of internal stress'. This could be due to the use of polyester resin with not enough glass reinforcing. Polyester has a large shrinkage factor as it cures.

The bottom line is that one way or another you will have to fix this mold. If it is fixable. To fix the gel coat cracking will likely be as big a job as making an entire new mold.

Matthew