[65Bowrider]

Looks like balsa squares. If so, that's exactly what we found under our bowrider deck...some wet which caused a soft spot. We removed all the balsa, cleaned, dried thoroughly. Then replaced with several pieces of wood encapsulated in epoxy & resealed the skin with fiberglass strips overlapping the cut seam. Before beginning, build a support brace under the deck to support the crown shape desired until the new deck has dried, then remove brace. Our deck is now very solid.