Vessel Stability & Structural Integrity Flashcards

What does metacentric height (GM) measure in vessel stability analysis?

Answer: The distance between the center of gravity (G) and the metacenter (M)

GM is the vertical distance between the center of gravity (G) and the metacenter (M); a positive GM indicates the vessel will return upright after heeling, making it the primary measure of initial stability.

How does a vessel in a 'loll' condition differ from one with a 'list'?

Answer: Loll results from negative GM; list results from off-center weight or asymmetric loading

Loll arises when GM is negative (the vessel is unstable upright and seeks equilibrium at a heel angle), whereas list is caused by a transverse shift in the center of gravity from off-center weight distribution.

What does the GZ curve (righting lever curve) represent in a vessel's stability diagram?

Answer: The righting lever (arm) distance at various angles of heel

The GZ curve plots the righting lever—the horizontal distance between the lines of action of buoyancy and gravity—at successive angles of heel, providing a complete picture of the vessel's stability across its range of inclination.

Under the IMO Intact Stability Code (IS Code 2008), what is the minimum required area under the GZ curve from 0° to 40° for passenger vessels?

Answer: 0.090 m·rad

The IS Code (Part A, mandatory under SOLAS) requires the area under the GZ curve from 0° to 40° (or to the angle of flooding if less) to be not less than 0.090 m·rad, ensuring adequate dynamic stability reserves.

What is the 'free surface effect' in vessel stability?

Answer: The reduction in effective GM caused by transverse movement of liquid in partially filled (slack) tanks

Free surface effect reduces effective GM because liquid in partially filled tanks shifts transversely when the vessel heels, raising the virtual center of gravity and diminishing the righting moment.

When investigating a capsizing incident, what should a CMI investigator assess as the first priority?

Answer: Stability booklet and the actual loading condition at the time of the incident

The stability booklet and the reconstructed loading condition at the time of the incident are primary evidence for determining whether the vessel had adequate stability margins, which is the central question in any capsizing investigation.

The International Load Line Convention (Plimsoll marks) primarily regulates what aspect of vessel safety?

Answer: Minimum freeboard to ensure adequate buoyancy and stability reserves in different zones and seasons

Load line marks indicate the maximum allowable loading depths in various geographical zones and seasonal conditions, ensuring vessels maintain sufficient freeboard to preserve buoyancy and stability reserves against sea conditions.