John,

I have been reading and planning to build a strip-built kayak someday
and I think part of the answer to your question is: The bead and cove
size has to be the same as the thickness of the wood strips.

That is to say, that you want a 1/4" bead and cove set for 1/4" thick
strips. Use a larger size if you will be using thicker planking.

Hope this helps,

Paul