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 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

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

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

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

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

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)

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

Free Surface Effect

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

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

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

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)

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

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