Lead keel corrosion
Lead does not usually corrode very much, surface pits if at all. Difficult to tell from your brief description but are you saying the 1/4" dia. hole goes clear through the lead keel? Is it adjacent to the keel bolt? A possible suspect could be shore power induced electrolysis. Check for electrical connection between keel and battery and/or charger etc. In any case the hole should be easy to fill with epoxy once cleaned out. There may have been an impurity or gas bubble in the casting at that location or the bolt itself could be corroding. Keel bolts usually made of stainless steel are cast into the lead keel and generally fairly long. Sometimes J hooked or sometimes welded to s/s flat stock or bar to prevent rotation. Another area to watch for is corrosion to the threads in the area under the nuts/washers in the keel sump especially if different grade s/s was used for nuts and bolts. If neccessary a new bolt could be installed by drilling down through the sump and tapping it with a long ext. thread tap. Have a professional boat repair yard advise you.
