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VESSEL STABILITY CANADIAN COAST GUARD AUXILIARY - PACIFIC Principles of Stability Definitions Definitions Stability - the tendency of a vessel to rotate one way or the other (to right itself or overturn) Initial Stability - the stability of a vessel in the range from 0° to 7°/10°

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## VESSEL STABILITY

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**VESSEL STABILITY**CANADIAN COAST GUARD AUXILIARY - PACIFIC**Definitions**Stability - the tendency of a vessel to rotate one way or the other (to right itself or overturn) Initial Stability - the stability of a vessel in the range from 0° to 7°/10°**Definitions**Overall Stability - a general measure of a vessel's ability to resist capsizing in a given condition of loading Dynamic Stability - the work done in heeling a vessel to a given angle of heel**Six Motions Of A Ship**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**Definitions**ROLL - The action of a vessel involving a recurrent motion (Longitudinal Axis). Semi-permanent angle of inclination, caused by external forces. HEEL - LIST - Permanent angle of inclination caused by a shift in the center of gravity, -GM, or both.**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.**G**00 DISPLACEMENT Capital W =**G**B 04 DISPLACEMENT Capital W =**G**B 09 DISPLACEMENT Capital W =**G**DISPLACEMENT B 16 Capital W =**G**DISPLACEMENT B 20 Capital W =**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.**Displacement**• The weight of the volume of water that the ship's hull is displacing • Units of weight long ton = 2240 lbs short ton = 2000 lbs metric tonne = 2204.72 lbs**Force**A push or a pull. Tends to produce motion or a change in motion. Units: TONS, POUNDS, ETC.**5 T**15 T 5 T 5 T 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.**WEIGHT:Gravitational force. Direction toward center of earth**UNITS: LONG TONS, POUNDS, etc MOMENT:The tendency of a force to produce rotation about an axis UNITS: FT-LT, FT-POUNDS, etc d F a MOMENT = F x d F is the force of your hand while d is the length of your “wrench” & Moment is the torque applied.**2 m**3 m 1 m VOLUME - Number of cubic units in an object UNITS: Cubic Feet, Cubic Inches, Cubic Metres V = L x B x D V = 3 m x 2 m x 1 m V = 6 m3**2 m**3 m V = 6 m3 1 m SPECIFIC VOLUME - Volume per unit weight UNITS: CUBIC METRES PER TONNE Salt water = 0.9756 m3/tFresh water = 1 m3/t wflooding = Volume Sp. Vol wflooding = 6 m3 0.9756m3/tonne wflooding = 6.15 tonnes**Stability Reference Points**M etacenter G ravity B uoyancy K eel CL**Stability Reference Points**M other G oose B eats K ids CL**B**The Center Of Buoyancy RESERVE BUOYANCY WATERLINE B B1**Reserve Buoyancy, Freeboard, Draft and Depth Of Hull**Remember this color!! RESERVE BUOYANCY WATERLINE B**WL**WL WL WL WL B B B B Center Of Buoyancy B**B**B B B B B B B B RULE OF THUMB = “B” FOLLOWS THE WATERLINE.**G1**G G1 G The Center Of Gravity KG1 KGo KGo KG1**Center Of Gravity**• Point at which all weights could be concentrated. • Center of gravity of a system of weights is found by taking moments about an assumed center of gravity, moments are summed and divided by the total weight of the system.**Movements In The Center Of Gravity**• G MOVES TOWARDS A WEIGHT ADDITION**Movements In The Center Of Gravity**• G MOVES TOWARDS A WEIGHT ADDITION • G MOVES AWAY FROM A WEIGHT REMOVAL**G1**G G G G G G G KG1 KGo**Movements In The Center Of Gravity**• G MOVES TOWARDS A WEIGHT ADDITION • G MOVES AWAY FROM A WEIGHT REMOVAL • G MOVES IN THE DIRECTION OF A WEIGHT SHIFT**B**B20 B45 METACENTER The Metacenter M B B2 B1 M20 M45 M M70 B70 CL**B**B B B B B B Metacenter**B SHIFTS**Metacenter M**0o-7/10o**M B CL**M20**M B B20 CL**M20**M45 M B B20 B45 CL**M20**M45 M M70 B B20 B70 CL B45**M20**M45 M70 B CL M M90 B20 B90 B45 B70**Movements Of The Metacenter**THE METACENTER WILL CHANGE POSITIONS IN THE VERTICAL PLANE WHEN THE SHIP'S DISPLACEMENT CHANGES OR • WHEN B MOVES UP M MOVES DOWN. • WHEN B MOVES DOWN M MOVES UP. RULE OF THUMB = “M” MOVES OPPOSITE OF “B”**M**M M M1 M M M1 M M1 M1 G G G G G G B B B1 B1 B1 B1 B B B B**Linear Measurements In Stability**M METACENTRIC HEIGHT GM METACENTRIC RADIUS BM G HEIGHT OF METACENTER KM B HEIGHT OF GRAVITY KG CL K**M**G B K The Stability Triangle M G Z CL**M**M M M M Z G G G G G B B B B B B1 B1 B1 B1 K K K K K CL CL CL CL CL

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