What is meant by the term 'keel' in a boat?

The term 'keel' in a boat refers to the main centerline of a vessel. It is a crucial structural element running along the bottom of the hull from the bow to the stern. The keel provides stability and structural integrity to the boat, serving as a backbone that helps maintain the boat’s shape. In sailing vessels, the keel is also essential for underwater performance, as it helps counterbalance the forces acting on the hull, especially when the sail is filled with wind.

While other components of the boat, such as the hull and rudder, play important roles in stability and steering, the definition pinpointing the keel as the central structure that extends along the boat’s length is what makes this answer the most accurate. The other choices touch on aspects related to stability, steering, or hull structure but do not specifically define the keel as the central line of the vessel.