A casualty can quickly become very complicated, and the steps needed to save the vessel are not always clear. The intact loading condition provided is unreliable. The tide is changing. The grounding location is unknown. The extent of damage and flooding is only partially known. Oil is leaking. The cargo is shifting. The vessel is moving, twisting and bending. Wind and waves are compounding the problem. Success in emergency response and salvage depends on quickly and correctly simulating the vessel’s condition, developing a plan to save the vessel, and effectively communicating the plan to others.
HECSALV™ (Herbert Engineering Corporation Salvage Software) was designed to make difficult situations like these more manageable. More than 30 years ago, engineers began developing this specialized software to analyze damaged vessels in afloat and grounded conditions using enhancements of the techniques they used to evaluate designs for intact and damage stability. Originally released in 1990, the software has evolved into a mature suite of programs that is considered the industry leading casualty response software for ships and offshore structures.
Time is Critical
The first hours after a casualty can be the most critical. Decisions made within the first 24 hours can greatly improve the vessel’s chance of survival and there is no time to struggle with complex software tools. First responders need software with easy to use visualization, calculation, and reporting tools so they can focus on stabilizing the situation. To do this a broad range of intact and damaged conditions must be easily simulated, both to represent the emergency as well as the “what-if” steps to stabilize the situation. This software had the added value of being completely compatible with Herbert-ABS’ on-board software (CargoMax™ for cargo carrying vessels, LMP for offshore vessels, and CruiseMax for passenger vessels); so loading conditions from these applications can be seamlessly evaluated by onshore support and emergency response engineers.
HECSALV™ has been used by ABS Consulting’s Rapid Response Damage Assessment (RRDA) program for the shipping and offshore industries since the service was established in 1990. When a troubled vessel that is enrolled in the program calls for help and the service is activated, the HECSALV model that was created when the vessel first subscribed becomes the foundation of the RRDA quick response. During a casualty, this model can help responders remain a step ahead of nature in resolving the incident. A vital part of salvage operations worldwide, HECSALV’s broad distribution throughout the industry makes it a common language of ship casualty.
Simulation with Fuzzy Data
Software tools can help responders manage the sometimes fuzzy or inaccurate information coming from the field. The intact loading condition is a good example. The first step in any simulation is to establish the condition of the vessel before the incident. The accuracy of the intact loading definition impacts the accuracy of the entire analysis. Tools are needed to quickly tune the analysis. By offering a flexible way to define the waterplane of the vessel from observed drafts and freeboard measurements HECSALV™ can quickly evaluate how well the intact condition matches drafts recorded before the incident and tune the following analyses to better simulate the situation. Similar tools can be used to tune any intact, damaged, or stranded condition.
If a responder is lucky then accurate loading condition information is available from the ship’s loading computer or other sources. This information can be manually input into the analysis.
When a ship is stranded something about the ground conditions might be known from natural charts or from reports on how the vessel stopped, but most often the actual shape of the seabed remains an unknown throughout the initial response. Because the details of the ocean floor topography are unknown, a best guess has to be made based on the information available. As long as the correct loading and damage conditions are received, HECSALV™ can use the observed drafts and calculate not only the ground reaction but also the position of the ground reaction along the ship bottom. Once the location is established, the vessel’s behavior through a changing tide can be simulated. Once a better picture of the underwater situation emerges the responder must have tools to accurately evaluate more complex grounding situations, such as a ship stranded on multiple pinnacles. It is a constant challenge for software designers to make all these tools easy to use in high-stress situations.
Damage can also be difficult assess because the extent of damage is not fully known, and for an older vessel the extent of corrosion can play a role. However, the residual longitudinal strength of a damaged vessel is critical and can set a boundary for a lightering plan or salvage operation. The Section Modulus Editor defines structural sections and the calculation of section properties including ‘’as built,” corroded and damaged structural elements. If sections are available at the time of the incident, a quick assessment of the impacts of damage and corrosion can be made for a simplified strength evaluation.
Once the fuzzy data is managed and there is confidence in the software simulation, the responder can get to work. If a ship starts to flood after a collision and cargo shifts causing the vessel to take on a dangerous heel, part of the response effort includes figuring out how to counterbalance the heel to prevent cargo from shifting further and to stabilize the vessel for towing. In the case of a grounding, responders need to figure out how much cargo or ballast must be removed and from which compartments so the ship can be refloated with sufficient stability. By modifying their computer model with data reports from the crew onboard the troubled vessel, emergency responders can develop a picture of the vessel that allows them to “try out” response strategies until a satisfactory approach is determined.
Developing and Communicating the Response Plan
Over time, more extensive planning that includes more detailed and more precise salvage steps has become necessary. Multitudinous factors need to be considered in an environment that is more and more demanding that oil outflow and marine pollution be controlled. The tools for carrying out these increasingly complex requirements must have increased capabilities without being overly complicated or subject to error. This software suite allows users to rapidly collect and process the available data, define the bounds of the problem and evaluate multiple scenarios for remedial actions. As more information comes in, the entire analysis can be updated from beginning assumptions to latter stage pump allocations, producing a refined and carefully considered salvage plan that can be clearly communicated to others.
The Macondo incident inspired further focus on emergency preparedness in the offshore industry. In response Herbert-ABS developed tools and reports specifically for offshore stability and salvage. New features include direct import of the last known loading conditions from LMP to expedite damage analysis and response, enhanced offshore modeling capabilities and 3-D graphics, a 6-degree of freedom calculator that accounts for non-vertical loads and forces from risers and moorings, an environmental force feature (wind, current and wave loads), and 360° stability surface calculations. A damage scenario generation tool is available to estimate possible damage. Given the last known pre-damage intact condition and observed damage drafts, it uses genetic algorithms to search for possible damage situations that closely match observed conditions.
Beyond Emergency Response
HECSALVV™ continues to evolve to meet the changing needs of the marine industry, and Herbert-ABS continues to push to make it a powerful but easy to use tool in high stress emergency response and salvage situations.
Features were recently added to model critical stability phases for FLO/FLO heavy lift (HL) operations. It deals with the critical stability phases of a FLO/FLO heavy lift operation, and the methods and practices to plan for and mitigate effects of reduced stability at these phases. To analyze a heavy lift, a full model must be developed for both the HL ship and the lifted ship. Each model includes all the data necessary to define and analyze the loading of both vessels and includes the full geometry of the hull and tanks defined using offsets, tankage details and strength limits, etc. Once modeled, there are two fundamentally different calculation methods available to analyze a heavy lift operation. These approaches include a rigid ship analysis and a flexible ship analysis. For both approaches, tools are provided to define the docking block plan from an existing docking plan or to develop a new docking plan for special situations such as a damaged vessel.
The rigid ship analysis treats both ships as rigid bodies and seeks a solution in the form of a classic static equilibrium, with the weight of the lifted ship applied to the HL, one through the blocks, which are internally represented as miscellaneous weights. The buoyancy of the HL ship is instead applied to the lifted vessel through the blocks, represented internally as pliable grounding pinnacles. The rigid ship approach can be used to evaluate the detailed stability and strength status of the heavy lift ship and the lifted ship at any step in the sequence so that both the “Draft at Instability” of the lifted ship and the “Minimum Stability” of the combined heavy lift ship can be determined. The rigid ship approach adopts an iterative methodology to find the equilibrium solution, where it first analyses the lifted ship assuming a set of dock block locations to get a ground reaction, then applying those loads to the HL ship, adjusting the dock block locations to reflect the new HL ship drafts and heel, computing a new set of reactions and then applying those to the HL ship, and so on. It converges when the reaction doesn’t change significantly. It handles only pure vertical forces.
The other method available to analyze heavy lift operations is the flexible ship analysis tool. This uses two beam finite element models connected by a set of rigid links and a set of unidirectional springs. The beams are located at the base of the HL ship and the height of the center of gravity of the lifted ship. This FE model can be viewed for any HL/Lifted ship configuration when the flexible ship analysis is run. This analysis approach can be used for more detailed analysis of block reactions and strength.