MMC Ship Construction & Stability 2 — Questions and Answers
Question 1: What is the purpose of a ship's bilge keel?
- To reduce rolling motion (Correct answer)
- To increase propeller efficiency
- To protect the hull from grounding
- To support the mast
Correct answer: To reduce rolling motion
Bilge keels are longitudinal fins welded along the turn of the bilge to dampen rolling motion and improve ship stability.
Question 2: The righting moment of a vessel is equal to:
- Displacement multiplied by GZ (Correct answer)
- GM multiplied by draft
- KG divided by KB
- Freeboard multiplied by beam
Correct answer: Displacement multiplied by GZ
Righting moment equals displacement (W) multiplied by the righting arm (GZ), representing the force tending to return the vessel upright.
Question 3: A ship's metacentric height (GM) is considered dangerously small when it is less than:
- 0.15 meters (Correct answer)
- 1.0 meter
- 0.50 meters
- 2.0 meters
Correct answer: 0.15 meters
A GM of less than 0.15 m is generally considered dangerously small and indicates the vessel is at risk of capsizing.
Question 4: Which structural member runs longitudinally along the centerline at the bottom of a ship's hull?
- Keel (Correct answer)
- Gunwale
- Beam
- Stanchion
Correct answer: Keel
The keel is the primary longitudinal structural member along the centerline of the hull bottom, acting as the ship's backbone.
Question 5: Free surface effect in a partially filled tank reduces a vessel's effective GM because:
- The liquid shifts when the vessel heels, raising the effective center of gravity (Correct answer)
- The weight of the liquid increases the draft
- Air pockets form and reduce buoyancy
- The tank walls flex outward under pressure
Correct answer: The liquid shifts when the vessel heels, raising the effective center of gravity
When a vessel heels, liquid in a partially filled tank shifts to the low side, effectively raising G and reducing GM, degrading stability.
Question 6: The term 'reserve buoyancy' refers to:
- The watertight volume of the hull above the waterline (Correct answer)
- The distance from the keel to the center of buoyancy
- The weight of water displaced at full load
- The height of the metacenter above the keel
Correct answer: The watertight volume of the hull above the waterline
Reserve buoyancy is the intact watertight volume above the waterline that provides additional buoyancy if the vessel takes on water.
Question 7: A transverse watertight bulkhead on a ship primarily provides:
- Subdivision to limit flooding after damage (Correct answer)
- Longitudinal strength to resist hogging
- Support for deck machinery loads
- A mounting surface for cargo securing fittings
Correct answer: Subdivision to limit flooding after damage
Transverse watertight bulkheads divide the ship into compartments, limiting the spread of flooding in the event of hull damage.
MMC Ship Construction & Stability 2
What is the purpose of a ship's bilge keel?