AB Vessel Stability and Trim Flashcards
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Read the first 6 AB Vessel Stability and Trim flashcards as text
What does metacentric height (GM) measure?
Answer: A vessel's initial transverse stability
Metacentric height (GM) measures a vessel's initial transverse stability; a larger positive GM indicates the ship will resist rolling more strongly.
When is a vessel's GM considered 'positive'?
Answer: When the metacenter (M) is above the center of gravity (G)
A vessel has positive GM when M is above G, producing a righting moment that returns the vessel toward upright when heeled.
What is 'free surface effect'?
Answer: Loss of stability caused by liquid shifting in a partially filled tank
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.
What is a vessel's 'righting moment'?
Answer: The restoring force that returns a heeled vessel toward upright
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).
What happens to a vessel's initial stability when the center of gravity (G) rises?
Answer: Stability decreases as GM is reduced
As G rises, the distance between G and M (GM) decreases, reducing the vessel's initial stability and its resistance to rolling.
What does 'list' mean in vessel stability terms?
Answer: A permanent lean to one side caused by off-center weight distribution
List is a permanent transverse inclination caused by G being off the vessel's centerline due to unequal weight distribution.