I had great success using a Dremel type rotary tool as a grinder to remove only the very ends of the clinched tacks holding in each rib. Several advantages were apparent. 1) no chance of breaking or damaging planking. 2) importantly, the Dremel puts pressure in a very focused pea-sized spot, so sawdust and debris are minimal. 3) For the newbie canoe restorer or weekend craftsman there is almost no learning curve. 4) one doesn't use leverage or chisels or knives that, in the best of hands can slip and cause damage. 5) the rib comes out whole and can be used as a pattern.