What effect does adding weight above the center of gravity have on a vessel's stability?

Adding weight above the center of gravity adversely affects a vessel's stability primarily by lowering the metacentric height. The metacentric height is a crucial factor in determining the stability of a vessel; it is the distance between the center of gravity and the metacenter. When weight is added above the center of gravity, it raises the center of gravity itself, resulting in a lower metacentric height.

As the metacentric height decreases, the righting arm—the horizontal distance between the center of gravity and the center of buoyancy when the vessel is heeled—also diminishes. This results in a reduced ability of the vessel to return to an upright position after being disturbed by external forces such as waves or wind. Therefore, stability is compromised, increasing the risk of capsizing or excessive heel.

Understanding this principle is essential for ensuring safe design and operation of vessels, especially in conditions where stability is crucial for performance and safety. The other options do not accurately reflect the relationship between weight distribution and stability, as adding weight above the center of gravity is inherently destabilizing rather than stabilizing or neutral.