How does a ship’s center of gravity affect its stability?

In naval architecture, a ship’s centre of gravity (G) is a critical factor in determining its static stability and behavior at sea. Stability is primarily governed by the relationship between G and the metacentre (M), the point where the vertical line through the centre of buoyancy intersects the ship's centerline when the vessel is inclined.1234

• Stable Equilibrium: When the metacentre (M) is positioned above the centre of gravity (G), the ship possesses a positive metacentric height. In this state, if the ship tilts, the forces of weight and buoyancy create a righting moment that returns the vessel to an upright position.23
• Unstable Equilibrium: If the centre of gravity rises above the metacentre, the ship becomes unstable. In this condition, any tilt generates forces that increase the angle of heel, potentially leading to capsizing.23

The vertical position of G is dynamic and changes based on the distribution of cargo, fuel, and stores. Naval architects must carefully manage these weights to ensure G remains low enough to maintain adequate stability throughout a voyage.15