I've only worked on two longitudinal strip built canoes, but both had the same problem: a lot of cupping of planking particularly along the bilge near the center of the canoe. Why? It's not easy to get rid of this cupping, but after soaking, steaming, and clamping, I can sometimes get another nail thru the center of the plank to hold it down permanently. So after dealing with this problem too often I had a thought - did any of the builders of longitudinal strip built, all wood canoes stagger the nails, for example, on one rib position the nails close to the lap in the usual way, and on the adjacent rib, put the nail thru the center of the plank? Seems this would be a good and permanent solution to the cupping problem. Tom McCloud