the boat was built, the inner plank edges were touching, the outer edges
were angled away so you can put in caulking.

Plank edges do not normally touch there is a gap that will allow for the
ultimate swelling or expansion of the plank. If the caulking cotton is
driven to tight (or you fill the seam with glue or epoxy) the plank will
'pull it's fastenings". The expanding plank has to go someplace.


--
My opinion and experience. FWIW

Steve
s/v Good Intentions