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Longitudinal bulkheads have a similar purpose, but damaged stability effects must be taken into account to eliminate excessive heeling. Today, most ships have means to equalize water in sections port and starboard (cross flooding), which helps limit structural stresses and changes to the ship's heel and/or trim.
Criteria for this dynamic stability effect remain to be developed. In contrast, a "tender" ship lags behind the motion of the waves and tends to roll at lesser amplitudes. A passenger ship will typically have a long rolling period for comfort, perhaps 12 seconds while a tanker or freighter might have a rolling period of 6 to 8 seconds.
Longitudinal stability for longitudinal inclinations, the stability depends upon the distance between the center of gravity and the longitudinal meta-center. In other words, the basis in which the ship maintains its center of gravity is its distance set equally apart from both the aft and forward section of the ship.
A pitch motion is an up-or-down movement of the bow and stern of the ship. The longitudinal/X axis, or roll axis, is an imaginary line running horizontally through the length of the ship, through its centre of mass, and parallel to the waterline. A roll motion is a side-to-side or port-starboard tilting motion of the superstructure around this ...
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).
The Code contains both mandatory regulations and recommended provisions, setting out the minimum stability standards for ships. [6] This includes information on precautions against capsizing, metacentric heights (GM), righting levers (GZ), rolling criteria, Free surface effect and watertight integrity.
The sheer is a measure of longitudinal main deck curvature in naval architecture. The sheer forward is usually twice that aft. Increases in the rise of the sheer forward and aft build volume into the hull, and in turn increase its buoyancy forward and aft, thereby keeping the ends from diving into an oncoming wave and slowing the ship.
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]