Vessel Stability Overview • • • • • Watertight Integrity Vessel Subdivision Vessel Loading Intact Stability Damage Control Stability • The ability of a vessel to return to the upright position after being heeled by an external force. Heel Stability Concepts Heel Stability Concepts Heel Stability Concepts Heel Stability Concepts Heel Stability Concepts Heel Stability Concepts Heel Stability Concepts Why boats float • The weight of a boat equals the weight of water it displaces Stability Concepts Why boats float • The weight of a boat equals the weight of water it displaces Stability Concepts Why boats float • The weight of a boat equals the weight of water it displaces Stability Concepts Buoyancy Stability Concepts Buoyancy Stability Concepts Buoyancy Stability Concepts Buoyancy Stability Concepts Buoyancy Stability Concepts Buoyancy Stability Concepts Buoyancy Stability Concepts Buoyancy Stability Concepts Buoyancy Stability Concepts Buoyancy Stability Concepts Buoyancy Stability Concepts Buoyancy Stability Concepts Maintaining Watertight Integrity • Goal: To provide the vessel with a proven means to minimize the effects of flooding. Page 5 Maintaining Watertight Integrity Vessel Hull Downflooding Maintaining W/T Integrity - Vessel Hull Downflooding Maintaining W/T Integrity - Vessel Hull Downflooding Maintaining W/T Integrity - Vessel Hull Downflooding Maintaining W/T Integrity - Vessel Hull Downflooding Maintaining W/T Integrity - Vessel Hull Downflooding Maintaining W/T Integrity - Vessel Hull Downflooding Maintaining W/T Integrity - Vessel Hull Downflooding Maintaining W/T Integrity - Vessel Hull Downflooding Maintaining W/T Integrity - Vessel Hull Downflooding Maintaining W/T Integrity - Vessel Hull Downflooding Maintaining W/T Integrity - Vessel Hull Recommend Practices • Watertight condition of the deck, house and side shell must be maintained. • Discharge piping penetrating the hull should be fitted with check and positively closing valves • Inlet piping should be fitted with positive closing valves located at the shell plating. • Deckhouse openings should be fitted with weathertight doors. Maintaining W/T Integrity - Vessel Hull Page 6 Recommended Practices • Doors should be steel or equivalent material permanently attached to the bulkhead • Weathertight doors should open outward and be fitted with a minimum or two dogging devices in addition to hinges. • All emergency doors should be quick acting. • Propulsion machinery spaces above the bulkhead deck should be watertight. Maintaining W/T Integrity - Vessel Hull Page 6 Maintaining Watertight Integrity Vessel Subdivision Subdivision Watertight transverse bulkheads up to bulkhead deck down to the keel Maintaining W/T Integrity - Vessel Subdivision Page 5 Subdivision Maintaining W/T Integrity - Vessel Subdivision Subdivision Maintaining W/T Integrity - Vessel Subdivision Subdivision Maintaining W/T Integrity - Vessel Subdivision Subdivision Maintaining W/T Integrity - Vessel Subdivision Recommend Practices • Vessel should be subdivided with collision bulkhead and watertight bulkheads. • Collision bulkhead be stepless and intact up to the bulkhead deck. (No doors/scuttles) • Penetrations shall include valves operable from aft of the collision bulkhead and above the bulkhead deck. • All pipe penetrations shall be as far inboard and high as practicable • Minimize the number of pipe penetrations. Maintaining W/T Integrity - Vessel Subdivision Page 8 Recommend Practices • Ensure watertight bulkheads watertight. • Machinery spaces should be enclosed by W/T bulkheads (Engine room, auxiliary equipment). • W/T bulkheads with openings should be quick acting W/T doors and should always be kept closed. • Watertight doors should open outward from the machinery space. Maintaining W/T Integrity - Vessel Subdivision Page 5-6 Vessel Loading Freeing ports Deck Freeboard Draft Page 9 Vessel Loading Adding weight reduces freeboard and reduces reserve buoyancy Page 9 Recommended Practices • Keep weight low in the vessel. • Avoid adding weight above the main deck. • Secure gears and equipment to prevent loads from shifting. • Limit duration of side lifting operations. • Minimize number of partially filled tanks. • Do not overload. Vessel Loading Page 9 Stability Center of Buoyancy B Stability Definitions Page 10 Center of Buoyancy The point through which the force of buoyancy acts vertically upwards (B) B Stability Definitions Page 10 Center of Gravity Center of Gravity (G) is a downward force G B Stability Definitions Page 10 Center of Gravity (G) rises and falls when weights are moved, added, and/or removed. Fis h G B Stability Definitions Page 10 Center of Gravity G Fis B h Stability Definitions Page 10 Metacenter G B Stability Definitions Page 11 Metacenter Can be considered as being the pivot point when the vessel is being inclined. M G B Stability Definitions Page 11 Metacenter Stability Definitions Page 11 Metacenter Stability Definitions Page 11 Metacenter Stability Definitions Page 11 Metacenter Stability Definitions Page 11 Metacenter Stability Definitions Page 11 Metacenter Stability Definitions Page 11 Roll Period Shorter Roll Period Stable M G B The distance between G and M referred to as GM is the Metacentric Height This vessel has positive GM Stability Definitions Page 11 Roll Period Longer Roll Period Unstable G M B This vessel has negative GM Stability Definitions Page 11 Uncontrolled Weight Movements M G Stability Definitions Page 12 Uncontrolled Weight Movements M G Stability Definitions Page 12 Free Surface Effect G M Stability Definitions Page 13 Free Surface Effect G M Stability Definitions Page 13 Free Surface Effect M G Stability Definitions Unsecured Loads Live Tank M G B Unsecured Loads Recommended Practices • Limit free surface effect by minimizing the width of tanks and the number of partially filled tanks. • Secure all loads. Important Factors Affecting Vessel Stability M G B Page 14 Important Factors Affecting Vessel Stability M G B Load Height Page 14 Important Factors Affecting Vessel Stability Live Tank M G B Suspended Weight Page 15 Important Factors Affecting Vessel Stability Live Tank M G B Page 15 Important Factors Affecting Vessel Stability Vessel slips out from beneath weight Page 15 Important Factors Affecting Vessel Stability Live Tank M G B Restrain load to prevent vessel slip Page 15 THE END
