Rocks & mirror
Encyclopedia of Marine and Energy Technology

Angle of loll


The angle at which a ship with a negative initial metacentric height will lie at rest in still water. In a seaway, such a ship will oscillate between the angle of loll on SB and the one on PS. Depending upon external forces such as wind and waves a ship may suddenly flop over from PS to SB and then back again to PS. Such abrupt oscillation, different from a continuous roll, is characteristic for negative metacentric heights.

An angle of loll can be corrected only by lowering the centre of gravity, not by moving loads transversely. This can be done by moving weight downwards, adding water ballast in double bottom tanks or removing weight above the ship vertical centre of gravity.

Where empty ballast tanks are available these will afford the simplest means of lowering the ship’s centre of gravity. The correct procedure is to add ballast on the low side of the ship. The first effect will be to increase the angle of heel and to cause a loss of stability due to the free surface of the water, but this effect is soon cancelled and the angle of heel will rapidly decrease.