Righting moment and Righting Lever

  When a ship is inclined at an angle, the center of gravity remains the same. But the center of buoyancy changes over to a new position, creating a moment called righting moment.

Righting moment calculation
 Consider an instance: 
             Let the initial center of gravity of a ship be G and its center of
buoyancy be B. When inclined at an angle of θ Center of gravity remains same but center of buoyancy changes to "B1" .
                             

Therefore  these downward force due to center of gravity and upward force due to buoyancy force create a momentum of ΔgxGZ is called righting momentum.
         ( Mass of ship is             = Δ
           Weight of the ship is     =Δg
           The same force acting upward as buoyancy force
           Therefore momentum   = ΔgxGZ )

 The vertical separation between weight and buoyance force is  known as Righting Lever (GZ). Which varies with angle of heel