Center of Gravity and Buoyancy

• Center of Gravity is the point in a body where the gravitational force may be taken to act
• Center of Buoyancy is the center of gravity for the volume of water which a hull displaces

When the hull is upright the center of gravity and center of buoyancy are on the same vertical line, and the hull is

• stable

For most hulls the center of buoyancy is below the center of gravity and the hull is said to be meta-stable.

When the hull tilts the center of gravity remains in the same position related to the hull (as long as the hull is not changed and/or the cargo is not moved). The center of buoyancy will move to fit the new center of gravity for the volume of water replaced by the hull. In the beginning the gravity force and the buoyancy force will create a

• righting torque

that tries to move the hull back to the upright position.

If the hull is tilted to much the center of buoyancy will move to a position where the buoyancy and gravitation force starts to create a moment that work in the same direction and the hull will

• capsize