Just sitting here thinking about stoneage boatbuilding. Take a dugout canoe, then another, then another. Place them side by side. Like this.
UUU
With me so far? The left hand peak is the port gunwhale, the right hand peak is the starboard gunwhale. Join them together ( with mortice and tenon joints) than get rid of the peaks inbetween. Now we have a flat bottom boat. OK maybe I am mad, but gosh it's fun.