IT HAPPENED TOI ME
I had the same problem, I made a left turn out of my slip and the cables jumped off the metal sheaves, no steering yet powering up the channel, fortunatly I ran into sea grapes, tied up and removed the cables off the quantrant, and placed my emergency tiller in place , turner around and got her back into the slip. I marked the floor to see how far and wide i could use a 7" dia, rotary saw, set the blade at 1/4" depth, only cutting the top surface, lifted the top skin, and started removing the deteriated ply wood, wich is 6" squares, i soaked two pieces of 3/4" ply, in resin, acetone and hardener, with a 12" dia. hole where the pedestal go's, that area i filled with 14 layers of triaxiel mat glass, each had a 4" dia. hole in the center, filled all the gaps and seams with chopped glass, relocated the top skin with a lot of screws, after drying, removed the screws filled the screw holes and seams, and sand painted the cockpit sole, can't tell if it were opened or not, good luck.