Transcript
Grunt Productions 2007
A Brief By Lance GrindleyA Brief By Lance Grindley
VESSEL STABILITYVESSEL STABILITY
Grunt Productions 2007
Grunt Productions 2007
Stability - the tendency of a vessel to rotate one way or the other (to right itselfright itself or overturn)
Initial Stability - the stability of a vessel in the range from 0° to 7°/10°0° to 7°/10°
Definitions
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Definitions
Overall Stability - a general measure of a vessel's ability to resist capsizingresist capsizing in a given condition of loading
Dynamic Stability - the work donework done in heeling a vessel to a given angle of heel
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Roll – side to side or port to starboard. (Rotate about longitudinal axis) Pitch – up down or bow to stern. (Rotate about transverse axis)Yaw – twisting (rotate about vertical axis)
Sway – “sliding” laterally or side to side
Heave – up down as in lifted by waves.
Surge – “sliding” longitudinally or front back
Six Motions Of A Ship
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Definitions
ROLL - The action of a vessel involving a recurrent motion (Longitudinal Axis).
HEEL - Semi-permanent angle of inclination, caused by external forces.
LIST - Permanent angle of inclination caused by a shift in the center of gravity, -GM, or both.
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Laws Of Buoyancy
• A floating object has the property of buoyancy• A floating body displaces a volume of water equal in weight to the weight of the body.
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DISPLACEMENT
00
G
Capital W =
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DISPLACEMENT
04
G
B
Capital W =
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DISPLACEMENT
09
G
B
Capital W =
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DISPLACEMENT
16
G
B
Capital W =
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DISPLACEMENT
20
G
B
Capital W =
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Laws Of Buoyancy
• A floating object has the property of buoyancy.
• A floating body displaces a volume of water equal in weight to the weight of the body.
• A body immersed (or floating) in water will be buoyed up by a force equal to the weight of the water displaced.
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DisplacementDisplacement
► The weight of the volume of water The weight of the volume of water that thethat the
ship's hull is displacingship's hull is displacing
► Units of weightUnits of weight
long ton = long ton = 2240 lbs2240 lbs short ton = short ton = 2000 lbs2000 lbs metric tonne = metric tonne = 2204.72 lbs2204.72 lbs
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A push or a pull. Tends to produce motion or a change in motion.
Units: TONS, POUNDS, ETC.
Force
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Force
Parallel forces may be combined into one force equal to the sum of all forces acting in the same direction and so located to produce the same effect.
5 T
5 T
5 T
15 T
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WEIGHT: Gravitational force. Direction toward center of earth
UNITS: TONNES, LONG TONS, POUNDS, etc
MOMENT: The tendency of a force to produce rotation about an axis
MOMENT = F x d
ad
F
UNITS: TONNE-M3, FT-POUNDS, etc
F is the force of your hand while d is the length of your “wrench” & Moment is the torque applied.
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VOLUME - Number of cubic units in an objectUNITS: Cubic Feet, Cubic Inches, Cubic Meters
V = L x B x D
2 m3 m
1 m
V = 3 m x 2 m x 1 m
V = 6 m3
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Salt water = 0.9756 m3/tFresh water = 1 m3/t
SPECIFIC VOLUME - Volume per unit weight
UNITS: CUBIC METRES PER TONNE
2 m3 m
1 m
V = 6 m3
wflooding = Volume Sp. Vol
wflooding = 6 m3
0.9756m3/tonne
wflooding = 6.15 tonnes
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Stability Reference Points
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Stability Reference Points
CL
M
G
B
K
etacenter
ravity
uoyancy
eel
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Stability Reference Points
CL
M
G
B
K
other
oose
eats
ids
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B
WATERLINERESERVE BUOYANCY
B1
B
The Center Of Buoyancy
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B
WATERLINERESERVE BUOYANCY
Reserve Buoyancy, Freeboard, Draft and Depth Of Hull
Remember Remember this color!!this color!!
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Center Of Buoyancy
B
WLWL
B
WL
B
WL
B
WL
B
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BBBBBBBB
B
RULE OF THUMB RULE OF THUMB = “B” FOLLOWS = “B” FOLLOWS
THE WATERLINE.THE WATERLINE.
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G
G1
KGo
KG1
GG1
KGo
KG1
The Center Of Gravity
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Center Of GravityCenter Of Gravity
► Point at which all weights could be Point at which all weights could be concentrated.concentrated.
► Center of gravity of a system of weights is Center of gravity of a system of weights is found by taking moments about an found by taking moments about an assumedassumed center of gravity, moments are summed and center of gravity, moments are summed and divided by the total weight of the system.divided by the total weight of the system.
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Movements In The Center Of Movements In The Center Of GravityGravity
► G MOVES G MOVES TOWARDSTOWARDS A WEIGHT A WEIGHT ADDITIONADDITION
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Movements In The Center Of Movements In The Center Of GravityGravity
► G MOVES G MOVES TOWARDSTOWARDS A WEIGHT A WEIGHT ADDITIONADDITION
► G MOVES G MOVES AWAYAWAY FROM A WEIGHT FROM A WEIGHT REMOVALREMOVAL
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GGGGGGG1
KG1
KGo
G
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Movements In The Center Of Movements In The Center Of GravityGravity
► G MOVES G MOVES TOWARDSTOWARDS A WEIGHT A WEIGHT ADDITIONADDITION
► G MOVES G MOVES AWAYAWAY FROM A WEIGHT FROM A WEIGHT REMOVALREMOVAL
► G MOVES IN THE G MOVES IN THE DIRECTIONDIRECTION OF A WEIGHT OF A WEIGHT SHIFTSHIFT
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G1
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The Metacenter
CL
B
B20B45
M
M20
M45
M70
B70
METACENTER
M
BB1 B2
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Metacenter
BBBBBBB
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Metacenter
B SHIFTS
M
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CL
B
M
0o-7/10o
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CL
B B20
M
M20
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CL
M
M20
M45
B
B20 B45
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CL
B
B20
B45
M
M20
M45
M70
B70
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CL
M20M45
M70
M90
B
B20
B45B70
B90
M
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Movements Of The Movements Of The MetacenterMetacenter
THE METACENTER WILL CHANGE POSITIONS THE METACENTER WILL CHANGE POSITIONS IN THE VERTICAL PLANE WHEN THE SHIP'S IN THE VERTICAL PLANE WHEN THE SHIP'S DISPLACEMENTDISPLACEMENT CHANGES CHANGES
OROR
► WHEN B MOVES UP M MOVES DOWN.WHEN B MOVES UP M MOVES DOWN.► WHEN B MOVES DOWN M MOVES UP.WHEN B MOVES DOWN M MOVES UP.
RULE OF THUMB = “M” MOVES OPPOSITE OF “B”RULE OF THUMB = “M” MOVES OPPOSITE OF “B”
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M
G
B
M
G
B
G
M
B
M1
B1
G
M
B
M1
B1
G
M
B
M1
B1
G
M
B
M1
B1
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CL
M
G
B
K
GM
KG
BM
KM
Linear Measurements In Stability
METACENTRIC HEIGHTMETACENTRIC HEIGHT
HEIGHT OF METACENTERHEIGHT OF METACENTER
METACENTRIC RADIUSMETACENTRIC RADIUS
HEIGHT OF GRAVITYHEIGHT OF GRAVITY
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The Stability TriangleThe Stability Triangle
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M
GZ
CL
K
B
G
M
The Stability Triangle
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CL
K
B
G
MM
CL
G
B
K
B1
CL
M
G
B
K
B1
CL
M
G
B
K
B1
CL
K
B
G
M
B1
Z
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M
G Z
Where:Where:opposite = GZopposite = GZhypotenuse = GMhypotenuse = GM
Sin q = GZ / GMSin q = GZ / GMGZ = GM x Sin qGZ = GM x Sin q
Growth of GZ with GMGrowth of GZ with GM
Sin Sin = opp / hyp = opp / hyp
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CL
K
B
G
M
G1
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G
M
Z
G1 Z1
AS METACENTRIC HEIGHT (GM) DECREASES,
RIGHTING ARM (GZ) ALSO DECREASES
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G
B
MINITIALSTABILITY
0 - 7°
CL
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M
ZG
B B1
CL
OVERALLSTABILITY
RM = GZ x Wf
FINAL DISPLACEMENT
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Conditions of StabilityConditions of Stability
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GB1
M
Z
G
B1
M
B
G
B1
M
B
The Three Conditions of Stability
POSITIVE
NEUTRAL
NEGATIVE
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CL
K
B
G
M
Positive Stability
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CL
K
B
G
M
B1
Z
Positive Stability
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CL
K
B
GM
Neutral Stability
WHAT COULD CAUSE NEUTRAL STABILITY ?
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CL
K
BB1
Neutral Stability
GM
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CL
K
B
GM
Negative Stability
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K
B
GM
B1
Negative Stability
WHAT HAPPENS WITH NEGATIVE STABILITY ?
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NEUTRAL STABILITY IS AS BAD AS NEGATIVE STABILITY, BECAUSE IF YOU GET TO NEUTRAL,
SOMETHING “OUTSIDE YOUR CONTROL” WILL PUSH YOU OVER THE EDGE!!
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Free Surface EffectFree Surface Effect
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Free Surface EffectFree Surface Effect
► Free Surface Effect can become a problem Free Surface Effect can become a problem in a partially flooded vessel.in a partially flooded vessel.
► The partially flooded vessel and the water The partially flooded vessel and the water in her, will respond to the craft's heave, , in her, will respond to the craft's heave, , pitch, roll, surge, sway or yaw, e.g as the pitch, roll, surge, sway or yaw, e.g as the vessel rolls to port the water inside will vessel rolls to port the water inside will move, so that much of it is now on the port move, so that much of it is now on the port side of the vessel, and this will move the side of the vessel, and this will move the craft's centre of gravity and center of craft's centre of gravity and center of moment towards port. This has the effect moment towards port. This has the effect of slowing the craft's return to vertical.of slowing the craft's return to vertical.
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Free Surface EffectFree Surface Effect
► The free surface effect then becomes The free surface effect then becomes worse if the vessel then rolls through the worse if the vessel then rolls through the vertical to starboard. It takes time for the vertical to starboard. It takes time for the liquid in the vessel to respond and move liquid in the vessel to respond and move to the starboard side. to the starboard side.
► After the craft rolls through the vertical After the craft rolls through the vertical towards right (starboard), most of the towards right (starboard), most of the liquid moving in the craft's tank then liquid moving in the craft's tank then slams into the right (starboard) side of the slams into the right (starboard) side of the tank.tank.
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Free Surface EffectFree Surface Effect
► This has the effect of causing the This has the effect of causing the vessel to heel further over, as the vessel to heel further over, as the water mass hits the sides of the water mass hits the sides of the vessel. In strong winds, and heavy vessel. In strong winds, and heavy sea, this can become a positive sea, this can become a positive feedback loop, causing each roll to feedback loop, causing each roll to become more and more extreme, become more and more extreme, until the vessel capsizes.until the vessel capsizes.
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Free Surface EffectFree Surface Effect
► The higher up this water movement The higher up this water movement occurs, especially above either the occurs, especially above either the craft's center of buoyancy or center craft's center of buoyancy or center of gravity, the more pronounced the of gravity, the more pronounced the instabilities.instabilities.
► If this vessel is being towed, it could If this vessel is being towed, it could capsize, and take the towing vessel capsize, and take the towing vessel with it.with it.
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Free Surface EffectFree Surface Effect
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Draft Marks and Plimsoll LinesDraft Marks and Plimsoll Lines
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How to read draft marks…How to read draft marks…
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Plimsoll MarkPlimsoll Mark
The Plimsoll Mark diagrammed above is for the starboard side of a vessel; on the port side, the markings are reversed. The center of the disk is placed at the middle of the loadline. The lines are one inch think.
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Plimsoll MarkPlimsoll Mark
The letters signify:
LTF Lumber, Tropical, Fresh
LF Lumber, Fresh
LT Lumber, Tropical
LS Lumber, Summer
LW Lumber, Winter
LWNA Lumber, Winter, North Atlantic
LR Lloyds Register of Shipping
TF Tropical Fresh Water Mark
F Fresh Water Mark
T Tropical Load Line
S Summer Load Line
W Winter Load Line
WNA Winter Load Line, North Atlantic
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Thumb RulesThumb Rules
► B follows the WaterlineB follows the Waterline► M moves opposite of BM moves opposite of B► G movesG moves
Towards additionTowards addition Away from removalAway from removal Direction of shiftDirection of shift
► ““G moves faster than M”G moves faster than M”► ““G is G is nearnear the waterline” the waterline”
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These Guys Got it WrongThese Guys Got it Wrong
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