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Ship stability is an area of naval architecture and ship design that deals with how a ship behaves at sea, both in still water and in waves, whether intact or damaged. Stability calculations focus on centers of gravity , centers of buoyancy , the metacenters of vessels, and on how these interact.
The metacentric height is an approximation for the vessel stability at a small angle (0-15 degrees) of heel. Beyond that range, the stability of the vessel is dominated by what is known as a righting moment. Depending on the geometry of the hull, naval architects must iteratively calculate the center of buoyancy at increasing angles of heel.
A heavily listing ship The angle of list is the degree to which a vessel heels (leans or tilts) to either port or starboard at equilibrium—with no external forces acting upon it. [ 1 ] If a listing ship goes beyond the point where a righting moment will keep it afloat, it will capsize and potentially sink.
Simpson's rules are used to calculate the volume of lifeboats, [6] and by surveyors to calculate the volume of sludge in a ship's oil tanks. For instance, in the latter, Simpson's 3rd rule is used to find the volume between two co-ordinates. To calculate the entire area / volume, Simpson's first rule is used. [7]
The stability conditions of watercraft are the various standard loading configurations to which a ship, boat, or offshore platform may be subjected. They are recognized by classification societies such as Det Norske Veritas , Lloyd's Register and American Bureau of Shipping (ABS).
Angle of loll is the state of a ship that is unstable when upright (i.e. has a negative metacentric height) and therefore takes on an angle of heel to either port or starboard. When a vessel has negative metacentric height (GM) i.e. , is in unstable equilibrium, any external force applied to the vessel will cause it to start heeling.
Initial stability or primary stability is the resistance of a boat to small changes in the difference between the vertical forces applied on its two sides. [1] The study of initial stability and secondary stability are part of naval architecture as applied to small watercraft (as distinct from the study of ship stability concerning large ships ).
The 2008 version of the Code details guidelines on Second Generation Intact Stability for ships, specifically criteria for dynamic stability and damage assessment. [7] The Code is split into two parts. Part A contains mandatory criteria. Part B contains additional guidelines and recommendations. [4]