The wood gives the boat its shape and color, but not much strength. The thinner plywood should work fine, but you might want to add an extra layer of cloth on the entire interior of the hull.

Thanks Twofootartist. 

I know where I will be getting all my Okume now. I am addicted to boat building now and plan to built another boat once I finish my C17.   The MC 16.5 is in my sights to buy plans next.

I'd be a little concerned about the additional weight of an extra layer of glass and epoxy vs. just using the appropriately spec'ed plywood. It's also marginally more of a pain to glass the interior neatly without getting bubbles, puddling, etc. Especially if you were trying to get the glass up into the pointy ends of the bow and stern. Maybe you could glass the panels before stitching them together? I don't know, seems like one of those short-cuts that could end up being more costly than it was worth in various ways. But maybe that's just me....

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eric