## 3 Materials and Methods
### Split City Port Study Case--Ferry Fleet Energy Demand Analysis  
Split is connected by state ferry lines with ports on the central Dalmatian islands, as shown in Table 2[53,54]. The ferry lines connecting Split with international ports are not taken into consideration in this work. The table shows the average annual number of passengers and vehicles, the duration of sailing in one direction, the number of sailings, and the number of sailing hours on an annual basis. The presented statistical data take into account the period from 2019 to 2022. In order to determine the requirements that must be met by the shore-based power grid, it is necessary to determine the energy needs of ships that use the City Port of Split as one of their base ports. Different approaches can be applied in the analysis of the energy needs of the ferry fleet. The most reliable way would be to analyze the total annual consumption of diesel fuel of the observed fleet. In the observed period, due to the introduction of new vessels, the needs of the operator, and the operational status of the vessel, there were minor changes in the navigation schedule. However, using the list of ships of the Jadrolinija fleet in national and international navigation, in which the annual fuel quotes are listed, the total annual fuel consumption can be determined [51]. The planned annual consumption of diesel fuel by the ferry fleet of the Split waterway for ships that maintain the lines is 15,717,041 L of diesel fuel. Table 3 lists all the ferries of the Split waterway that maintain the observed state ferry lines [53]. The overall length, maximum speed, passenger and vehicle capacity, the line served by the ferry, and the annual fuel consumption rate are shown. First, it is necessary to determine how much useful work can be generated by the fuel used. Modern medium-speed diesel engines have a high degree of useful action, which amounts to about 50% of the energy contained in the fuel [55]. However, in real conditions, only 30-45% of energy is used for useful work [56]. The reason for this is mainly the unfavorable exploitation of the propulsion system. When sailing short distances, a significant part of the time is spent on maneuvering the vessel, which is a mode in which the efficiency of the engine is considerably reduced. Furthermore, it is necessary to consider the average age of the propulsion system of the observed fleet, which is over 23 years [53]. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Line No.** & **Destination** & **Passengers** & **Vehicles** & **Sailing** & **Sailings** & **Sailings** \\  & & **No.** & **No.** & **Duration (min)** & **No.** & **Total (h)** \\ \hline
631 & Supetar (Brač) & 1,684,035 & 399,329 & 50 & 3664 & 3053 \\
635 & Stari Grad (Hvar) & 620,665 & 169,719 & 120 & 1485 & 2970 \\
636 & Rogac (Solta) & 341,128 & 86,797 & 60 & 1611 & 1611 \\
602 & Vis (Vis) & 244,185 & 61,358 & 140 & 780 & 1820 \\  & Vela Luka & & & & & \\
604 & (Korcula)—Ubli & 203,712 & 55,447 & 240 & 880 & 3520 \\  & (Lastovo) & & & & & \\  & Total on an annual basis & 3,093,725 & 772,650 & & 8420 & 12,974 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: State ferry lines of the Split waterway that use the City Port of Split. Diesel fuel compliant with EN 590:2013 (Automotive fuels--Diesel--Requirements and test methods) is used as fuel. The specific density of diesel fuel, according to the EN590 norm, is between 820 and 845 kg/m\({}^{3}\) at 15 \({}^{\circ}\)C, while the typical average value is 835 kg/m\({}^{3}\)[57]. The mass of loaded fuel is calculated according to the formula:  
\[m=\rho\times V \tag{1}\]  
where \(\rho\) is the specific density and \(V\) is the volume of the loaded fuel. Therefore, 16,805,374 L of diesel fuel has a mass of 13,123,729 kg. The upper heating power \(H_{g}\), i.e., the maximum possible energy that can be obtained by burning the fuel used is 45 MJ/kg [58].