Murakami san uses this technique to a degree I’ve not seen anywhere else in Japan. He claims its enough, along with putting glue in the seams, to ensure that the boat will be watertight.
Some shots here as well of his use of the axe. It is his go-to tool for rouging out wood, but he cuts confidently to within 1/8th of an inch of his line. Here in the north the axe, normally called the ono in Japanese, is called the masakari.
And, I don't know if anyone is counting, but this is just Day Four and it sure looks like a boat!