hi all
im new to building wood boats. normally I use plastic but this time I want different. I dont know what to use. balsa or plywood? and what thickness? It will be gas powered.

depends on the build itself.
1/4" marine plywood or Baltic birch plywood, I use Balsa for planes not boats. even though lighter its not strong enough.

dont forget to seal all wood with an epoxy type sealer.

Most use 1/8" thick aircraft grade plywood,but other types can be used such as Okoume or even a cabinet grade plywood if sealed properly. If I'm going to fiberglass the outside of the hull I've even used 3/32" plywood as the fiberglass and the resin make up the other 1/32 " to give you near 1/8".

I have tried several different kinds of plywoods, but I have found the Aircraft Grade Finnish Birch Plywood to be of the best quality. The plywood I use is Germanischer Lloyd tested. This means water tested amongst other tests. It is somewhat expensive but the quality is just exceptional. I have also used some 1/4 locally produced Baltic Birch Plywood, which is made with waterproof glue and has passed my own 4 hour boil tests. It is 5 ply as with most hobby grade plywoods. The Finnish Birch Ply in 1/4" is 12 ply, 1/16" is 3 ply, 1/8" is 5 ply. Great quality plywood!