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Impaired Stability

Impaired Stability. Objectives. Definitions Addition of Topside weight Loss of Reserve Buoyancy Flooding (Solid and Partial) Free Surface Effect Fuel consumption Running aground. Definitions. Roll: Back/forth motion transversely Pitch: Back/forth motion longitudinally

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Impaired Stability

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  1. Impaired Stability

  2. Objectives • Definitions • Addition of Topside weight • Loss of Reserve Buoyancy • Flooding (Solid and Partial) • Free Surface Effect • Fuel consumption • Running aground

  3. Definitions • Roll: Back/forth motion transversely • Pitch: Back/forth motion longitudinally • Yaw: Side to Side motion • List: Difference between Port and Stbd draft (ie: constant heel) • Trim: Difference between fwd/aft draft (ie: constant pitch) • Center of Flotation: Point about which ship trims

  4. Addition of Topside Weight • Some unauthorized/additional topside weight often occurs: • Icing, Ammunition, Cargo, etc. • Effects: • Reduction in reserve buoyancy • Upward shift in G • Reduction of GM (metacentric height) • Reduction of righting arms • Loss of freeboard from increased displacement • Decreased stability

  5. Loss of Reserve Buoyancy • Can occur due to: • Poor maintenance • Failure to close fittings properly • Improper ballasting • Enemy action (torpedo, missile, mine, etc.) • If hole occurs above waterline, still reduces reserve buoyancy because of ship motion • Must restore watertight integrity ASAP

  6. Three Categories of Flooding • With respect to boundaries: • Solid • Partial with boundaries intact • Partial in free communication with sea • With respect to height of ship: • Weight of flooding above G • Weight of flooding below G • With respect to ship’s centerline: • Symmetrical flooding • Off-center flooding

  7. Solid Flooding • Def’n: complete flooding of a compartment • Can occur only if compartment is vented • More likely to occur below waterline • Effects: • Increased draft (like added weight) • Decreased reserve buoyancy

  8. Partial Flooding (Boundaries Intact) • Partial flooding means surface of flooding water lies between deck and overhead • Boundaries of compartment remain watertight • Affects stability of ship by: • Effect of added weight (high or low, on or off center) • Free surface effect (breadth of surface)

  9. Free Surface Effect • Compartment partially-filled with liquid • Surface of liquid tends to remain level as ship rolls/heels “free surface” • “Loose water” in compartment (not tank) • Causes reduction in GM stability

  10. Free Surface Effect

  11. Free Surface Effect • Causes shift in G as ship moves righting arm shrinks • Effect reduced by: • Installation of longitudinal bulkheads • “Pocketing” • Filling compartment solid

  12. Partial Flooding (Free Communication with Sea) • Sea flows in and out as ship rolls • Most likely will occur when there is a large hole that extends above and below the waterline (or if compartment is vented) • Ship can assume a pronounced list as more water is taken on

  13. Partial Flooding (Free Communication with Sea) • Water level in compartment tends to settle at sea level • Ship’s stability SIGNIFICANTLY affected by: • Added weight of water • Free-surface effect • Free-communication effect

  14. Fuel Consumption • As fuel is consumed, a reduction in stability occurs due to removal of fuel from fuel tanks (tanks usually below G) • To ensure stability maintained, as storage tanks empty, they are filled with seawater • Seawater pumped into STORAGE tanks only (not SERVICE tanks)

  15. Running Aground • Running aground is BAD: • “Career limiting move” • Adversely affects stability • In general, don’t attempt to back off once grounded even more damage • Enough said

  16. Any Questions?

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