Have an Explorer 22 1963 - with Wood hull/GRP over. Hull is generally sound but Plywood broken/rotten in several places below waterline in bilges. The GRP is good & plywood seems to be 12mm thick, but looking for further info. expect that its MarinePly or Agba ply but unsure, the frame is rotten in places below deck & believe its mahogany/birch ply construction. Looking for any help, anyone else restored an early explorer ???