# Multicriteria Analysis of Alternative Marine Fuels in Sustainable Coastal Marine Traffic
## 3 Materials and Methods
### Study Area  
Total length of the Croatian coastline is approximately 6000 km, with islands and islets included. Economic and social development are dependent on coastal marine traffic, which provides frequent connections between the major coastal cities and majority of islands. This is particularly important during the summer, with over 20 million tourists visiting Croatia in 2019. Coastal marine traffic in Croatia connects 73 islands and 22 mainland ports, operating 24 ferry, 15 high-speed, and 13 shipping liner services (52 national lines in total). A combined fleet of over 70 ships provided by 14 Croatian shipping companies is responsible for coastal marine traffic service. Croatia, like many other Mediterranean countries, faces a significant growth in marine transportation. In Table 2, a comparison between Croatia, Greece, Italy, and Spain is shown, where it can be seen that the total number of passengers in 2019 is almost equal to Spain [30]. Considering the number of inhabitants of each country, the ratio between the total number of passengers and inhabitants is shown in the last column, where it can be seen that Croatia has the highest value. The Intergovernmental Panel on Climate Change (IPCC, Geneva, Switzerland) reported that the vast majority of marine propulsion and auxiliary plants on board ocean-going ships are diesel engines, which typically have service lives of 30 years or more. Thus, the IPCC concluded that it will be a long time before technical measures can be implemented in the fleet on any significant scale [31]. A similar situation currently prevails in coastal transportation in Croatia, where ships are mostly equipped with diesel engines. In Figure 2, we showed that the average ship age in Croatia is equal to 30 years, and more than 50% of the ships are more than 30 years old. \begin{table}
\begin{tabular}{c c c} \hline
**Country** & **Total Number of Passengers** & **Passengers per Inhabitant Ratio** \\ \hline Croatia & 34,142,000 & 8.37 \\ Greece & 86,530,000 & 1.43 \\ Italy & 73,930,000 & 6.89 \\ Spain & 34,635,000 & 0.73 \\ \hline \end{tabular}
\end{table} 
Table 2: Comparison between Mediterranean countries in total number of passengers and ratio of passengers per inhabitant [30]. Annex VI to MARPOL, which entered into force in 2005, enacted international legislation related to air pollution from ships and obliged manufacturers and shipping companies to follow the rules stated in Annex VI with regard to ship design and manufacturing, as well as in marine traffic operations. However, most of the ships have been built before the enforcement of Annex VI of MARPOL and it is impossible to modernize or replace the ship fleet instantly and thus ensure marine fuel replacement as an acceptable alternative in satisfying the goals stated in Annex VI and other relevant legal documents. Considering fuel consumption, which is considered to be one of the most significant factors when analyzing the environmental impact of ships through exhaust emissions, Figure 3 presents the analyzed data on age and consumption ratio. It can be seen that a lower fuel consumption is not proportional to decreasing age. This could be misleading since a lower fuel consumption can be the result of a lower gross tonnage in comparison to newer ships. Furthermore, modern engines are improved in terms of satisfying the allowed exhaust emission limits. Expanding marine transportation in Croatia was a motivation to consider the implementation of alternative fuel as an environmental impact mitigation measure. Use of  
Figure 3: The age–consumption ratio of coastal line ships in the Republic of Croatia. Source: Prepared by authors using data provided by [32]. Figure 2: Average ship age distribution in Croatia. Source: Prepared by authors using data provided by [32]. alternative fuels in coastal marine traffic could certainly contribute to sustainable development of the marine environment and coastal area. However, different aspects should be considered during selection of an appropriate marine fuel alternative.