When assessing a vessel's dynamical stability from a GZ (righting arm) curve, what does the area under the curve up to a given angle of heel represent, and why is this important when assessing the vessel's ability to survive a sudden gust or rolling motion?

A. The area under the GZ curve up to a given angle represents the dynamical (potential) energy the vessel can absorb before reaching that angle — comparing this area to the energy imparted by a sudden heeling moment (e.g. a gust of wind, or rolling in a beam sea) indicates whether the vessel has sufficient reserve to right herself without capsizing, which is more informative than the maximum GZ value or angle of vanishing stability alone

B. A larger area under the curve always indicates the vessel is overloaded

C. The area under the curve only matters for vessels carrying liquid cargo

D. The area under the GZ curve has no practical meaning and is only used for academic purposes

A. Only the Chief Engineer needs to consider this, never the deck watchkeeper

B. None — stability is fixed regardless of loading

C. Increased displacement generally raises the centre of gravity if weight is added high up, and free surface effects in partially-filled tanks can reduce the effective metacentric height (GM)

D. Additional weight always improves stability regardless of where it is placed

A. This only matters when the vessel is at anchor

B. Negligible — watertight doors below the waterline are rarely closed anyway

C. Only relevant if the vessel carries passengers

D. Significant — a failed watertight closure compromises the subdivision the vessel's damage stability calculations rely on, potentially allowing progressive flooding between compartments in the event of damage