Its a BULB on a KEEL. Trust me,I work in a boatyard, something I do and see everyday. It's used for balancing a sailboat, because the mast gives it a high center of gravity maing it easier to capsize. The bulb is extremly heavy and it lowers the center of gravity under the waterline to make the boat stable.
What you don't know is there's a life-sign and booze sensor hidden inside it, so that we boatbulders know when there's a lone woman and a lot of drink on board. We don't want to make a visit when the husband/boyfriend is on board
