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Stability lrg
The document discusses vessel stability, including: - Initial stability refers to a vessel's stability from 0 to 7 degrees of heel. Overall stability is a general measure of a vessel's ability to resist capsizing. - The center of buoyancy (B) is the point where the total buoyancy force acts. It shifts upwards as a vessel heels. The center of gravity (G) is the point where all weights are concentrated. - The metacenter (M) is the intersection of the vertical line through B and the line of action of buoyancy as B shifts. As B moves up, M moves down. A higher metacenter means greater initial stability. - Positive stability exists when
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Stability lrg
- 1. Grunt Productions 2007 ABrief By Lance GrindleyA Brief By Lance Grindley VESSEL STABILITYVESSEL STABILITY
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- 3. 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
- 4. Grunt Productions 2007 Definitions OverallStability - 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
- 5. Grunt Productions 2007 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
- 6. Grunt Productions 2007 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.
- 7. Grunt Productions 2007 LawsOf 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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- 13. Grunt Productions 2007 LawsOf 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.
- 14. Grunt Productions 2007 DisplacementDisplacement ►The weight of the volume of water that theThe weight of the volume of water that 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
- 15. Grunt Productions 2007 Apush or a pull. Tends to produce motion or a change in motion. Units: TONS, POUNDS, ETC. Force
- 16. Grunt Productions 2007 Force Parallelforces 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
- 17. Grunt Productions 2007 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 a d 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.
- 18. Grunt Productions 2007 VOLUME- Number of cubic units in an object UNITS: Cubic Feet, Cubic Inches, Cubic Meters V = L x B x D 2 m 3 m 1 m V = 3 m x 2 m x 1 m V = 6 m3
- 19. Grunt Productions 2007 Saltwater = 0.9756 m3 /t Fresh water = 1 m3 /t SPECIFIC VOLUME - Volume per unit weight UNITS: CUBIC METRES PER TONNE 2 m 3 m 1 m V = 6 m3 wflooding = Volume Sp. Vol wflooding = 6 m3 0.9756m3 /tonne wflooding = 6.15 tonnes
- 20. Grunt Productions 2007 StabilityReference Points
- 21. Grunt Productions 2007 StabilityReference Points CL M G B K etacenter ravity uoyancy eel
- 22. Grunt Productions 2007 StabilityReference Points CL M G B K other oose eats ids
- 23. Grunt Productions 2007 B WATERLINE RESERVEBUOYANCY B1 B The Center Of Buoyancy
- 24. Grunt Productions 2007 B WATERLINE RESERVEBUOYANCY Reserve Buoyancy, Freeboard, Draft and Depth Of Hull RememberRemember this color!!this color!!
- 25. Grunt Productions 2007 CenterOf Buoyancy B WLWL B WL B WL B WL B
- 26. Grunt Productions 2007 B BB B BB B B B RULEOF THUMBRULE OF THUMB = “B” FOLLOWS= “B” FOLLOWS THE WATERLINE.THE WATERLINE.
- 27. Grunt Productions 2007 G G1 KGo KG1 G G1 KGo KG1 TheCenter Of Gravity
- 28. Grunt Productions 2007 CenterOf GravityCenter Of Gravity ► Point at which all weights could be concentrated.Point at which all weights could be concentrated. ► Center of gravity of a system of weights is found byCenter of gravity of a system of weights is found by taking moments about antaking moments about an assumedassumed center of gravity,center of gravity, moments are summed and divided by the total weightmoments are summed and divided by the total weight of the system.of the system.
- 29. Grunt Productions 2007 MovementsIn The Center OfMovements In The Center Of GravityGravity ► G MOVESG MOVES TOWARDSTOWARDS A WEIGHTA WEIGHT ADDITIONADDITION
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- 31. Grunt Productions 2007 MovementsIn The Center OfMovements In The Center Of GravityGravity ► G MOVESG MOVES TOWARDSTOWARDS A WEIGHTA WEIGHT ADDITIONADDITION ► G MOVESG MOVES AWAYAWAY FROM A WEIGHTFROM A WEIGHT REMOVALREMOVAL
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- 33. Grunt Productions 2007 MovementsIn The Center OfMovements In The Center Of GravityGravity ► G MOVESG MOVES TOWARDSTOWARDS A WEIGHTA WEIGHT ADDITIONADDITION ► G MOVESG MOVES AWAYAWAY FROM A WEIGHTFROM A WEIGHT REMOVALREMOVAL ► G MOVES IN THEG MOVES IN THE DIRECTIONDIRECTION OF A WEIGHTOF A WEIGHT SHIFTSHIFT
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- 35. Grunt Productions 2007 TheMetacenter CL B B20 B45 M M20 M45 M70 B70 METACENTER M B B1 B2
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- 39. Grunt Productions 2007 CL BB20 M M20
- 40. Grunt Productions 2007 C LM M20 M45 B B20 B45
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- 43. Grunt Productions 2007 MovementsOf The MetacenterMovements Of The Metacenter THE METACENTER WILL CHANGE POSITIONSTHE METACENTER WILL CHANGE POSITIONS IN THE VERTICAL PLANE WHEN THE SHIP'SIN THE VERTICAL PLANE WHEN THE SHIP'S DISPLACEMENTDISPLACEMENT CHANGESCHANGES 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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- 45. Grunt Productions 2007 CL M G B K GM KG BM KM LinearMeasurements In Stability ⇐⇐ METACENTRIC HEIGHTMETACENTRIC HEIGHT HEIGHT OF METACENTERHEIGHT OF METACENTER ⇒⇒ METACENTRIC RADIUSMETACENTRIC RADIUS ⇒⇒ ⇐⇐ HEIGHT OF GRAVITYHEIGHT OF GRAVITY
- 46. Grunt Productions 2007 TheStability TriangleThe Stability Triangle
- 47. Grunt Productions 2007 M G ZCL K B G M TheStability Triangle
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- 49. Grunt Productions 2007 M GZ Where:Where: opposite = GZopposite = GZ hypotenuse = GMhypotenuse = GM Sin q = GZ / GMSin q = GZ / GM GZ = GM x Sin qGZ = GM x Sin q Growth of GZ with GMGrowth of GZ with GM SinSin θθ = opp / hyp= opp / hyp
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- 51. Grunt Productions 2007 G M Z G1Z1 AS METACENTRIC HEIGHT (GM) DECREASES, RIGHTING ARM (GZ) ALSO DECREASES
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- 53. Grunt Productions 2007 M ZG BB1 CL OVERALL STABILITY RM = GZ x Wf FINAL DISPLACEMENT
- 54. Grunt Productions 2007 Conditionsof StabilityConditions of Stability
- 55. Grunt Productions 2007 G B1 M Z G B1 M B G B1 M B TheThree Conditions of Stability POSITIVE NEUTRAL NEGATIVE
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- 58. Grunt Productions 2007 CL K B GM NeutralStability WHAT COULD CAUSE NEUTRAL STABILITY ?
- 59. Grunt Productions 2007 CL K BB1 Neutral Stability GM
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- 61. Grunt Productions 2007 K B G M B1 NegativeStability WHAT HAPPENS WITH NEGATIVE STABILITY ?
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- 71. Grunt Productions 2007 NEUTRALSTABILITY IS AS BAD AS NEGATIVE STABILITY, BECAUSE IF YOU GET TO NEUTRAL, SOMETHING “OUTSIDE YOUR CONTROL” WILL PUSH YOU OVER THE EDGE!!
- 72. Grunt Productions 2007 FreeSurface EffectFree Surface Effect
- 73. Grunt Productions 2007 FreeSurface EffectFree Surface Effect ► Free Surface Effect can become aFree Surface Effect can become a problem in a partially flooded vessel.problem in a partially flooded vessel. ► The partially flooded vessel and the waterThe 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 thepitch, roll, surge, sway or yaw, e.g as the vessel rolls to port the water inside willvessel rolls to port the water inside will move, so that much of it is now on themove, so that much of it is now on the port side of the vessel, and this will moveport side of the vessel, and this will move the craft's centre of gravity and center ofthe craft's centre of gravity and center of moment towards port. This has the effectmoment towards port. This has the effect of slowing the craft's return to vertical.of slowing the craft's return to vertical.
- 74. Grunt Productions 2007 FreeSurface EffectFree Surface Effect ► The free surface effect then becomesThe free surface effect then becomes worse if the vessel then rolls through theworse if the vessel then rolls through the vertical to starboard. It takes time for thevertical to starboard. It takes time for the liquid in the vessel to respond and moveliquid in the vessel to respond and move to the starboard side.to the starboard side. ► After the craft rolls through the verticalAfter the craft rolls through the vertical towards right (starboard), most of thetowards right (starboard), most of the liquid moving in the craft's tank thenliquid moving in the craft's tank then slams into the right (starboard) side of theslams into the right (starboard) side of the tank.tank.
- 75. Grunt Productions 2007 FreeSurface EffectFree Surface Effect ► This has the effect of causing the vesselThis has the effect of causing the vessel to heel further over, as the water massto heel further over, as the water mass hits the sides of the vessel. In stronghits the sides of the vessel. In strong winds, and heavy sea, this can become awinds, and heavy sea, this can become a positive feedback loop, causing each rollpositive feedback loop, causing each roll to become more and more extreme, untilto become more and more extreme, until the vessel capsizes.the vessel capsizes.
- 76. Grunt Productions 2007 FreeSurface EffectFree Surface Effect ► The higher up this water movementThe higher up this water movement occurs, especially above either the craft'soccurs, especially above either the craft's center of buoyancy or center of gravity,center of buoyancy or center of gravity, the more pronounced the instabilities.the more pronounced the instabilities. ► If this vessel is being towed, it couldIf this vessel is being towed, it could capsize, and take the towing vessel withcapsize, and take the towing vessel with it.it.
- 77. Grunt Productions 2007 FreeSurface EffectFree Surface Effect
- 78. Grunt Productions 2007 DraftMarks and Plimsoll LinesDraft Marks and Plimsoll Lines
- 79. Grunt Productions 2007 Howto read draft marks…How to read draft marks…
- 80. Grunt Productions 2007 PlimsollMarkPlimsoll 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.
- 81. Grunt Productions 2007 PlimsollMarkPlimsoll 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
- 82. Grunt Productions 2007 ThumbRulesThumb 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 isG is nearnear the waterline”the waterline”
- 83. Grunt Productions 2007 TheseGuys Got it WrongThese Guys Got it Wrong
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Editor's Notes
- #25 Technically the reserve buoyancy of a ship is measured from the waterline to the DC deck. The minimum amount of reserve buoyancy required to meet a ship’s stability design criteria is from the limiting draft marks to the DC deck. RESERVE BUOYANCY IS OUR FRIEND!!!
- #63 VESSEL IN FORGROUND NORMALLY SAILS WITH 4-5 PEOPLE. VESSEL IN BACKGROUND NORMALLY SAILS WITH 7-8 PEOPLE. AS A “JOKE” THE VESSEL IN THE BACKGROUND “BOARDED” THE VESSEL IN THE FOREGROUND. I.E. LARGE TOPSIDE WEIGHT ADDITION. REMEMBER “G STARTS OFF NEAR THE WATERLINE.”
- #64 IMMEDIATELY START TO LIST DUE TO NEUTRAL GM… POSSIBLY SLIGHTLY NEGATIVE
- #65 THEY ARE AT THE NEUTRAL STABILITY POINT OR SLIGHTLY NEGATIVE GM POINT. NOTICE THAT THE MAIN SAIL IS NOT FILLED WITH WIND.
- #66 AS SOON AS THE SAIL FILLS…
- #67 OVER THEY GO. NOTICE INDIVIDUAL IN PINK (WHO WAS THE HIGHEST OF THE TOPSIDE WEIGHT ADDITIONS) WALKS DOWN THE MAST.
- #70 GETS TO THE KEEP AND …
- #71 STARTS HELPING PEOPLE IN THE WATER.
- #72 THEN THEY FILE THE INSURANCE CLAIM. MORAL OF THE STORY: NEUTRAL GM IS AS BAD AS NEGATIVE GM BECAUSE IF YOU GET TO THE NEUTRAL STABILITY POINT, SOMETHING OUT OF YOUR CONTROL LIKE WIND, WAVES, RUDDER FORCES ETC, WILL “PUSH” YOU OVER THE EDGE AND YOU WILL CAPSIZE. THE GOAL OF THE DCA IS TO KEEP WELL CLEAR OF THE NEUTRAL STABILITY POINT.