The shipping industry is becoming increasingly aware of its environmental responsibilities in the long-term. In 2018, the International Maritime Organization (IMO) pledged to reduce greenhouse gas (GHG) emissions by at least 50% by the year 2050 as compared with a baseline value from 2008. Ammonia has been regarded as one of the potential carbon-free fuels for ships based on these environmental issues. In this paper, we propose four propulsion systems for a 2500 Twenty-foot Equivalent Unit (TEU) container feeder ship. All of the proposed systems are fueled by ammonia; however, different power systems are used: main engine, generators, polymer electrolyte membrane fuel cell (PEMFC), and solid oxide fuel cell (SOFC). Further, these systems are compared to the conventional main engine propulsion system that is fueled by heavy fuel oil, with a focus on the economic and environmental perspectives. By comparing the conventional and proposed systems, it is shown that ammonia can be a carbon-free fuel for ships. Moreover, among the proposed systems, the SOFC power system is the most eco-friendly alternative (up to 92.1%), even though it requires a high lifecycle cost than the others. Although this study has some limitations and assumptions, the results indicate a meaningful approach toward solving GHG problems in the maritime industry.

The primary electric power system of ships has been based on the alternating current (AC) system for a long time. However, marine engineers started to question the efficiency of the AC-grid system, which was previously taken for granted and attempted to find a more efficient and eco-friendly electric power distribution system. Following this trend in the marine industry, the direct current (DC) system was adopted for the electric distribution system in ships and combined with the AC-grid. In this regard, this paper presents the technical, economic, and environmental benefits of the DC-grid system for marine applications. Ships that have already applied or plan to apply the DC-grid system are categorized into several types. Additionally, some technical considerations focused on the fault protection topology, the power-sharing (balancing) topology, power quality/stability issues, power source control methods, DC arc flash hazard, and international regulations/standards regarding DC-grid ships are reviewed. Lastly, the prospects of the DC-grid system in ships are addressed with a conclusion.

Liquefied natural gas (LNG) is recognized as a preferable alternative fuel for ship owners, since it can substantially reduce harmful emissions to comply with stricter environmental regulations. The increasing number of LNG-fueled vessels has driven up the number of LNG bunkering vessels (LNGBVs) as well. A key issue of LNGBVs is boil-off gas (BOG) generation, especially the huge amount of BOG that is generated during loading and unloading (bunkering) processes. This study proposes a hybrid system that combines conventional onboard LNG-fueled generators with an energy storage system (ESS) to solve the BOG issue of LNGBVs. This hybrid system is targeted at an LNGBV with the cargo capacity of 5000 m³. The amount of BOG generation is calculated based on assumed operation modes, and the economic study and the environmental analysis are performed based on the results. By comparing the conventional system to the proposed ones, some benefits can be verified: about 46.2% BOG reduction, 66.0% fuel saving, a 7.6-year payback period, and 4.8 tons of greenhouse gas (GHG) reduction for one voyage in the best case, with some assumptions. This proposed hybrid system using the ESS could be an attractive green solution to LNGBV owners.

Concerns about harmful exhaust emissions from ships have been an issue. Specifically, the emissions at ports are the most serious. This paper introduces a hybrid power system that combines conventional diesel generators with two different energy storage systems (ESSs) (lithium-ion batteries (LIB) and supercapacitors (SC)) focused on port operations of ships. To verify the proposed system, a bulk carrier with four deck cranes is selected as a target ship, and each size (capacity) of LIB and SC is determined based on assumed power demands. The determined sizes are proven to be sufficient for a target ship through simulation results. Lastly, the proposed system is compared to a conventional one in terms of the environmental and economic aspects. The results show that the proposed system can reduce emissions (CO₂, SO_X, and NOx) substantially and has a short payback period, particularly for ships that have a long cargo handling time or visit many ports with a short-term sailing time. Therefore, the proposed system could be an eco-friendly and economical solution for bulk carriers for emission problems at ports.

As the maritime industry’s emphasis on sustainable fuels has increased, liquid hydrogen (LH₂) has emerged as a promising alternative due to its high energy density and zero-emission characteristics. While the experience of using natural gas in ships can serve as a basis for the introduction of hydrogen, the different risks associated with the two fuels must also be considered. This review article provides a methodology for selecting suitable metal materials for shipboard LH₂ storage and piping systems based on operational requirements. The effects of both liquid and gaseous hydrogen environments on metal materials are first comprehensively reviewed. The minimum requirements for metal materials in liquefied natural gas (LNG) storage systems, as stipulated in the IGC and IGF codes, were used as a baseline to establish minimum requirements for liquid hydrogen. The applicability of austenitic stainless steel, a representative metal material for cryogenic use, to a liquid hydrogen environment according to nickel content was examined. In order to apply liquid hydrogen to the marine environment, the minimum requirements for liquid hydrogen were organized based on the minimum requirements for metal materials in the LNG storage system covered by the IGC and IGF codes. Finally, to expand the material selection criteria for low-temperature cargo and fuel storage facilities at sea, slow strain tensile testing, fatigue life, and fracture toughness considering the hydrogen environment and cryogenic temperature were derived as evaluation items.

The present study investigates the strain-rate-dependent mechanical performances of three different kinds of polymers in low-temperature applications, including plastic piping systems. Recently, lightweight constructions have been increasingly used in ship and offshore structures because using low-density materials reduces the structural weight of products. However, most of the existing research outcomes have not focused on low-temperature applications. In the present study, the mechanical and failure characteristics of acrylonitrile butadiene styrene (ABS), polyethylene (PE), and polyvinylidene fluoride (PVDF), which are the most widely used in ship and offshore industries, were tested under low-temperature conditions. The quasistatic tensile stress–strain responses of the polymers were observed at rates of 10⁻², 10⁻³, and 10⁻⁴ s⁻¹. As the temperature decreased, the tensile strength and Young’s modulus of tested polymers increased. The fracture strain and modulus of toughness of ABS were considerably lower than those of PE and PVDF at room and low temperatures. When compared with mechanical properties, PVDF displayed superior capability, and each polymer showed different fracture surface characteristics, such as ductility and brittleness. The quantitative material properties tested at various temperatures and strain-rates can be used as material information for the finite element (FE) analysis and material parameters for the development of advanced constitutive models.