The current problem is how to work out bevels for both the ribs and the
strakes. Is there a formula for this? Ideally the more general the
solution the better e.g. would work for a scale model as well as the
full size.

Sorry, I misread the OP and thought it was plywood stitch-and-glue
construction. On these boats people tend to putty the seams and ignore
bevel. Some run a saw along the seam to get a closer fit.

Carvel hull boatbuilders took bevels off the lofting diagrams.
I think you could get them off the drawings from hull design programs.
There are some free ones you could try. Do a search on Blue Peter Designs
for one that I knwo of. Or go to ww.boat-links.com.