Double-hull tankers, when loaded with oil cargo, contain that cargo within one or more cargo tanks which are separated from the tanker's side and bottom shell plating by double-hull compartments. These double-hull compartments are typically empty when cargo is being carried and are filled with water ballast during voyages when no cargo is on board. When cargo oil is being carried, the level of oil in the cargo tanks can extend as high as the underside of the vessel's upper deck, and the level of seawater outside the vessel's hull can extend as high as the vessel's allowed operating draft. When the vessel sustains bottom damage to its outer and inner hulls from grounding, and that damage extends vertically upward into a cargo tank, according to the laws of physics, the level of oil in the cargo tank will lower until it is in hydrostatic equilibrium with the level of seawater outside the ship. Until this point of equilibrium is reached, the oil will first fill any otherwise empty adjoining double-hull compartment to a level that is in hydrostatic equilibrium with the seawater outside the ship. Any oil remaining in the cargo tank above the equilibrium level of oil in the double hull compartment will escape outside the vessel and cause an oil spill. The amount of oil which will so escape is dependent on the distance between oil and seawater levels before damage occurred, the specific gravity of the oil cargo (typically 0.85-0.90 for most crude oils) compared to the specific gravity of seawater (typically 1.000-1.025), and the volume of the double hull compartment below the oil equilibrium level.
Although the apparatus and method of the present invention could be used in connection with many different designs of double-hulled tankers, it is believed to be particularly useful in conjunction with the double-hulled tanker constructions which are shown and described in the following documents:
______________________________________ U.S. Patents Patentee U.S. Pat. No. Issue Date ______________________________________ Tornay 4,638,754 January 27, 1987 Cuneo et al. 5,085,161 February 4, 1992 Goldbach et al. 5,090,351 February 25, 1992 Goldbach et al. 5,086,723 February 11, 1992 Goldbach et al. 5,269,246 December 14, 1993 ______________________________________ U.S. Patent Applications Inventor(s) Application No. Filing Date ______________________________________ Goldbach 07/953,141 September 29, 1992 Goldbach 08/033,357 March 18, 1993 Goldbach et al. 08/095,178 July 23, 1993 ______________________________________
(now, respectively, U.S. Pat. No. 5,320,055, issued Jun. 14, 1994, U.S. Pat. No. 5,293,830, issued Mar. 15, 1994, and U.S. Pat. No. 5,313,903, issued May 24, 1994).