Using the cut off tool shown in the prior picture, the rotten balsa was removed so that I could see where I should concentrate my next expansion of the opening. This also shows why the rotten core wasn't revealed when I surveyed the boat. The upper area of this wood is good in many places. The rot is patchy and does not reveal itself readily when using the "bonk with a hammer" test. The resin is drawn up into the kerfs in the balsa by capillary action, forming a resin lattice that helps masks a rotten core. Much of this area was only wet/rotten on the bottom.