The bottom pic shows a piece of scrap offered up to the planed lower plank and stringers, to test for flatness and fit. This run of boards involves a lot more careful angling and planing as several curves interact on what has become a 'side' rather than a 'bottom' of the hull. I guess you'd call the bottom of this plank the turn of the bilge. In some places the stringer is tansformed into an almost triangular shape, while towards the stem it remains fairly square. You can see that the bulkhead will only touch the planking on one edge. The stringer has curved past it.
Before gluing this board the seat base for that side was finally cut to an accurate outline, using the final position of the plank as a guide for marking the protruding seat base ply. This can't really be done accurately until the stringers have their final shape.