> When a vessel has negative metacentric height (GM) i.e., is in unstable equilibrium, any external force applied to the vessel will cause it to start heeling.
> As it heels, the moment of inertia of the vessel's waterplane (a plane intersecting the hull at the water's surface) increases, which increases the vessel's BM (distance from the centre of Buoyancy to the Metacenter).
> Since there is relatively little change in KB (distance from the Keel to the centre of Buoyancy) of the vessel, the KM (distance from Keel to the Metacentre) of the vessel increases.
> At some angle of heel (say 10°), KM will increase sufficiently equal to KG (distance from the keel to the centre of gravity), thus making the GM of the vessel equal to zero. When this occurs, the vessel goes to neutral equilibrium, and the angle of heel at which it happens is called angle of loll.
> Normally at the angle of loll the vessel oscillates about its angle and returns to her angle of loll position
> However even though the vessel appears stable at this angle this condition is dangerous and must be corrected.
> An unstable ship with an angle of loll could capsize
Corrective Actions
> An angle of loll can be corrected only by lowering the centre of gravity, not by moving loads transversely.
> Press up all slack tanks and lower weight as possible
> If the ship is discharging cargo, discharge from the high side and which helps to lower the vessel center of gravity.
> Run up self-water in the ballast tank water on the low side.
> After this tank is full, run up its counterpart on the high side. Repeat these actions with other tanks until the ship becomes stable.