What is the righting arm GZ?

• A. The horizontal distance between the line of action of buoyancy and the weight through G; determines stability.
• B. The vertical distance between deck and keel.
• C. The distance from center of gravity to the hull.
• D. The angle between true north and magnetic north.

Answer: (A)

The righting arm is the horizontal distance between the line of action of buoyancy and the weight acting through the center of gravity when the vessel heels. This separation creates a restoring moment: the weight (W) multiplied by GZ gives the righting moment that tends to bring the ship back upright. The larger the horizontal offset at a given heel angle, the stronger the restoring force, improving stability. If the offset were not horizontal or if buoyancy and weight aligned, there would be little or no restoring moment.

This concept contrasts with options that describe vertical distances (like deck to keel or center-of-gravity to hull) or irrelevant directions (like the angle between true and magnetic north).