Both full-keel and fin-keel sail boats generally have fixed keels. On many smaller boats, however, the keel can be swung up into the hull from a pivot point at the top. This allow the boat to be positioned lower on a trailer or to maneuver in shallow water.
A swing keel is a weighted, narrow, fin-type keel that provides both ballast and lateral stability. A centerboard is similar but often is not weighted and thus provides only lateral stability.The advantage of both is the ability to reduce the boat’s draft for shallow water or trailering. The primary disadvantage is the maintenance of additional moving parts, such as the cable and winch used to lower and raise the keel or board. Swing keels are also generally lighter than fixed fin keels and thus provide less ballast.
Some larger cruising boats have a centerboard that can be lowered from within a fixed long keel, giving more lateral resistance when lowered for sailing close to the wind but a shallower draft and less drag when raised for sailing downwind or in shallower water.