Cedar

How well does regular, bought-at-Lowe's, cedar work in marine applications?

I have an old 16' fiberglass trihull Seastar Wildcat that I've gutted down to a woven fiberglass shell. I cut out the dashboards and walkthru windshield and I'm going to be taking the bow section and extending it about 30" aft.

To do this, I'm going to need to the new bow section to be able to support about 300lbs, but still be lightweight overall. And I'd like to avoid getting into heavy fiberglassing/molding.

I was considering using the cedar as a framing material behind/beneath okoume planking/plywood. Would this work?

 

I've seen the stuff available from Lowes. It's knotty and over-priced. A 4x4x8 cost at least four times as much as a pressure treated one.
My suggestion is to stay away from cedar for framing because it has little fastener-holding strength.
Fir would be better if light weight is desired. Spruce too. Yellow pine (usu. pressure-treated) would be heavier but very strong and rot-resistant, but you'd have to locate some dry stuff (Try the dump for old house decks that have been torn out and replaced---- there seems to be a lot at least where I live. Hand pick the best. It's also probably the old formula treatment that uses arsenic, so watch the dust.

Alan