I did it
Hi Doug,I did exactly this job on my '76 Oday 22. The deck core was rotten under the mast step; the mast was "oilcanning" the deck to the extent that the rigging was all slack and the boat couldn't be used. I sawed out the deck skin, scooped out all the rotten balsa, replaced the core (using solid laminate under the step to prevent future crushing) epoxied the deck skin back on and threw her back in the water. I sailed her HARD this last summer; the rigging remains taught, the boat sails as well as a shoal keel Oday 22 ever will, and the deck under the mast step is flat and hasn't complained a bit. A very satisfactory repair.Question: Did you cut the inner skin out? I have to assume so, how else would you have encountered a space between it and the cabin liner? I did not explore anything below the inner skin; I assumed the inner skin rested on the cabin liner and on to the compression post. Perhaps I was naive, but when I replaced the core and deck and tensioned the standing rigging, the mast came down firmly on the compression post without distorting anything, and again, I sailed under several days of harsh wind conditions without any hint of movement or trouble. I guess I would fill the empty space with epoxy putty if it exceeded 1/8 inch or so, but if it's less than that, there shouldn't be any significant distortion if you just left it alone. That's what the factory did.Best of luck,Clay