The (in)famous butt blocks are visible towards the center of the boat. This feature seems to cause some builders much angst. One of the most popular questions on the bateau.com builders support list is, "Do I have to use butt blocks? Can't I use a (taped, scarphed, etc.) joint instead?"
The answer in this case is no. The butt blocks have a structural stiffening function in addition to holding the 2 halves of the boat together. Personally, I can't see the objection especially since the bottom block is covered by the seat.