CMI Vessel Stability & Structural Integrity

Question 1

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

Accepted Answer

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

Answer

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.

Question 2

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

Accepted Answer

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

Answer

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.

Question 3

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

Accepted Answer

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

Answer

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.

Question 4

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?

Accepted Answer

0.090 m·rad

Answer

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.

Question 5

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

Accepted Answer

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

Answer

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.

(CMI) Certified Marine Investigator Practice Test

(CMI) Certified Marine Investigator Practice Test

CMI Vessel Stability & Structural Integrity