SAMS Vessel Stability and Naval Architecture 2 — Questions and Answers
Question 1: The angle of loll occurs when:
- A vessel is overloaded and its draft exceeds the load line mark
- A vessel with negative initial GM finds a heeled equilibrium position (Correct answer)
- A vessel reaches its maximum righting lever on the GZ curve
- A vessel's trim exceeds safe operational limits
Correct answer: A vessel with negative initial GM finds a heeled equilibrium position
Angle of loll is the angle at which an initially unstable vessel (negative GM) heels until buoyancy geometry provides just enough righting moment to balance gravity, creating a heeled but momentarily stable position.
Question 2: Reserve buoyancy is best described as:
- The additional cargo capacity available above the assigned load line
- The intact watertight volume of the vessel above the waterline (Correct answer)
- The difference between light ship displacement and full load displacement
- The extra stability provided by permanently installed ballast
Correct answer: The intact watertight volume of the vessel above the waterline
Reserve buoyancy is the watertight volume above the current waterline that can provide additional flotation if the vessel takes on water or is overloaded, delaying or preventing sinking.
Question 3: The longitudinal center of gravity (LCG) is primarily used to calculate:
- The vessel's transverse rolling period in calm water
- The vessel's trim (fore-and-aft inclination) (Correct answer)
- The initial transverse metacentric height
- The righting arm at extreme angles of heel
Correct answer: The vessel's trim (fore-and-aft inclination)
LCG is compared to the longitudinal center of buoyancy (LCB) to determine whether the vessel trims by the head or stern; when LCG is forward of LCB the vessel trims by the head.
Question 4: The downflooding angle is the angle of heel at which:
- The vessel's propulsion efficiency drops below acceptable limits
- Water begins to enter the vessel through non-watertight openings above the waterline (Correct answer)
- The righting lever (GZ) reaches its maximum positive value
- The vessel's keel becomes visible above the water surface on the high side
Correct answer: Water begins to enter the vessel through non-watertight openings above the waterline
The downflooding angle is the heel angle at which seawater can enter through deck openings, ventilators, or other non-watertight closures, rapidly worsening stability and risking foundering.
Question 5: A GZ stability curve with a large area under it indicates:
- Poor initial stability and a tender vessel
- High freeboard requirements under load line regulations
- Good dynamic stability and strong resistance to capsizing (Correct answer)
- Excessive roll damping that causes structural fatigue
Correct answer: Good dynamic stability and strong resistance to capsizing
The area under the GZ curve represents dynamic stability—the energy needed to capsize the vessel—so a larger area means greater resistance to being capsized by waves, wind, or cargo shift.
Question 6: Deadweight tonnage (DWT) represents:
- The lightweight displacement of the vessel's hull and permanently fixed machinery
- The total weight a vessel can carry including cargo, fuel, ballast, crew, and stores (Correct answer)
- The vessel's full load displacement measured in long tons
- The weight of water displaced when the vessel floats at its assigned load line
Correct answer: The total weight a vessel can carry including cargo, fuel, ballast, crew, and stores
DWT is the difference between full load displacement and light ship displacement, representing everything a vessel can carry: cargo, fuel, fresh water, ballast, crew, passengers, and stores.
Question 7: Adding ballast weight at a low position in the vessel will:
- Raise the center of gravity and reduce transverse stability
- Lower the center of gravity and improve transverse stability (Correct answer)
- Have no effect on stability if the weight is on the centerline
- Increase freeboard and reserve buoyancy proportionally
Correct answer: Lower the center of gravity and improve transverse stability
Adding weight at a low position pulls the overall center of gravity (G) downward, increasing GM (since GM = KM − KG) and improving initial transverse stability.
SAMS Vessel Stability and Naval Architecture 2
The angle of loll occurs when: