Swing keel
A ballasted keel that pivots up into the hull, so a boat can be trailered and sailed in shallow water.
A swing keel is a heavy, ballasted plate that pivots on a pin and is raised with a winch or cable. Keel down it works like a shallow fin keel; keel up the boat draws only a foot or two and sits on a trailer. It is the defining feature of trailer-sailers such as the Catalina 22. The pivot pin, the cable, and the keel trunk are the parts that wear, and a keel that has been left down in a slip for years may have corroded or fouled. A centerboard differs in that it is unballasted and slides inside a stub keel that carries the ballast.