For what its worth, I drilled a 1 inch diameter hole in the bilge of my second boat, a 38 foot North Sea fishing cutter
, built of Oak on oak framing. That worked fine. I also drilled a hole in the keel
of my HO28 which was a steel
boat. My current steel
boat has a threaded hole in the keel at the bottom of the bilge sump. For the Grampian
26s I owned, I never drilled a hole in the bilge but it would have made things easier. Both of them used to get water about 3-4 inches deep building up over the winter. Scooping up ice water is no fun. Mopping it up with a sponge is even less fun. Your fingers turn blue from the cold.
Id say that if you did drill the hole, and sealed the bore sides with epoxy, you should have no problems. How to reseal it is a good question. If you haul out
every winter, I'd be inclined to plug the hole with a Bolt, washer, washer nut arrangement with some sealer. That way you could remove it when ever you need the drain. 1/2 inch diameter works well.