## 3 Case Study: Purse Seiner in the Adriatic Sea  
### Ship Particulars and Operative Profile  
The Croatian fishing fleet consists of 7808 fishing vessels, whose fishing activities result in nearly 6% of the total catch in the Mediterranean area. Vessels of less than 6 m in length constitute 56.4% of the fleet, while 36.4% of the fleet are vessels between 5 and 12 m long. However, purse seiners 24 to 40 m in length are responsible for 55% of the landing value and 90% of the lending weight [89; 90]. The main particulars of the considered purse seiner are presented in Table 4.  
Fuel consumption during fishing trips highly depends on the operating profile, which for a purse seiner involves several steps, as presented in Figure 4. \begin{table}
\begin{tabular}{c c} Length overall, (m) & 32.28 \\ \hline Breadth, m & 7.40 \\ \hline Drawth, m & 2.88 \\ \hline GT & 182 \\ \hline Main engine power, \(P_{ME}\) (kW) & 480 \\ \hline Installed auxiliary power, \(P_{AE}\) (kW) & 370 \\ \end{tabular}
\end{table} 
Table 4: Main particulars of considered purse seiner [89]. Figure 3: Carbon taxation scenarios. Data on operating times are crucial for investigating the energy consumption of purse seiners. Their working time varies daily and depends on weather conditions and fish season (and on whether catch limitations are in force) [91]. A typical purse seiner follows the timetable detailed in Figure 4: starting the fish trip at time \(t_{0}\), cruising to the open sea till time \(t_{1}\); then, the fishing operation, i.e., harvesting the fish, occurs till time \(t_{2}\), when the purse seiner starts to return to the port. A number of Croatian fishing vessels were equipped with a fuel monitoring system, GPS, and accessory switches by the authors, providing information about their use of particular engines (main and auxiliary engines). The monitoring system was connected to the software \"MAPON\", which collects real-time data on the fishing trip (route, time, location, etc.) [92] (Figure 5). Using data from MAPON, the load profile of a purse seiner on a random fishing trip is presented in Figure 5. It describes how much time the ship spends at which engine speeds and loads, and it relates only to the main engines. Bearing in mind that fishing vessels do not operate on fixed routes and their fishing trips vary, an average ME load of 56% is used within this paper. [PERSON] et al. [93] investigated the operating profiles of several Croatian fishing vessels (purse seiners and trawlers) with MAPON and concluded that for purse seiners, the average daily operating time of the main engines (\(t_{ME}\)) is four hours, while for auxiliary engines (\(t_{AE}\)), it is 15 h. Due to limitations of work quotas (20 days per month) and the suspension  
Figure 4: Typical operating profile of a purse seiner. Figure 5: Load profile of a purse seiner on a random fishing trip. of fishing due to the restoration of fish stock, they reported the operating time during the year to be around 200 days [89]. The average power of a ship, \(P_{ave}\) (kW), that is required for the ship's operation (propulsion, fishing, hotelling, gear, etc.) is calculated with the following equation:  
\[P_{ave}=P_{ME,ave}+P_{AE,ave}\, \tag{6}\]  
where \(P_{ME,ave}\) (kW) is obtained by multiplying the power of a main engine by 0.56 (average load of 56%), while \(P_{AE,ave}\) (kW) is calculated according to the following equation [93]:  
\[P_{AE,ave}=0.388\cdot P_{ME,ave}. \tag{7}\]  
Furthermore, the energy consumption of a ship, \(EC_{A}\) (kWh), is calculated on an annual basis as follows:  
\[EC_{A}=P_{ME,ave}\cdot t_{ME,A}+P_{AE,ave}\cdot t_{AE,A}\, \tag{8}\]  
where \(t_{ME,A}\) (h) and \(t_{AE,A}\) (h) refer to the annual operating time of the main engine and auxiliary engines, which equal 800 h and 3000 h, respectively. The energy needs and ECA for each considered alternative power system are equal to those for the existing diesel-powered ship. Currently, fishing vessels in Croatia are completely powered by diesel fuel.