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www.sea-technology.com November 2016 / st 39 The use of flooding simulations is not just confined to catastrophic founderings involving major loss of life. Many accidents involve ingress of water resulting in large insurance claims without raising significant is- sues with regard to safety. Brookes Bell Safety at Sea regularly performs flooding simulations on flooded engine rooms arising from minor damages and operational/mainte- nance failures. In these cases, the company brings to bear collected expertise of ship operation and flooding simulations that is essential to understanding the reasons for the incident. In one flooding incident, the company was able to reproduce the breakup of an oil tanker that suffered a buckling collapse when subjected to high bending moments by simulating both halves of the vessel coupled at the col- lapsed section. Subsequent investigations and conclusions, which were validated by flooding simulation, identified the root cause of the incident; a result that would not have been possible without a plethora of experts and pioneering tech- nology. Addressing 'Black Spots' Brookes Bell Safety at Sea has worked on flooding simu- lations, ship survivability and forensic reviews of many tens of ship designs and real-life casualty cases. In numerous cases investigated by the team, vessels have suffered stabil- ity failure while operating in full compliance with all IMO and class society regulations. This raises bigger questions around the shipping indus- try's approach to safety, which has traditionally been dealt with by adhering to rules and regulations that dictate the design constraints for all new ships. However, this approach may on occasion be ineffective because vessel design tech- nology is developing faster than knowledge on ship opera- tion can be accrued. In practice, this means vessels designed to IMO and class standards may still possess "black spots", i.e., a small unidentified design problem that could lead to total loss of stability in worst-case scenarios. Historically within the shipping industry, such black spots would have been impossible to identify and confirm beyond reasonable doubt due to the inherent opinion-based nature of accident investigations. However, this outlook is changing, thanks to the combination of flooding simulations and conventional accident investigation expertise. Derbyshire In the 1980s and 1990s, a significant number of bulk carrier losses led to widespread concerns that the standards of design, construction and operation of these ships were inadequate. The most well-documented case was the loss of the Derbyshire in 1989, which disappeared without trace during a tropical storm. Its sinking remained a mystery for 20 years until the formal investigation into the cause of loss in 2000 confirmed that the failure of the forward hatch cov- ers had caused its demise. In the intervening years, a long and serious history emerged involving heavy weather damage to forepeak structures and closures, to forward hatch coamings and, above all, to forward hatch covers on bulk carriers. While hatch covers constitute the first-line of protection against flooding, they might be exposed to impact loads due to green seas in heavy weather. When taken onto deck by a ship pitching up, green water behaves like a water jet that causes the coaming and hatches to be- come awash with water. The nature of the loading on the coamings is very dynam- ic: short high-pressure impulses followed by hydrostatic loading. The hatch covers are first loaded horizontally (covers are pushed and displaced from their coam- ings, causing a loss of support) and then the "weight of the water" pushes them easily inward. In such conditions, the consequences of hatch cover failure in bulk carriers are potentially catastrophic. Hatch Cover Research The complex behavior of water on deck leading to dynamic loads on the hatch covers of bulk carriers means that predicting extreme hatchway loads due to green seas for bulk carriers in heavy weather is a serious engineering challenge. Notwithstanding this, in 2002, Luis Guarin, partner and naval architect at Brookes Bell Safety at Sea, sought to ad- dress the issue through his doctoral thesis, "A Probabilistic Risk Model of Green Seas Loads on Bulk Carriers". The re- search aimed to develop a probabilistic procedure for esti- mating the hatchways' loads due to green seas as a function of key design and operational parameters, with a view to offering recommendations for more rational standards for hatch cover design. Within this research model, testing and flooding simulations worked together, and the thesis's find- ings showed that structural resistance against green seas loads must be sufficiently high (in terms of risk). Also, the likelihood of damage due to green sea loads, or the level of such loads, should be reduced, either by innovation in design or by bringing to life again sound naval architecture design features such as forecastles and sheer. Addressing the Unknown The shipping industry is rightly pushing the boundaries of vessel design to achieve improved profitability, efficiency and environmental standards. While these benefits are nor- mally realized during vessel operation, progressive technol- ogy and innovations will continue to leave rare but signifi- cant accidents in their wake. As a result, there are certain circumstances where it is not known whether a vessel will be unable to recover from a stability issue until a crisis oc- curs. Flooding simulations, when used in combination with conventional accident investigation techniques, are already proving instrumental in identifying new black spots and support measures to address issues retrospectively in a cost- and time-effective manner. However, more time, resources and research are needed to assess uncertainties and accom- modate for them within vessel design and operation. This is a need Brookes Bell Safety at Sea has readily identified and continues to draw attention to within the wider ship- ping industry. ST Anthony York is a partner at Brookes Bell and a direc- tor at Safety at Sea Ltd., which merged with Brookes Bell in 2011. He has a B.E. in naval architecture from the University of Strathclyde and joined Safety at Sea Ltd. as a marine consultant when it was formed in 1999. He has considerable experience in the field of stability assessment and rule compliance and has worked on a number of casualty investigations, rang- ing from flooding simulations to stability calculations. "Flooding simulation technology helps marine accident investigators to identify the root cause of an accident by simulating the behavior of floodwater through a vessel."