After the floor of the canoe is done, it is time to add three thwarts for more sturdiness.  I use 1/8" x 1/8" cherry for these.  After I cut them to the desired length, I shape them with a piece of sandpaper glued to a cardboard roll, and taper each end of them until they are 1/16" thick.  They go in three places, one centered, and one on each end.  I use the third plank down from the top to locate them, and after applying a bit of glue, I wedge them in place.  I make sure they fit tightly, but not too much so.