Angle of loll is the state of a ship that isunstable when upright (i.e. has a negativemetacentric height) and therefore takes on an angle of heel to eitherport orstarboard.
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, themoment of inertia of the vessel'swaterplane (a plane intersecting the hull at the water's surface) increases, which increases the vessel's BM (distance from thecentre ofBuoyancy to theMetacenter). Since there is relatively little change in KB (distance from theKeel to the centre ofBuoyancy) of the vessel, the KM (distance fromKeel to theMetacentre) 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 GM of vessel equal to zero. When this occurs, the vessel goes to neutral equilibrium, and the angle of heel at which it happens is calledangle of loll.In other words, when an unstable vessel heels over towards a progressively increasing angle of heel, at a certain angle of heel, the centre of buoyancy (B) may fall vertically below the centre of gravity (G). Angle oflist should not be confused with angle of loll. Angle of list is caused by unequal loading on either side of centre line of vessel.
Although a vessel at angle of loll does display features of stable equilibrium, this is a dangerous situation and rapid remedial action is required to prevent the vessel from capsizing.[1][2][3][4]
It is often caused by the influence of a largefree surface or the loss of stability due to damaged compartments. It is different fromlist in that the vessel is not induced to heel to one side or the other by the distribution of weight, it is merely incapable of maintaining a zero heel attitude.