Hi guys
I need help for my boat, what is the best building wood for a deep v hull? should i use plywood or balsa? The power plant will be a gas or glow plug.

To me, there is no question on material:
PLYWOOD IS THE WAY TO GO!!!!!!!!!!!!!!!!!!!
Balsa is very soft and, while it does absorb some of the vibration, it also can soak up water like a sponge. To make balsa work, you would have to coat everything with fiberglass to prevent it from having any contact with water. Any place you need to run in a screw would have to have either threaded inserts of some sort or tubing to prevent wicking. If you were talking an electric powered boat, I'd say to go for it but, with an internal combustion engine, go with plywood. In the long run, it will last longer and be better able to handle the vibration and pounding the hull will be subjected to

thank you hydro junkie. also what thickness should I use?

Assuming you're in New Zealand, I'll give the metric equivalents to what I'd use here in the states:
Transom and engine rails: 6mm (1/4")
All other framing: 3mm (1/8")
Skin: 1.5mm (1/16")