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HANSA 10-2021

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SCHIFFSTECHNIK | SHIP TECHNOLOGY Hull stress monitoring enables innovation Analyzing and acting on hull stress and fatigue data can mitigate vessel or cargo loss, while providing a foundation for new, greener vessel and equipment designs Japanese Class NK released its Guidelines for Hull Monitoring in June, providing comprehensive requirements for improving the safety of the hull structure using advanced monitoring solutions. Subsequently, »Dream Clover«, a 211,000-dwt bulk carrier built by Japan Marine United Corporation for Daiwa Kisen was awarded the classification’s first Hull Monitoring notation, DSS(HM(F+LS,O)), in August. Class NK’s work on hull monitoring reflects a growing acceptance of hull monitoring technology, but regulators are still to mandate its use despite the huge potential for risk mitigation, so economic drivers continue as primary purchasing decisions. According to the Allianz Safety and Shipping Review 2021, »container losses at sea spiked last year [2020] and have continued at a high level in 2021, disrupting supply chains and posing a potential pollution and navigation risk. The number of container losses is the worst in seven years. More than 3,000 containers were lost at sea in 2020.« Measuring fatigue development Hull measurements are vital for naval architects The report explains that the rise in container losses may be driven by a combination of factors including larger ships and more stress loads due to extreme weather. If we take a conservative single container value of 50,000 $ the cost of avoidable hull damage in cargo terms alone can be significant. While real-time data is essential for Captains and Navigation Officers on board to operate according to the prevailing conditions and reduce the risk of structural damage, hull stress monitoring also adds value to incident investigation. In the case of loss, accident or human error, the data contributes to root-cause analysis as it is possible to indicate if i.e., cargo overloading, structural stress and fatigue were the catalyst for an incident. Further, hull monitoring data provides insight into structural fatigue over time, which is a vital KPI for long-term planning and asset lifecycle forecasting. A key application in this context is the verification of new ship designs by qualifying uncertainties that cannot be known until a vessel is operational. By measuring »fatigue development« in different seas and sea conditions, it’s possible over time to predict the effective vessel lifecycle. This is vital data for naval architects to apply in subsequent vessel designs and is also valuable for maintenance planning, as part of a condition-based monitoring system. Equipment and technology manufacturers can also leverage stress and fatigue data for new developments as exemplified by 38 HANSA – International Maritime Journal 10 | 2021

SCHIFFSTECHNIK | SHIP TECHNOLOGY new wind-assist technologies that use kites or sails to augment existing propulsion systems and reduce bunker costs while contributing to decarbonization. Classification society DNV has already developed the Notation WAPS (Wind Assisted Propulsion System) and has awarded an Approval in Principle (AIP) to Korea Shipbuilding and Offshore Engineering (KSOE) for a wing-sail auxiliary propulsion system for ships. Other solutions are at different stages of development, but a key enabler for all is the ability to measure hull stress data in real-time for safety and in the long-term for design verifications of new structural requirements. Growth in marine digitalization will make such data easier to access. Like many sensor technologies, hull monitoring data has generally been available in »silos«, but with integrated operational technology on board and cyber-secure, affordable cloud technology designed for maritime users available from multiple vendors, insight from hull stress measurement data can be achieved faster and in a more user-friendly, easily distributable fashion. Class NK’s guidelines and DSS notation are intrinsically linked to digitalization and technology integration. The analysis of stress monitoring measurements with data from diverse operational technology such as loading computers and Integrated Automation Systems in a single ‘digital space’ could lead to safety and ship design breakthroughs that may not be possible without such an integrated approach. Focus on Fiber Bragg Grating Class NK describes a hull stress monitoring system as »intended to collect information through sensors like a strain gauge or an accelerometer installed on the ship and perform condition monitoring and condition evaluation.« Fiber optic systems using the Fiber Bragg Grating (FBG principle) are perhaps the most costeffective and dependable way to acquire the data. Adapted and commercialized for maritime use as »SENSFIB Stress Monitoring Systems« by Light Structures, FBGs are an internal stripe pattern in the core of the optical fiber that strongly reflects one wavelength (or color) of light, enabling the measurement of current stress, fatigue accumulation, accelerations and slamming trends as well as sailing conditions in terms of sea state, wind, speed and position (with external sensors). Considering that traditional electro-mechanical measurement systems are more prone to failure in the maritime environment, FBG offer a more dependable data stream. FBG sensors are small and intrinsically safe, so they can be installed practically anywhere including vessels and hazardous zones covered by ATEX regulation. They are also immune to EMI for reliability and because FBG systems measure the wavelength of light, they provide the most accurate stress measurements possible. Importantly, no welding is needed for installation, which further lowers ownership costs and enables easier expansion to include i.e., fatigue monitoring in the water line and bow sensors for ice load monitoring etc. The integration of versatile and scalable sensor systems with operational systems and cloud-based data management platforms can allow stakeholders to generate more insight for realtime decision support systems. While this will avoid hull damage from stress and fatigue at sea, the same data is a valuable resource for developing safer and more efficient ships, marine operations and equipment for the future. Author: Karianne Pran Co-founder and Director of Engineering Light Structures © Light Structures HANSA – International Maritime Journal 10 | 2021 39

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