Just fixed a few of Mariposa's broken ribs. I used American White Oak (from Robins), 6mm thin and laminated in a jig to the desired curve plus a bit more. I had to steam the oak to get into my jig.
I cut out scarfs to the nails above and below the break which gave me 8:1 or 9:1 scarf ratio. It was still a bit fiddly to get the new sections shaped to fit well but I managed.
Dry fitted and drilled undersized through the old holes in the plank I then glued them up with epoxy. Self tapping screws (thinner then my #10 copper nails) held it all together until the glue set. I then called in my dolly bird to hold one of my pieces of lead internal ballast against the nail while I riveted up. Each repair is therefore glued and secured by 6 riveted nails. 7 done, a few more to do.

Mariposa spent too long on a drying mooring before I got her. I suspect bouncing on her bilges twice a day for a couple of decades may have contributed to the problem.