| The expected outcome is that the student... |
Supports STCW elements... |
TOPIC - Introduction to stability
- defines and understands the following stability terms
- initial stability
- six motions of a vessel
- centers of gravity and buoyancy
- the couple
- transverse metacenter
- stable, neutral and unstable equilibrium
- metacentric height
- metacentric radius
- stiff, tender or crank condition
- defines the center of buoyancy (B) as being the center of
the under-water volume of the ship
- states that the force of buoyancy always acts vertically
upwards
- explains that the total force of buoyancy can be considered
as a single force acting through B
- explains that when the shape of the underwater volume of a
ship changes the position of B also changes
- states that the position of B will change when the draft
changes and when heeling occurs
- labels a diagram of a midship cross-section of an upright
ship to show the weight acting through G and the buoyancy force acting through B
- states that the buoyancy force is equal to the weight of the
ship
- labels a diagram of a midship cross-section of a ship heeled
to a small angle to show the weight acting through G and the buoyancy force acting
through B external force
- describes stability as the ability of the ship to return to
an upright position after being heeled by an external force
- defines the lever GZ as the horizontal distance between the
vertical forces acting through B and G
- states that the forces of weight and buoyancy form a couple
- states that the magnitude of the couple is displacement x
lever, Displacement x GZ
- explains how variations in displacement and GZ affect the
stability of the ship
- on a diagram of a heeled ship, shows:
- the forces at B and G
- the lever GZ
- states that the length of GZ will be different at different
angles of heel
- states that if the couple Displacement X GZ tends to turn
the ship towards the upright, the ship is stable
- shows that for small angles of heel (ø), GZ = GM x sin ø
- states that for a stable ship:
- Displacement x GZ is called the righting moment
- GZ is called the righting lever
- states that it is common practice to describe the stability
of a ship by its reaction to heeling to small angles (up to approximately 10°)
- states that the value of GM is a useful guide to the
stability of a ship
- describes the effect on a ship's behavior of:
- large GM (stiff ship)
- small GM (tender ship)
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21A6
21C2
21C2.1
21C6
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TOPIC - Center of gravity (KG)
- states that weight is the force of gravity on a mass and
always acts vertically downwards
- states that the total weight of a ship and all its contents
can be considered to act at a point called the center of gravity (G)
- states that the center of gravity (G) of a ship can move
only when masses are moved within, added to, or removed from the ship
- states that:
- G moves directly towards the center of gravity of added masses
- G moves directly away from the center of gravity of removed masses
- G moves parallel to the path of movement of masses already on board
- illustrates and demonstrates theory of moments to find KG
- performs calculations find the vertical of the center of
gravity resulting from adding, removing or moving masses
- calculates, by using moments about the keel, the position of
G after loading or discharging given masses at stated positions
- illustrates and demonstrates theory of moments to find shift
of G ( GG')
- calculates shift of G ( GG') using theory of moments
- states that if a load is lifted by using a ship's derrick
or crane, the weight is immediately transferred to the point of suspension
- states that if the point of suspension is moved
horizontally, the center of gravity of the ship also moves horizontally
- states that if the point of suspension is raised or
lowered, the center of gravity of the ship is raised or lowered
- calculates shift of G ( GG') with suspended weight using
theory of moments
- calculates the change in KG during a passage resulting
from:
- consumption of fuel and stores
- absorption of water by a deck cargo
- accretion of ice on decks and superstructures given the masses and their
positions
- defines and understands homogeneous and heterogeneous cargo
layouts
- understands the required accuracy for KG
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21B1
21B1.01
21C2
21C2.1
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TOPIC - Height of metacenter (KM)
- defines the transverse metacenter (M) as the point of
intersection of successive buoyancy force vectors as the angle of heel increases by
a small angle
- calculates center of buoyancy (KB)
- identifies and understands metacentric radius (BM)
- understands the importance of vessel breadth and initial
stability
- explains the relationship between TPI and area of the water
plane
- calculates metacentric radius (BM)
- states that, for small angles of heel, M can be considered
as a fixed point on the center line
- on a diagram of a ship heeled to a small angle, indicates G,
B, Z and M
- shows on a given diagram of a stable ship that M must be
above G and states that the metacentric height GM is taken as positive
- uses hydrostatic curves to find the height of the
metacenter above the keel (KM) at given drafts
- states that KM is only dependent on the draft of a given
ship
- inspects Stability Booklet for content
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21B1
21B1.01
21C2
21C2.1
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TOPIC - Metacentric height (GM)
- given the values of KG, uses the values of KM obtained from
hydrostatic curves to find the metacentric heights, GM
- states that the recommended initial GM differs with
different types of vessels
- defines natural and apparent rolling period
- understands the dangers inherent in synchronous and forced
rolling
- understands the relationship of GM and rolling period
- Describes the components of the empirical rolling period
formula
- calculates rolling period or value of GM by empirical
rolling period formula
- understands the effect of negative GM on a vessel
- describes the short form method of calculating initial
stability
- identifies minimum GM as a function of displacement or mean
draft using the Required GM Curve in the Stability Booklet
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21B1
21B1.01
21C2
21C2.1
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TOPIC - Inclining experiment
- describes the inclining experiment, including required gear
and data
- derives formulae to interpret inclining experiment
- shows on a diagram the forces which cause a ship to list
when G is to one side of the center line
- states that the listing moment is given by displacement x
transverse distance of G from the center line
- shows on a diagram that the angle of list (ø) is given by
tan ø = GG'/(GM x Displacement) where GG' is the transverse shift of G from the
center line
- states that in a listed condition the range of stability is
reduced
- given the displacement, KM and KG of a ship, calculates the
angle of list resulting from loading or discharging a given mass at a stated
position, or from moving a mass through a given transverse distance
- explains with reference to moments about the center line how
the list may be removed
- given the displacement, GM and the angle of list of a ship,
calculates the mass to load or discharge at a given position to bring the ship
upright
- given the displacement, GM and angle of list of a ship,
calculates the mass to move through a given transverse distance to bring the ship
upright
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21B1.01
21C2
21C2.1
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TOPIC - Dynamic stability
- states that righting arm alone can be used as an indication
of stability
- states that if initial stability, GM, of a vessel is
improved, stability at any angle of inclination will also improve
- states that for any one draft the lengths of GZ at various
angles of heel can be drawn as a graph
- identifies cross curves of stability and a curve of statical
stability
- states that different curves are obtained for different
displacements with the same initial KG
- draws statical stability curve from cross curves of
stability
- calculates correction for a vertical shift of G using the
formula, GG' sin ø = change in GZ
- calculates correction for a transverse shift of G using the
formula, GG' cos ø = change in GZ
- states that angles of heel beyond approximately 40° are not
normally of practical interest because of the probability of water entering the ship
at larger angles
- analyzes a given curve of statical stability, to obtains:
- initial slope of curve
- angle of inclination for the maximum righting arm
- importance of freeboard
- angle of maximum list
- dangerous angles of list and roll
- the angle of vanishing stability
- the range of stability
- explains the causes, describes how to recognize and
identifies the corrective measures for list caused by negative GM
- explains the causes, describes how to recognize and
identifies the corrective measures for lists caused by G being off the centerline
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21B1
21C2
21C2.1
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TOPIC - Free surface
- states that if a tank is full of liquid, its effect on the
position of the ship's center of gravity is the same as if the liquid were a solid
of the same mass
- shows by means of diagrams how the center of gravity of the
liquid in a partly filled tank moves during rolling
- states that when the surface of a liquid is free to move,
there is a virtual increase in KG, resulting in a corresponding decrease in GM
- states that the increase in KG is affected mainly by the
breadth of the free surface and is not dependent upon the mass of liquid in the tank
- states that tanks are often constructed with a longitudinal
subdivision to reduce the breadth of free surface
- states that free surface effects are increased or decreased
depending upon the relationship between the specific gravity of the liquid in the
tank and the liquid the vessel is floating in
- calculates specific gravity correction (r)
- describes the impact of:
- the displacement on free surface effects
- the beam of slack tank on free surface effects
- calculates free surface corrections
- uses free surface constants in stability booklet long forms
- understands the application of free surface corrections to
initial stability
- understands the proper position of cross-connection valves
for deep tanks relative to damage stability as a function of tank vertical position
and percentage full
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21A4
21B1
21C2
21C2.1
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TOPIC - Trim
- defines the following elements of longitudinal stability
- trim
- longitudinal center of gravity (LCG)
- longitudinal center of buoyancy (LCB)
- longitudinal center of flotation (LCF)
- parallel sinkage
- change of trim
- moment to trim one inch (MT1)
- states that trim may be changed by moving masses already on
board forward or aft, or by adding or removing masses at a position forward of or
abaft the center of flotation
- defines "center of flotation" as the point about which the
ship trims, and states that it is sometimes called the tipping center
- states that the center of flotation is situated at the
center of area of the waterplane, which may be forward of or abaft amidships
- uses hydrostatic data to find the position of the center of
flotation for various drafts
- defines a trimming moment as mass added or removed x its
distance forward or aft of the center of flotation; or, for masses already on board,
as mass moved x the distance moved forward or aft
- defines the moment to change trim by 1 inch (MT1) as the
moment about the center of flotation necessary to change the trim of a ship by 1
inch
- uses hydrostatic curves or deadweight scale to find the MT1
for various drafts
- calculates the change in trim given the value of MT1,
weights moved and the distances moved forward or aft,
- calculates the change of trim given the value of MT1, the
position of the center of flotation, masses added or removed and their distances
forward of or abaft the center of flotation,
- calculates parallel sinkage to find the new drafts given
initial drafts, weight to be loaded or discharged, and TPI
- calculates new drafts given initial drafts, weight to be
loaded or discharged, TPI, and the position of the center of flotation
- uses a trimming table to determine changes in draft
resulting from loading, discharging or moving weights
- states that in cases where the change of mean draught is
large, calculation of change of trim by taking moments about the center of flotation
or by means of trimming tables should not be used
- calculates final drafts and trim for a planned loading by
LCG method of trim calculation
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21B1
21C2
21C2.1
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TOPIC - Angle of loll
- shows that if G is raised above M, the couple formed by the
weight and buoyancy force will turn the ship further from the upright
- states that in this condition, GM is said to be negative and
Displacement x GZ is called the upsetting moment or capsizing moment
- explains how B may move sufficiently to reduce the capsizing
moment to zero at some angle of heel
- states that the angle at which the ship becomes stable is
known as the angle of loll
- states that the ship will roll about the angle of loll
instead of the upright
- states that an unstable ship may loll to either side
- explains why the condition of loll is potentially dangerous
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21A4
21B1
21C2
21C2.1
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TOPIC - Damaged stability
- lists the types of damaged condition
- states that flooding should be contained by prompt closing
of watertight doors, valves and any other openings which could lead to flooding of
other compartments
- states that cross-flooding arrangements, where they exist,
should be put into operation immediately to limit the resulting list
- states that any action which could stop or reduce the
inflow of water should be taken
- understands the dangerous effect of free communication with
the sea
- understands the effects of flooding on transverse stability
- explains remedial measures to improve transverse stability
- describes the lost buoyancy method of calculating effect of
flooding on transverse stability
- describes the added weight method of calculating effect of
flooding on transverse stability
- understands when to use the lost buoyancy method and when
to use the added weight method
- understands when intact buoyancy is an asset and when it
is a liability
- defines grounding force and understands its effect on KG
- understands and can explain reserve buoyancy, floodable
length, permeability
- understands the need for:
- establishing flooding boundaries
- restoring reserve buoyancy
- restoring stability
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21A4
21A8
21B1
21C2
21C2.1
21C2.2
21C2.3
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