In order to cope with strengthened marine environmental regulations and to reduce fuel consumption, recently constructed vessels are equipped with an ultra-long stroke engine and apply engine de-rating technology. This was intended to improve propulsion efficiency by adopting a larger diameter propeller turning at a lower speed but also results in a significant increase in the torsional exciting force. Therefore, it is very difficult to control the torsional vibration of its shaft system by adopting a damper, for ships equipped with fuel-efficient ultra-long-stroke engines, even though previously, torsional vibration could be controlled adequately by applying tuning and turning wheels on the engine. In this paper, the vibration characteristics of an ultra-long-stroke engine using the de-rating technology are reviewed and dynamic characteristics of a viscous-spring damper used to control the torsional vibration of its shaft system are also examined. In case of ships have recently experienced an engine acceleration problem in the critical zone, it is proposed that the proper measures for controlling torsional vibration in the propulsion shafting system should include adjusting the design parameters of its damper instead of using the optimum damper designed from theory in order to prevent fatigue fracture of shafts.

This paper provides an in-depth analysis of alternative fuels, including liquefied natural gas (LNG), hydrogen, ammonia, and biofuels, assessing their feasibility based on operational requirements, availability, safety concerns, and the infrastructure needed for large-scale adoption. Moreover, it examines hybrid and fully electric propulsion systems, considering advancements in battery technology and the integration of renewable energy sources, such as wind and solar power, to further reduce SOV emissions. Key findings from this research indicate that LNG serves as a viable short- to medium-term solution for reducing GHG emissions in the SOV sector, due to its relatively lower carbon content compared to MDO and HFO. This paper finally insists that while LNG presents an immediate opportunity for emission reduction in the SOV sector, a combination of hydrogen, ammonia, and hybrid propulsion systems will be necessary to meet long-term decarbonisation goals. The findings underscore the importance of coordinated industry efforts, technological innovation, and supportive regulatory frameworks to overcome the technical, economic, and infrastructural challenges associated with decarbonising the maritime industry.

This paper aims to identify the best solution for three SOx scrubber systems by evaluating their economic, environmental and technical performances: open-loop, closed-loop and hybrid scrubber systems. It adopted a novel muti-criteria decision-making model which can be introduced as the combination of lifecycle cost and lifecycle assessments, and fuzzy-TOPSIS and fuzzy-AHP. The analysis results of the case study of 72,100 gross-ton cargo ships suggested that the closed-loop scrubber systems would be the most effective in the consideration of all of the aspects, overall. It also shows the excellence of the proposed decision-making model to remedy the shortcomings of the conventional multi-criteria decision-making process by directing the analytic process in a wiser way, by means of fuzzy elements. For the environmental impact assessment, the lifecycle assessment approach enables one to obtain a holistic view of the Lifecycle emissions from the cradle to the grave. This paper finally shows the effectiveness of the proposed method, which can improve confidence in decision-making by extending a short-term view widely. Therefore, it was strongly believed that the proposed model is not necessarily/limitedly applied to marine systems but can be broad and noteworthy for a variety of studies requiring appropriate decision-making.