Also be sure and take precautions to avoid core moisture intrusion into the transom, by carefully marking the holes, then overdriving them, route out about 1/4" of core beyond that hole, of the core, with Dremel or Allen key wrench... Paint the exposed core all around the hole with neat epoxy, the Fill this hole with high density filler/epoxy mixture, after set up, drill hole for the mini-jacker into this epoxy plug. This will avoid transom rot and core delamination down the line....(holds true for any hole in a cored part of the C Dory.)