Vessel Stability

 

A vessel is *inherently stable* if the center of gravity CG is below the center of buoyancy CB but if the CG is above the CB then the vessel is only stable if a tilt will move the CB in the direction of the tilt. Otherwise the vessel will tend to capsize. Wide vessels ensure the CB moves towards the side of the vessel that is sinking.

 

 

Water can serve as ballast and ballast can even be *lighter than water*. As long as it lowers the CG of the vessel, anything can act as ballast. Anything heavier than air can be ballast. This diagram shows an obvious case. You can see when the vessel heels, air is lowered and water is raised. That requires work to do and the tendency is to recover.