How does the inclusion of water ballast affect a ship's stability?

The inclusion of water ballast plays a critical role in enhancing a ship's stability by lowering the center of gravity and increasing the metacentric height. When water ballast is added, it is typically distributed in the lower parts of the ship, which serves to lower the overall center of gravity. A lower center of gravity directly contributes to increased stability because it makes the vessel less likely to tip or heel over in response to external forces.

Additionally, by lowering the center of gravity, the metacentric height—defined as the distance between the center of gravity and the metacenter (a point where the buoyant force is applied)—is increased. A greater metacentric height means that the vessel can recover more effectively from heeling, thus enhancing its overall stability in rough waters or adverse conditions.

This is why the correct choice highlights both the lowering of the center of gravity and the increase in metacentric height, demonstrating how water ballast serves to improve the stability of a ship.