Stability- SQA exam UPDATED ACTUAL Exam Questions and
CORRECT Answers
CW (coefficient of fineness of the water-plane area) - Is defined as the ratio of the ships water-
plane area to the area of a rectangle having the same length and breadth of the ship at the
waterline in question
CB (block coefficient) - The block coefficient (CB) of a ship is the ratio of the underwater
volume of a ship to the volume of the circumscribing block. Value must be less than 1.00.
Explain what is meant by Equilibrium - Equilibrium is the term used to describe a vessel that is
afloat. It is a word made up of two words namely equal, and balance. A vessel will float when the
forces of weight and buoyancy are equal, and they balance - that is both B and G are in the same
vertical line, and the vessel is not being acted on by an external force (a force other than
buoyancy or weight).
Freeboard - The vertical distance from the summer load line to the freeboard deck. The freeboard
deck is normally the uppermost complete deck exposed to weather and sea.
Water plane area(WPA) - The enclosed area of the hull at the waterline is the waterplane area.
The Water-plane area is used to determine the TPC of a ship.
Centre of gravity - Is the point through which the total weight force (wf) of the ship can be
considered to act vertically downwards. It's position will depend upon the distribution of the
weight of the vessel and everything on board.
Whenever weights are shifted, loaded or discharged G will move.
DRAW DIAGRAM
Centre of buoyancy - Is the geometric centre of the underwater volume of the ship. It is the point
through which the total force of buoyancy is considered to act vertically upwards. It's position
, will constantly move as the ship moves in a seaway. The position of B has nothing to do with the
disposition of weights within the ship.
DRAW DIAGRAM
Initial transverse metacentre - This is the point of intersection of the lines of action of buoyancy
force (Bf) when the ship is in the upright and subsequently heeled conditions within small angles
of heel(up to 10 degree).
DRAW DIAGRAM
Intial Metacentric height (GM) - Is the vertical distance between the ships centre of gravity and
the metacentre. the GM is very important in determining the initial stability of the ship.
DRAW DIAGRAM
Metacentre - The place where all the lines of buoyancy intersect
Stable condition - A ship is in a stable condition if, when heeled by an external force to a small
angle,it returns to the upright when the force is removed.
The ship has positive initial GM.
DRAW DIAGRAM
Unstable condition - A ship is in a unstable condition if, when heeled by an external force to a
small angle, it continues to heel further when the force is removed, GZ acts as a capsizing lever.
In this condition the ship has negative initial GM.
DRAW DIAGRAM
Neutral condition - A ship is in a neutral condition if, when heeled by an external force, it comes
to rest at an indeterminate(not exactly known) angle of heel within small angles. GZ remains at
zero within small angles of heel.
In this condition the ship has no GM , I.E G is in same pace as M.
DRAW DIAGRAM
CORRECT Answers
CW (coefficient of fineness of the water-plane area) - Is defined as the ratio of the ships water-
plane area to the area of a rectangle having the same length and breadth of the ship at the
waterline in question
CB (block coefficient) - The block coefficient (CB) of a ship is the ratio of the underwater
volume of a ship to the volume of the circumscribing block. Value must be less than 1.00.
Explain what is meant by Equilibrium - Equilibrium is the term used to describe a vessel that is
afloat. It is a word made up of two words namely equal, and balance. A vessel will float when the
forces of weight and buoyancy are equal, and they balance - that is both B and G are in the same
vertical line, and the vessel is not being acted on by an external force (a force other than
buoyancy or weight).
Freeboard - The vertical distance from the summer load line to the freeboard deck. The freeboard
deck is normally the uppermost complete deck exposed to weather and sea.
Water plane area(WPA) - The enclosed area of the hull at the waterline is the waterplane area.
The Water-plane area is used to determine the TPC of a ship.
Centre of gravity - Is the point through which the total weight force (wf) of the ship can be
considered to act vertically downwards. It's position will depend upon the distribution of the
weight of the vessel and everything on board.
Whenever weights are shifted, loaded or discharged G will move.
DRAW DIAGRAM
Centre of buoyancy - Is the geometric centre of the underwater volume of the ship. It is the point
through which the total force of buoyancy is considered to act vertically upwards. It's position
, will constantly move as the ship moves in a seaway. The position of B has nothing to do with the
disposition of weights within the ship.
DRAW DIAGRAM
Initial transverse metacentre - This is the point of intersection of the lines of action of buoyancy
force (Bf) when the ship is in the upright and subsequently heeled conditions within small angles
of heel(up to 10 degree).
DRAW DIAGRAM
Intial Metacentric height (GM) - Is the vertical distance between the ships centre of gravity and
the metacentre. the GM is very important in determining the initial stability of the ship.
DRAW DIAGRAM
Metacentre - The place where all the lines of buoyancy intersect
Stable condition - A ship is in a stable condition if, when heeled by an external force to a small
angle,it returns to the upright when the force is removed.
The ship has positive initial GM.
DRAW DIAGRAM
Unstable condition - A ship is in a unstable condition if, when heeled by an external force to a
small angle, it continues to heel further when the force is removed, GZ acts as a capsizing lever.
In this condition the ship has negative initial GM.
DRAW DIAGRAM
Neutral condition - A ship is in a neutral condition if, when heeled by an external force, it comes
to rest at an indeterminate(not exactly known) angle of heel within small angles. GZ remains at
zero within small angles of heel.
In this condition the ship has no GM , I.E G is in same pace as M.
DRAW DIAGRAM
