My C&C30 had the same problem. The job is not as simple as it looks. I cut out a piece of the fiber glass floor in order to properly glass in the new frames. I glued 2 pieces of 3/4" marine grade mahogany plywood together foreach frame to get a frame thickness of 1 1/2". They were glued in place with epoxy resin and completely encapsulated with glass and epoxy. One must somehow mark the location of the oak block that supports the mast shoe to make sure it ends up in the same place after you installed the new frames. I must have done this job at least 10 years ago and the wood still looks as new because it is completely rapped in fiberglass. I bolted a plywood double underneath the floor to put the piece I cut out back into place. If done right this repair will last as long as the boat.
Good luck.
H.C. Fierz hfierz@home.com Kingston Ontario

There have been only two areas of concern on our 1980 C&C 30.
The first is the mast step problem which you have seen documented. I did a quick fix on that after taking the oak block off and discovering that the top center of the cross ribs had crushed down a little which allowed the block to settle a little. I cut some stringers out of teak or oak (forget which) to cap the cross ribs with. They span the entire width of the stringer, spreading the load. They have solved the problem for this past year, the mast step is still where it was installed. At the same time, I put a small automatic bilge pump in the lowest part of the bilge - right under the mast step. It keeps that area dry and keeps the cross stringers from getting waterlogged. So far, so good. The best fix which has been posted to this thread is the fellow who just poured the whole area full of resin. He made a tunnel for the very bottom (to allow water from the bow area to get through) and a column for the forward keel bolt and filled the rest up..... I plan on doing the same if there are further problems.