AB AB Vessel Stability and Trim

Question 1

What does metacentric height (GM) measure?

Accepted Answer

A vessel's initial transverse stability

Answer

Metacentric height (GM) measures a vessel's initial transverse stability; a larger positive GM indicates the ship will resist rolling more strongly.

Question 2

When is a vessel's GM considered 'positive'?

Accepted Answer

When the metacenter (M) is above the center of gravity (G)

Answer

A vessel has positive GM when M is above G, producing a righting moment that returns the vessel toward upright when heeled.

Question 3

What is 'free surface effect'?

Accepted Answer

Loss of stability caused by liquid shifting in a partially filled tank

Answer

Free surface effect is the reduction in effective stability caused by liquid in a partially filled tank shifting as the vessel heels, effectively raising G.

Question 4

What is a vessel's 'righting moment'?

Accepted Answer

The restoring force that returns a heeled vessel toward upright

Answer

The righting moment is the couple acting to restore a heeled vessel to upright, equal to the vessel's displacement multiplied by the righting arm (GZ).

Question 5

What happens to a vessel's initial stability when the center of gravity (G) rises?

Accepted Answer

Stability decreases as GM is reduced

Answer

As G rises, the distance between G and M (GM) decreases, reducing the vessel's initial stability and its resistance to rolling.

(AB) Able Seaman Exam Practice Test

(AB) Able Seaman Exam Practice Test

AB AB Vessel Stability and Trim