Thanks, I ended up drilling in a bit farther, into the wood, with a smaller drill bit and unfortunately ended up with the drill going into the interior of the boat itself ( I looked over the transom, and there was the drill bit sticking out)!! I guess there was no need to drill through the plywood, after all. Interestingly, I'm at the absolute lowest point I can possibly drill, so if I drilled any lower, I would have come out the bottom of the boat. Fortunately, I drilled in with a small drill bit, and it will be an easy patch job.
I am wondering if the DSIIs had different hull designs in there derrieres.?? I've read on other posts that some have drilled in as far as 2 1/4 inches trying to install a drill plug, and others have mentioned being careful not to hit the self bailer. I just don't see this as a possibility on my boat.
The gap between glass and wood is about 1/2" and water does seem to be, albeit slowly, coming down that channel and out the hole I drilled, though still not sure if the bilge is draining fast enough (maybe that explains what I've read, and now see in your picture about some drains being moved starboard or port...) Interesting, too, that you hit nothing when sticking fingers/pencils in, as on mine, you'd hit wood in 1/2" (if I hadn't kept drilling....)
The mystery of the bilge drain continues....