MMC Ship Construction & Stability 3 — Questions and Answers
Question 1: When a ship is said to be 'in irons' with respect to stability, this generally means:
- The vessel has zero or negative metacentric height (Correct answer)
- The anchors are deployed simultaneously
- The propeller shaft is locked
- The helm is amidships with no rudder effect
Correct answer: The vessel has zero or negative metacentric height
'In irons' in stability context often refers to a condition of zero GM, where the vessel has no righting ability and is neutrally stable.
Question 2: The angle of loll occurs when a vessel with negative GM:
- Floats at an angle where GZ becomes zero (Correct answer)
- Sinks to a new waterline until buoyancy equals weight
- Achieves maximum righting arm
- Lists until the gunwale is awash
Correct answer: Floats at an angle where GZ becomes zero
Angle of loll is the equilibrium angle at which a vessel with negative initial GM finds a new GZ=0 position by heeling to one side.
Question 3: Hogging stress on a ship's hull occurs when:
- The midship section is supported while the bow and stern sag (Correct answer)
- The bow and stern are supported while the midship section sags
- The hull is twisted by asymmetric loading
- Excessive deck load causes the vessel to trim by the head
Correct answer: The midship section is supported while the bow and stern sag
Hogging occurs when buoyancy is concentrated amidships causing the ends to droop, putting the keel in compression and the deck in tension.
Question 4: The load line mark on a vessel indicates:
- The maximum allowable draft in specified conditions (Correct answer)
- The location of the center of buoyancy
- The height of the freeboard deck above the keel
- The position of the ship's bilge pumps
Correct answer: The maximum allowable draft in specified conditions
The Plimsoll load line marks the maximum safe loading depth for various ocean zones and seasons, ensuring adequate freeboard and stability.
Question 5: Which of the following actions will DECREASE a vessel's GM?
- Filling a double-bottom tank (Correct answer)
- Lowering heavy cargo from the deck to the hold
- Adding ballast water to the keel tanks
- Removing topside weight
Correct answer: Filling a double-bottom tank
Filling a double-bottom tank adds weight low in the ship but also creates a large free surface, which reduces effective GM via the free surface effect.
Question 6: The term 'deadrise' refers to:
- The rise of the bottom plating from the keel toward the bilge (Correct answer)
- The height of the stern above the waterline
- Vertical distance from keel to the lowest continuous deck
- The upward curvature of the weather deck
Correct answer: The rise of the bottom plating from the keel toward the bilge
Deadrise is the transverse rise or slope of the bottom plating from the keel outward toward the bilge, affecting hull form and stability characteristics.
Question 7: A damage stability calculation determines whether a vessel can:
- Survive flooding of specified compartments and remain afloat with adequate residual stability (Correct answer)
- Withstand hurricane-force winds without rolling excessively
- Operate with cargo shift in heavy weather
- Maintain propulsion after grounding damage
Correct answer: Survive flooding of specified compartments and remain afloat with adequate residual stability
Damage stability calculations verify that a vessel has sufficient residual buoyancy and righting energy after defined compartment flooding scenarios.
MMC Ship Construction & Stability 3
When a ship is said to be 'in irons' with respect to stability, this generally means: