I'm toying with the idea of building a Ganymede from plans. A local lumber supplier stocks Joubert brand marine okoume plywood. It seems that CLC plans call for 3mm, 4mm, or 9mm ply, but when I asked the guy about sizes, the answer I got was kind of "subjective". Since Joubert is an English company, the sizes shoud be metric? I saw some pieces that were exactly 3mm, and others that were exactly 5mm.