A fin keel is a type of keel used in sailing vessels, designed to improve stability and performance. It is characterized by a vertical, fin-like shape that extends downward from the hull, allowing the boat to resist sideways motion while sailing. This design helps to enhance the boat's ability to sail upwind and maintain balance in various sea conditions. Fin keels are often found on modern sailing yachts and are favored for their efficiency and reduced drag compared to traditional full keels. They can be combined with a rudder for better maneuverability, making them popular among competitive sailors and recreational boaters alike.