transom question

drilled some holes in the top. took a philips screwdriver with about a 4" shaft (all i could find) and pushed it in. buried to the hilt with no resistance. so i drilled a couple holes from inside the boat and at about 2" down hit wet, not rotten wood. 4" down, same thing. 6" down, solid wood. i dont understand how i can go from the top 4" and hit nothing but, go from the side and hit wood at 2". unless the wood is just rotted worse in the middle. i only drilled in about an inch or so from the side. didnt wanna tear things worse than they already are. this sucks guys. i dont need this right now. i been thinkin bout selling this boat to make some bills round here. now i cant even do that.