On a vessel with a list of 3 degrees to port, the OOW proposes to pump ballast from the port wing tank to the starboard wing tank to bring the vessel upright. The examiner asks you to evaluate this proposal and calculate the approximate shift in G.

A. Transferring ballast eliminates free surface effect because liquid is being moved, not added. It is always the safest way to correct a list.

B. Moving ballast from port to starboard will increase the list — G shifts away from the side being pumped from, which is the wrong direction.

C. Moving ballast has no effect on the list — only adding or removing weight changes the list. Only fuel consumption or cargo discharge can correct a list.

D. Transferring ballast from port to starboard will raise KG through free surface effect while the tanks are neither empty nor full, and will shift G to starboard to reduce the list. The shift of G horizontally = (mass transferred x transverse distance moved) / displacement. This is a valid procedure for correcting a list if the cause is off-centre G, but the OOW must be aware of the temporary increase in free surface effect as both tanks become slack, which will temporarily reduce GM before the receiving tank approaches full.

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

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

C. 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.

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

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

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. 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.