: Nick mentions in his book using 1/2" plywood, but Vaclav mentions in his
: book to use 5/8" or 3/4" (he thinks that 1/2 is too thin). Does
: anybody have any insight on this topic ?

I've used 1/2 material for a lot of boats now and have never had any problems I can attribute to the forms being too thin. I'm with Jay, use what you can get ahold of. Most of my early boats were built on Textured-111 plywood siding left over from building my brother's garage. Over the years I've also used MDF, particle board, MDO, CDX plywood, birch ply and OSB. I've always used 1/2" material, because that is what I seemed have on hand. If you have to buy something, MDF, CDX or OSB work fine. More expensive material is not necessarily better, just more expensive. As Jay says, lightweight is good, CDX is probably the lightest, but even it is pricey these days.