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Ship’s stability
1. UNIT I
SHIP’SSTABILITY
2. Slayt 2
Whenan object is afloat,
it is acted upon by two
forces; the downward
force of gravity and the
upward force of buoyancy
3. Slayt 3
Buoyancyis the ability
of an object to float.
4. Slayt 4
If an object is placed into waterand the weight of this object is
greater than the weight of an
equal volume of water, the
object will sink. It sinks
because the force of buoyancy
is less than the weight of the
object.
5. Slayt 5
However, if the weight of theobject is less than the
weight of an equal volume
of water, the object will float
6. Slayt 6
Centreof gravity is the point of
application of the gravitational
force on the ship.
7. Slayt 7
Centreof buoyancy is the
point of application of the
buoyancy force on a ship.
8. Slayt 8
9. Slayt 9
Whencargo is loaded to one
side of a ship, there will be a
temporary shift in the centre of
gravity. Once the ship tilts to
one side, the centre of
buoyancy will also shift.
10. Slayt 10
Theship's centre of gravity
determines the ship's stability.
11. Slayt 11
Stability may be defined asthe ability of a vessel to
return to her initial position
after inclination.
12. GM
G-GRAVITYM-METACENTRE
13. Positive stability - M above G
MG
L
B'
14. Neutral stability - M and G in same position
GM
W
L
B'
15. Negative stability - M below G
GM
W
L
B"
16. State that the following sentences true or false according to the text.
1-Twoforces act upon the
object when it is afloat.
17. Slayt 17
2-Thecentre of gravitational
force is centre of buoyancy.
18. Slayt 18
3-If ship inclines, the centreof buoyancy changes.
19. Slayt 19
4-If M is below G, this meansthat the ship is not stable.
20. SOME WORDS
Deflection (n) - Deviation,being deflected
21. Slayt 21
Equilibrium (n) - Balance22. Slayt 22
Incline (v) - To deviate from avertical position, to lean, to
slope
23. Slayt 23
Shift (v) - To change position ordirection
24. Slayt 24
Sink (v) - To fall down below thesurface of the water, to submerge
25. Slayt 25
Stable (adj.) - Steady, fixed26. Slayt 26
Tilt (v) - To incline, to slope27. B-Underline the true word or phrase in italics
1-Thegravitational force is
upward / downward force.
28. Slayt 28
2-Ifmetacentre is above / below
centre of gravity , this ship will be
stable.
29. Slayt 29
3-Whenthe force of buoyancy is
less than the weight of the object,
it sinks / floats.