Vessel Stability and Naval Architecture Flashcards
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What does metacentric height (GM) measure in vessel stability?
Answer: The vertical distance from the center of gravity to the metacenter
GM is the vertical distance from the center of gravity (G) to the metacenter (M) and is the primary indicator of a vessel's initial transverse stability.
A vessel with a negative GM will:
Answer: List permanently to one side and risk capsizing
A negative GM means G is above M, making the vessel unstable; it will heel to one side (angle of loll) and may capsize if the condition is not corrected.
The center of buoyancy (B) is located at:
Answer: The centroid of the underwater displaced volume of the vessel
The center of buoyancy is the centroid of the displaced water volume—the geometric center of the submerged portion of the hull—where the buoyant force acts upward.
Freeboard is defined as:
Answer: The vertical distance from the waterline to the upper deck edge
Freeboard is the vertical distance from the waterline to the freeboard deck edge, and its minimum value is regulated by international load line conventions to ensure reserve buoyancy.
The righting lever (GZ) in a stability analysis represents:
Answer: The horizontal distance between vertical lines through G and B when the vessel is heeled
GZ is the horizontal (perpendicular) distance between the vertical line through G and the vertical line through B at a given angle of heel, representing the righting arm per unit displacement.
Displacement tonnage of a vessel is equal to:
Answer: The weight of water displaced by the vessel, equal to the vessel's total weight
By Archimedes' principle, a floating vessel displaces a weight of water exactly equal to its own total weight, making displacement the most fundamental measure of a vessel's mass.
Bilge keels are fitted on a vessel primarily to:
Answer: Reduce rolling motion by creating hydrodynamic resistance as the vessel rolls
Bilge keels are longitudinal fins welded at the turn of the bilge that create hydrodynamic drag as the hull rolls, effectively damping and reducing the rolling motion.