Then massive headache yesterday evening... that's what I wrote on Tigertiger post...
Basically, the instructions tell me to cut my wooden keel at 2 positions, in essence to free the fin slot which is supposed to lie between the cuts.
The first cut is measured at 11 1/2" away from the aft end of the keel.
I measured once, twice, thrice (how to say "4 times" and "5 times" in one word ?) but to no avail : the instructions are telling me to cut my keel inside my slot... instead of at its edge.
I reported on the keel the position of the slot (it's easy to see because my keel is not quite glued on the plastic at this place, remember the concavity of the hull ?) with this white piece of paper. And see my ruler : 11 1/2" is about 3/4" inside.