# Economic Feasibility of Retrofitting an Ageing Ship to Improve the Environmental Footprint
## 1 Introduction  
The recent estimates of the Fourth International Maritime Organisation (IMO) Greenhouse Gas (GHG) Study 2020 [1] show a troubling message for shipping Greenhouse Gas emissions. There was a 9.6% increase in GHG emissions from 2012 to 2018, mainly due to a continuous increase in global maritime trade. The share of shipping emissions also increased from 2.76% in 2012 to 2.89% in 2018. The activities of IMO addressing climate change started more than ten years ago by signing a Cooperation Agreement between IMO and the Korea International Cooperation Agency (KOICA) on April 2011 for the implementation of a technical cooperation project on Building Capacities in East Asian countries to address Greenhouse Gas Emissions (GHG) from Ships [2]. In recent years, numerous resolutions and documents have been adopted [3] to achieve the ambitious goal of a 50% reduction in the total annual GHG emissions and 70% reduction in CO\({}_{2}\) emissions per transport work compared to 2008 by 2050. For the implementation of these goals, several mandatory instruments for new and existing ships have been proposed, such as the MARPOL Annex VI, with the Energy Efficiency Design Index (EEDI) introduced increasingly strict carbon intensity standards for new ships and the Ship Energy Efficiency Management Plan (SEEMP) for operators to improve the energy efficiency of all ships and, additionally, the Energy Efficiency Operational Indicator (EEOI), Energy Efficiency Existing Ship Index (EEXI) and Carbon Intensity Indicator (CII). Generalisations and guidelines for increasing the energy efficiency of ships have appeared after the first approved requirements [4]. They were in several groups: Hull form optimisation; Energy-saving devices; Structural optimisation and light-weight construction; Machinery technology; and Fuel efficiency of ships in service. Several examples of structural optimisation and light-weight construction can be seen in [5; 6; 7; 8; 9] and for control of ship operation due to the generated air pollution by ships in coastal water in [10; 11; 12; 13]. The development of machine technologies is also related to the introduction of alternative fuels. Even in the early years, special attention was paid to Liquified Natural Gas (LNG) [14; 15; 16]. The LNG is cleaner than coal or oil and its use as fuel in shipping leads to a reduction in NO\({}_{x}\), SO\({}_{x}\) and CO\({}_{2}\) emissions. This is of great importance for operations in the Emission Control Area (ECA), where 18.5% of handy-size tankers and small and medium size Ro-Ro spend 80% of their sailing time [15]. The use of LNG complies with ECA regulations as sulphur oxides emissions are reduced to zero. The nitrogen-oxide emissions are below the Tier III regulation, applicable in ECA from 2016, and it is very low in particles reducing at the same time the carbon dioxide emissions in the range of 20-25% [16]. A comparison of LNG's life cycle environmental performance, liquefied biogas (LBG), methanol and bio-methanol are presented in [17], where four aspects are considered, i.e., technical, economic, environmental and other. The last group are safety and safe handling, availability, public opinion, etc. Although liquefied natural gas or methanol produced from natural gas significantly improves environmental performance, the impact on the climate is of the same order as using heavy fuel. There will be a more significant effect when using methane and methanol produced from biomass. Alternative fuels, in combination with additional equipment, are an option to meet the requirements of ECA [18]. A comparison of three alternatives: Heavy Fuel Oil (HFO) combined with a scrubber and a Selective Catalytic Reduction (SCR), Marine Gasol (MGO) combined with an SCR and LNG shows that none of them leads to less impact on the climate than heavy fuel. Reducing the methane slip to 2 wt.% (weight percentage) would ensure that LNG has a lower impact on climate change.