Ship Construction & Stability Flashcards

When a ship is said to be 'in irons' with respect to stability, this generally means:

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.

The angle of loll occurs when a vessel with negative GM:

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.

Hogging stress on a ship's hull occurs when:

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.

The load line mark on a vessel indicates:

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.

Which of the following actions will DECREASE a vessel's GM?

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.

The term 'deadrise' refers to:

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.

A damage stability calculation determines whether a vessel can:

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.