POSSE, the naval version of the HECSALV naval architecture software package from Herbert-ABS Software Solutions LLC, is being used by the UK MoD Salvage & Marine Operations Team for Heavy Lift to monitor these complex heavy lift operations and ensure the blocks arrive safely at the assembly yard. MoD and the U.S. Navy Supervisor of Salvage have supported the development of new POSSE tools for drydocking and heavy lift analysis for a number of years, and the new features have proven their value on these complex block movements around the UK.
Lower Block 04 (LB04), a large aft block weighing 11,200 tonnes and measuring 86m x 38m x 23m, was rolled onto a barge in Govan, Glasgow using 498 SPMT (Self Propelled Modular Transporter) axles. A detailed POSSE model that included both the barge and the roll-on loads was used to evaluate the heavy lift plan and to monitor the on board operation every step of the way. This lift was in a tidal zone, so the timing of ballast operations, roll-on, and the tide were critical. MoD needed a tool to evaluate the lift if the planned timing could not be maintained because of tide prediction errors, SPMT problems, pump failures, and other unforeseen issues. As axles of the SPMTs came aboard during a rising tide the team quickly evaluated the current state of the operation by entering the current ballast, roll-on position, and observed drafts into the POSSE system to make sure the operation was on schedule and working within a safe zone. The MoD team also used POSSE’s recent time sequence tool enhancements to quickly look ahead to make sure the operation would be safe until completion.
The barge with the block fastened securely was then towed to the float-off site near the Rosyth assembly yard. The barge had to ballast down, ground the stern for stability, and fully submerge its deck to a draft deep enough to float the large block off. Stability becomes very critical in these operations as the heavy lift barge’s main deck submerges and the barge loses waterplane area. POSSE was used once again by the MoD team to evaluate and monitor the operation. The float off procedure was analyzed using POSSE’s new 2-body heavy lift tools using a model that included detailed LB04 geometry, detailed barge geometry, and a simplified model of the support blocks and the ground. The pumping sequences to ground the barge were pre-modeled, and the on-site team was able to rapidly rerun the sequence during all stages of the operation to evaluate any last minute changes to the plan and react to unforeseen problems.
Herbert-ABS sets the standard for leading edge stability, load management and emergency response software solutions for the marine and offshore industries. A joint venture between Herbert Engineering Corporation and the American Bureau of Shipping, Herbert-ABS supplies marine and offshore software products that include LMP-Offshore (offshore load management), CargoMax (shipboard trim, stability and loading) and HECSALV (salvage engineering and design). Herbert-ABS is headquartered in San Francisco, with offices in Glasgow, Shanghai, Singapore and Busan.