Hi! I know from first hand experience that the skeg is not solid and is open into the keel on my 1976 M-17. Water leaking in my bottom gudgeon bolt made its way down via the transom (some sort of core was present in the '76) into the skeg and came to rest in the keel with out penetrating above the liner or showing itself in the boat. I recommend drilling right through the solid part of the hull instead. At least if that ever leaked, it would leak above the liner so you would notice it and hopefully it would stay out of your keel. My keel held more than 10 gallons of water before I finally made repairs and pumped it out. I'm hoping you're installing side scan sonar. best of luck! come to duluth! the summer is here! Martin p.s. I saw a white M-15 getting rescued by the coast guard last sunday. A crewman was apparently bailing through the port side locker as the boat was lashed to the side of an orange 30' RIB. I'm guessing that they were knocked down and their cockpit locker fell open.