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Technical Assistance and the US Navy's Program of Ship Salvage Engineering (POSSE)

SUPSALV salvage engineers provide technical and operational assistance to the U.S. Navy, as well as other federal agencies, such as the U.S. Coast Guard, Army Corps of Engineers, and Department of State. They have extensive training and expertise in naval architecture, salvage equipment, salvage operations and procedures, diving (qualified U.S. Navy divers), towing, and pollution abatement, and also have thorough knowledge of capabilities and practices of the commercial salvage industry. They are also fully equipped for "independent operations" and available for immediate mobilization for on-scene technical and operational assistance to the U.S. Navy and other Federal Agencies.

SUPSALV salvage engineers utilize POSSE to perform most required engineering analyses. POSSE is the most powerful salvage response software, providing capabilities to perform real-time engineering analyses of complex ship salvage situations, including assessments of ship stability, drafts/trim, intact or damaged structural strength, ground reaction and freeing force, oil outflow and flooding, lightering (weight removal) plan, tidal effects, etc. SUPSALV began development of POSSE in 1989 through a cost-sharing agreement with Herbert Engineering Corporation, and has continuously updated the program to improve capabilities and take advantage of advancing computer technology. As a benefit of the cost-sharing agreement, POSSE is fully compatible with the commercial salvage response software HECSALV and the commercial shipboard loading program CARGOMAX, and can also read data files of other commercial salvage response programs, including GHS.

POSSE performs rigorous numerical integration of hull and compartment offsets to calculate volumes. Forces (weight, buoyancy, reaction) are iterated to obtain equilibrium (afloat and aground). Effects of hull deflection can be included. Hull girder deflections can also be calculated based on hull girder inertias.

Notable new POSSE features include:

1. Non-rigid ground definition, including Multiple Point Grounding (MPG) analysis: Allows the salvage engineer to evaluate the effects of multiple contact points (up to and including complex drydock blocking analyses), a simple shelf, or a penetrable shelf.

2. Tide/Lightering Sequence (TLS): Allows the salvage engineer to calculate and display time-phased calculations of tide height, ballasting/deballasting/transfer of liquids from intact tanks, transfer of liquids and oil/water outflow/ flooding from damaged tanks, ground reaction, bending moments, shear forces, hull girder stresses, etc. A lightering plan, including transfer rates, start and stop times, and discharge amounts can be developed and printed for distribution to the salvage team.

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3. Hull axis rotation: Allows the salvage engineer to model capsized vessels and conduct detailed analyses for parbuckling/righting

4. Interfaces with the U.S. Navy's Ship Motion Program (SMP) and Ultimate Strength Program (ULSTR): Allows the salvage engineer to provide improved evaluations of dynamic wave bending moments and ultimate/residual strength characteristics of intact and damaged hull structure. SMP's results can also be used to provide detailed ship motions information (wave slap, accelerations, etc.).

5. Windows-based operation: Salvage response portions of POSSE have been converted to a 32-bit Windows application. Conversion of the modeling portion of POSSE should complete by the end of Fiscal Year 01. The key to successful utilization of POSSE is the experienced salvage engineer with solid working knowledge of naval architecture and salvage operations. Detailed ship naval architecture information must be combined with practical knowledge of the salvage operation in order to develop an effective and efficient salvage plan.

To provide basic overview and lessons learned of POSSE applications for actual salvage operations, SUPSALV provides POSSE Technotes to users of POSSE and other interested parties. Any POSSE user interested in authoring an edition of POSSE Technotes for a completed POSSE analysis should contact the POSSE Program Manager for guidelines.