## 2 Literature Review  
In order to reduce the emission of harmful gases and the negative impact on the environment, it is necessary to use a comprehensive approach in the design, construction, and exploitation of ships. According to [11], by applying diesel/electric propulsion compared to standard propulsion, significant savings in harmful gas emissions are possible, as well as economic savings on an annual level in the amount of 22%. Electric energy sources for ship propulsion have multiple advantages. Significant savings can be achieved by optimal hull design, which reduces the ship's hydrodynamic resistance. The use of advanced protective coatings reduces the ship's resistance [12]. Additionally, during the exploitation of the ship, the overgrowth of the hull significantly affects fuel consumption [13]. The design and efficiency of the propeller contribute to the reduction of fuel consumption [14]. By choosing the optimal route and sailing speed, savings in fuel consumption are achieved [15]. With the observed type of maritime transport, the navigation route is pre-defined and can be slightly influenced. On the other hand, the speed of the ship significantly affects fuel consumption. Figure 2 shows the relationship between changes in ship speed, which affects the required power of the propulsion engine and, consequently, fuel consumption. For example, as a result of reducing the maximum speed of a ship by 20%, the power consumption and fuel consumption are reduced by 60%. Fuel consumption depends on the type of vessel and its features, but it can be generalized that the power used is proportional to the cubic speed of the vessel. As the ferry sailing routes are relatively short, reducing the peak speed does not significantly affect the length of the journey, as part of the time is spent on maneuvering when entering and leaving the port. Figure 2: Relationship between ship speed, required power, and fuel consumption [16]. The aforementioned technologies and efforts are aimed at increasing the energy efficiency of fossil fuel-powered ships. Of course, the contributions are significant, but the source of energy needed to propel the ship should be renewable with as little environmental impact as possible. In this research, the use of electric energy to propel a ship, more precisely a group of ferries, is proposed. In article [17], a model of a multi-energy ship network with combined power, thermal, hydrogen, and freshwater flows is proposed. By applying the coordinated planning model, the flexibility and practicality of the planning process is increased. Based on the case study, multiple comparative analyses confirmed the effectiveness of the method. In the research [18], energy management and voyage scheduling were modeled with the aim of increasing energy efficiency and reducing greenhouse gas emissions. Unlike previous research, this also took into account the underwater radiated noise generated by the action of the ship's propeller. The model has been verified in real conditions and shows efficiency. Table 1 shows examples of the application of RES on electrically powered ferries. Although there are earlier examples of the use of electric ferries, vessels launched in the period from 2012 to 2023 were taken into consideration.