Those two big holes you mention might be stern drains. I can't seem to recall every using them, so the rest of thisis just theory, yeah right! When I crewed on a Thistle, me captain put those in and covered them with spin repair tape. When you capsize and you get the mast point back up the boat is level with the water, and once you start getting forward motion, you punch out the tape and, they really drain the hull quickly, quicker than bailing. Without them the water becomes moving uncontollable ballast and when it decide to go forward it goes and that little bit of nose up attitude the boat had is now in dive mode. Ours were bigger in diameter than a beer, on one hand is good because the beer has a better chance of just going through than plugging up the hole. On the other hand . . .