...for the stem and stern plates in my last SOF. I was going to use it for the keel and chine stingers, but it was a pound heavier than pine for each stringer.

Just for grins, I tried steam bending some for the coaming. No go. It will bend to a point, but not enough for ribs or coamings. Paul's lamination idea would be your only hope for using it for ribs.

I wouldn't even consider mahogany for gunwales unless you want a 50 pound kayak. It's beautiful wood to work with and machines like magic, but it's HEAVY.