Hi

"The method proposed by the yardowner looks overkill to me and i cannot
understand where the benefits are (the economic benefits for the
yardowner seem obvious, he would do the job). Beside this it will
alter the way the planks expand (the strip will act as a wedge) so it
will just cause cracks somewhere else. "

Quite right but It will not harm the boat, it will be no problem case
the splines expand but if you didn't know ; a wooden boat don't need to
be caulked from the start fact is that real boatbuilding make it
without caulking --- some hammer a rod on the plank edges and plane
down flush, then when the wood are wet the volumes that is compressed
will expand more than the surronding wood, making a perfectly tight
seal , add a line of cotton and it stay that way very long . Caulking
btw. must be done with skills and care, done wrong it can harm more in
the described situation.
BTW caulking go in loops not filling up buttom up and there ought to be
a link to show, --- anyway a full set of caulking irons are round 14
different types among these a couple to caulk into the seam downverts
up by shaping the iron at an angle.
-------- A cake cutter, such steel wheel with a handle unsharpened are
the best choice if you realy want to "caulk" wiht that you use only
cotton.