Which component represents the main centerline or backbone of a vessel?

The keel is the component that represents the main centerline or backbone of a vessel. It runs along the bottom of the boat and provides structural support, stability, and a means of directional control. The keel also helps to counteract the force of wind on the sails, making it essential for maintaining balance while sailing.

In addition to its structural role, the keel plays a significant role in the hydrodynamics of the vessel, helping to reduce sideways drift and improve overall performance in the water. Different types of keels can be found on various vessels, designed to suit specific purposes, such as racing or cruising.

The other components mentioned serve different functions: the displacement hull pertains to the shape of the boat that allows it to move through water effectively, the hull is the exterior structure that encompasses the entire watercraft, and the deck is the surface that people walk on. While all of these parts are essential to the overall functionality of a boat, none serve as the central backbone like the keel does.