Re: repair on a Santana 20
That stanchion damage looks like the core has rotted away. In order to fix it right you will need to cut away the glass either under neath or from the deck side until you find solid coring. Then you should replace the coring with something suitable ie: same core material or marine ply of the same thickness, then re-glass. As to where the deck pulled away from the hull side you will need to grind and re-glass both the deck flange and the hull flange in order to make it structurally sound. I would grind the whole inside edge along the deck to hull flange to bare glass and lay glass tape in there to make a single structure, that way you won't or should have to worry about the joint tearing apart like that again. Neither of those 2 stops can be fixed with just putty, and be able to stand any stress ie: flexing of any kind for long.