Righting arm GZ
When the ship floating at rest in still water is inclined by an external force to a small angle fi, the centre of gravity G will remain in the same position but the centre of buoyancy moves towards the submerged side, to the new position Bfi. This create a moment WxGZ known as the righting moment. GZ is known as the righting arm.
The plot of the righting arm GZ calculated as the function of the heel angle, at constant displacement and vertical centre of gravity KG values, is used to measure the ship stability at large angles of heels. It is called the curve of statical stability.