Marine fir is susbstantially heavier and less flexible than okoume. It also checks unless it's covered with 4 oz or heavier glass. Whether it's flexible enough for your particular boat depends on the boat's design. Long gentle curves should be OK. Something like the WD12 would be a lot of pain, soaking and possibly steaming (and maybe words they don't use in the Bible).

The good news is that fir is a lot more rot resistant than okoume.

Good luck,

Laszlo

I have almost finished a non-CLC designed ten foot skiff. The  plans called for 1/4" / 6 mm Okoume. I happened to have some 3/8" fir plywood kicking around. It was much more difficult to work with towards the bow where it took a lot more force to pull it all together. I know there were some voids in the plywood. It turned out "OK" but I'll never do it again. It's about 50% heavier, but could be stronger, but there are lots of boats built with 6 mm Okoume that are more than strong enough. It was a "learning" project. I'm itching to get going on one of the three sets of CLC plans that I have... with BS-1088 Okoume.