Marine Grade Plywood?
For any marine structural hull component, the wise builder will settle for nothing less than Lloyds registered/approved BS 1088 Okoume plywood. It is stable, has met stringent manufacturing standards, and has an excellent strength to weight ratio. Both the wood used, along with the glues, are rot and mildew resistant, water, steam, and boiling water resistant. It curves easily to form a nice hull shape if handled correctly. I replaced a number of stringers and a couple of bulkheads with it on my sloop and was quite pleased with how easy it was to work. My sheets were made in Greece, and carried the Lloyd''s of London certificate of inspection. 3/4" 4'' X 8'' (or the metric equivilant) ran about $220/ea. delivered.