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Effects of Weight and Stability Lesson topic 3.4

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Enabling objectives ¶Determine the trim and heel of the vessel and recommend actions to correct the condition ·Record damage control messages ·Select terms and abbreviations associated with stability and buoyancy

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Shipboard draft marks zRoman numerals, (calculation marks) yUsed for measuring draft of the vessel from keel to waterline yDetermines displacement yNumerals are 3 inches in vertical projected height yRead at bottom of mark for whole feet yRead at bottom of horizontal bar for 1/2 foot yBar is 1 inch wide

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Shipboard draft marks zArabic numerals, (navigational drafts) yUsed to indicate operating drafts yProjections, if any, below the keel yNumerals are 6 inches in vertical projected height yRead at bottom of mark for whole feet yRead at top of mark for 1/2 foot yUsed primarily by ship's navigator

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Shipboard draft marks NAVIGATIONAL CALCULATION

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Shipboard draft marks zLimiting draft mark yIf exceeded, ship's ability to survive damage or heavy weather is jeopardized yLocated near draft numerals or amidships yDecision to exceed mark rests with the CO of the ship zInternal draft indicators yInstalled in larger ships yDraft can be read using remote draft gauge in DC Central

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Clinometers zHermetically sealed glass tube containing liquid which is mounted on a calibrated board zInstalled at vital stations zMost accurate under static conditions (fixed angles of Heel or List) zFour types, (A, B, C, and E) zTypes A and B are used to determine trim zTypes C and E are used to determine heel or list

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Clinometer

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Definitions of Terms Associated with Ship's Stability zBuoyancy yTends to force the object back up out of the water yUpward force is equal to weight of water which the object displaces zReserve buoyancy yVolume of the watertight portion of the ship above the water line zDisplacement yThe weight of the volume of water displaced by the hull, Weight of the ship.

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Definitions of Terms Associated with Ship's Stability zStability yTendency to remain or return to an upright position zCenter of Buoyancy yUpward force acting in a vertical line through the center of the volume displaced zCenter of Gravity yForce of gravity (weight) of the ship's structure and contained load acts vertically downward

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Principles of stability zFloating body is acted on by two forces yGravity yBuoyancy zObjects exist in three states yStable yNeutral yUnstable

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Forces Acting on Ship's Stability zCenters of buoyancy & gravity must lie in the same vertical line zShip is disturbed from rest by yWave action yWind pressure yTurning forces yRecoil of gunfire yImpact of collision or enemy hits yShifting of weights onboard yAdditional/removal of off center weights

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Forces Acting on Ship's Stability z"Stable Ship" develops a tendency to right itself yCalled a "Righting Moment"

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Principles of Heel, Roll, List, and Trim zHeel: Athwartships (side to side) inclination yRoll: Alternate Heeling from side to side yList: Permanent angle of Heel yThe major cause of listing is off-center weight zTrim yDistribution of weight so that the ship sits well in the water forward and aft yDetermined by difference between forward and after draft

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Effects of Weight on Ship Stability zWeight additions, removals and shifts yThe addition or removal of weight will always change the draft readings, and may effect trim, list and overall stability zCauses of off center weight yFlooding in compartments off the centerline yPumping liquids across the ship yThe shifting of ammunition, cargo, or personnel, across the ship

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Effects of Weight on Ship Stability zCorrecting for off-center weight yShifting weights from the listed side to the high side yJettisoning topside weights yDrain loose water ySuppressing free surface yMore drastic measures, such as completely filling partially flooded spaces, require careful consideration and are usually a last resort

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Free Communication with the Sea Effect (off centerline) zOccurs when a compartment is partially flooded, zEffect is increased as the ship rolls zThe movement of the water as the ship rolls exerts a strong, dynamic force on the bulkheads zAs more water is taken in, draft increases. zResults in stability being greatly reduced

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Ship's Flooding Effects and Liquid Load DC Diagram plate 1 zFlooding effect diagram yFlooding effect portion of this plate is to show the effect of flooded compartments on the ships stability yCompartments on the flooding effect diagram are color coded xPink - Flooding of the compartment results in a decrease in stability xGreen - Flooding of the compartment improves stability, even though free surface exists

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zYellow - Flooding of the compartment improves stability when completely filled, but stability is impaired when free surface exists zWhite or Uncolored - Flooding of the compartment will have no appreciable effect on the stability of the ship Compartments on the flooding effect diagram are color coded as follows

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Ship's Flooding Effects and Liquid Load DC Diagram plate 1 zIn the Flooding Effect part of this plate, the three numbers in the compartment represent yCenter, compartment number(s) yLeft upper, capacity in tons, S.W yRight lower, moment Ft. tons

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Ship's Flooding Effects and Liquid Load DC Diagram plate 1 zLiquid load diagram yTanks and voids that are fitted to carry liquids yIn the Liquid loading part of this plate, the five numbers in the compartment represent xCenter, compartment number xLeft upper, capacity in tons, (filled with cargo) xLeft lower, change in draft aft, (when flooded) xRight upper, list/degrees xRight lower, change in draft fwd, (when flooded) yTanks are color coded to indicate use

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Watertight integrity zMaintained to keep the ship stable zFlooding in spaces could result in change to yBuoyancy yCenter of gravity yDisplacement zMaintain correct material conditions to avoid flooding & aid in fire/smoke containment

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Summary and Review zShipboard Draft Marks zDefinitions of terms associated with ship's stability zPrinciples of Stability zForces acting on ship's stability zPrinciples of Heel, Roll, List, and Trim zEffects of weight on Ship Stability zFree Communication with the Sea Effect

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Summary and Review zShip's Flooding Effects and Liquid Load Diagrams (Isometric Damage Control Diagram number One) zWatertight Integrity

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