Your vessel heels to 8 degrees to port and remains there. You suspect angle of loll. Describe the cause of loll, how you confirm it, and the correct corrective action.

A. Loll is caused by negative GM — the centre of gravity is above the metacentre. The vessel heels to the angle at which the righting lever (GZ) becomes zero on one side. Confirmed by: vessel lolling to alternate sides (port/starboard) and remaining at the loll angle rather than heeling progressively to one side. Correct action: lower G by adding ballast to double-bottom tanks — NOT by flooding high tanks first, which can cause the vessel to roll violently through upright to the opposite loll angle. The double-bottom tank increases the free surface effect initially before raising KM — add the lowest available ballast carefully.

B. Loll is caused by excessive windage on one side. Correct action is to put the wind on the opposite beam to bring the vessel upright before adding ballast.

C. Loll is indistinguishable from a list. The correct action for both is to transfer ballast from the lower side to the higher side to bring the vessel upright.

D. Loll is caused by a permanent list to one side due to off-centre loading. Correct it by transferring liquid ballast to the opposite side.

A. GM (metacentric height) is the distance between the centre of gravity (G) and the metacentre (M). A positive GM (M above G) indicates stable equilibrium — the vessel will right itself when heeled. A very low GM risks loll, slow period of roll, and potential capsize. A very high GM (stiff ship) causes a rapid, violent rolling motion that can create excessive dynamic loads on cargo, structures, and crew — which can be as dangerous as low stability.

B. GM is always a positive value. A negative GM means the ship is overloaded and must discharge cargo immediately.

C. GM is the distance between the keel and the metacentre. A higher GM always means a safer, more stable vessel regardless of its magnitude.

D. GM only applies to loaded conditions. In ballast, stability is assessed using only the KG value.

A. Key GZ curve features: range of stability (angle at which GZ returns to zero); maximum GZ and angle of maximum GZ; area under the curve (dynamical stability). IMO IS Code 2008 criteria: area 0-30 degrees minimum 0.055 metre-radians; area 0-40 degrees (or to flooding angle if less than 40) minimum 0.090 metre-radians; area 30-40 degrees minimum 0.030 metre-radians; maximum GZ at least 0.200 metres at 30 degrees or greater; initial GM not less than 0.150 metres.

B. The minimum GM under all criteria is 0.5 metres. The GZ curve must reach a maximum of at least 0.5m at any angle between 20 and 60 degrees.

C. The only IMO requirement is that the angle of vanishing stability must exceed 60 degrees. Area under the curve and initial GM are national flag state requirements only.

D. The IMO IS Code applies to new vessels only. Older vessels built before 2010 comply with the 1966 Load Lines convention stability requirements only.