# Environmental and Economic Aspects of a Containership Engine Performance in Off-Design Conditions
## 1 Introduction  
In light of climate changes, significant pressure is put on the maritime industry to decarbonize as soon as possible. With the adoption of many regulations, the industry is urged to increase the energy efficiency of newly built and existing ships. Within the revised Strategy on Reduction in GHG Emissions from Ships adopted by the International Maritime Organization (IMO) in 2023, the goal is set to reach net-zero GreenHouse Gas (GHG) emissions from international shipping by 2050, with a commitment to ensure an uptake of alternative zero and near-zero GHG fuels by 2030 [1]. CO\({}_{2}\) emitted by international shipping per transport work must be decreased by at least 40% by 2030 compared to 2008. Additionally, the legislative bodies of the European Union (EU) have reached an agreement to include ships above 5000 GT in its Emission Trading System (ETS), under which each company with ships operating in the area under EU/EEA is required to report and verify its GHG emissions through the existing EU MRV (Monitoring, Reporting and Verification) system [2]. The regulation comes into force in 2024, and penalties of EUR 100/ton CO\({}_{2}\) will be applied to companies that fail to report the emissions. Companies that fail to comply with the regulations may be denied entry into the EU. On the other hand, the adequacy of regional implementation of ETS becomes questionable due to carbon leakage, considering that liner shipping is cross-regional by nature [3]. The maritime transport industry should find the most effective way to decrease CO\({}_{2}\) emissions and eventually become carbon neutral [4]. Alternative fuels such as methanol, ammonia and methane-hydrogen blends are currently receiving the most interest as greenfuels enabling energy transition in the maritime sector [5; 6]. [PERSON] et al. [7] concluded that renewable-energy-based synthetic fuels can compete with conventional diesel fuel from 2040. IMO proposed several measures to increase the energy efficiency of ships that can be divided into technical and operational measures [8]. The operational measures apply to existing ships and can be short-, mid-, and long-term based on the length of their application. To meet these measures, shipowners should modernize their fleets but are facing the challenge of having ships too old to retrofit and too young to scrap [9]. Complying with the Energy Efficiency Existing Ship Index (EEXI) and Carbon Intensity Indicator (CII) regulations can be extremely challenging for ships that are powered by engines fueled with marine diesel oil and heavy fuel oil [6; 10; 11; 12]. The majority of the existing Post Panamax, Post Panamax Plus and Very Large Containerships built before 2016 do not meet the novel EEXI requirements [13]. For containerships, a speed reduction of approximately 40% would be sufficient to reach the target set by IMO to reduce CO\({}_{2}\) emissions by 50% up to 2050 in comparison to 2008 [14]. It is expected that the introduction and compliance with measures intended to increase the energy efficiency of ships will lead to lower sailing speeds and altered effective capacity supply. According to ships' operating profiles, slow steaming as one of the short-term measures is already being applied. Shipowners and ship operators apply slow steaming when the market demand and freight rates are low, and fuel costs are high. Even though slow steaming is associated with environmental benefits, none of the shipping companies recognize the positive effects on the environment, but only the increased costs that customers are not willing to bear [15]. Shipowners and ship operators will reduce speed in case fuel cost savings outweigh the incurred capital and operating costs [16]. Sailing at lower speeds leads to a decrease in fuel consumption and consequently CO\({}_{2}\) emission [17]. However, the extended delivery time as well as higher inventory burden should be considered as well [18]. The yearly transport work should be kept constant while considering the benefits of the application of slow steaming.