What is the geometric center of the underwater portion of a ship's hull called?

The geometric center of the underwater portion of a ship's hull is called the center of buoyancy. This term refers to the point at which the buoyant force, the upward force exerted by fluid against the weight of an object submerged in it, acts. Essentially, it is the centroid of the submerged volume of the hull. Understanding the center of buoyancy is crucial for ship stability; it influences how a ship behaves in water and how it reacts to tilting or rolling.

In contrast, the center of mass refers to the point where the mass of a body is concentrated and is crucial for determining the balance of the entire ship, but it is not specific to the underwater portion. The center of force is not a standard term used in naval architecture or physics, and the center of gravity, while it highlights the distribution of weight in a body, is not specifically focused on the submerged aspects of a hull. Therefore, the center of buoyancy is the most accurate term to describe the geometric center of the underwater part of a ship's hull.