## 1 Introduction  
Nowadays, much effort is being focused on increasing efficiency and reducing harmful emissions. Modern propulsion systems are an emerging technology being applied to electtify transportation [1, 2]; similar efforts have been applied to other industries, such as elevators, aerospace, ships [3], and electric vehicles [4]. Electric motor manufacturers have focused on producing suitable subsystems such as batteries, power electronics, and electrical machines. Traditional propulsion systems suffer from several limitations, e.g., low efficiency, high fuel consumption, and elevated emissions. Additionally, they require large installation spaces and offer limited maneuverability [5]. In contrast, the use of electric motors provides advantages such as reduced fuel consumption, reduced maintenance requirements, smaller volume for propulsion systems, and flexibility in space utilization, thereby increasing a ship's payload, improving ship handling during low-speed movements in shallow waters and during embarkation/disembarkation phases, and reduced noise and vibrations, resulting in a significantly improved experience for the crew and passengers of the ship [6]. These features have led to the integration of electric motors contributing to the generation of electricity, as parts of auxiliary systems, and as the main propulsion engines of ships' propeller [7]. In the case of electric generators, significant research has been devoted to their design and control. Advanced algorithms have been developed to manage ship power more efficiently, taking into account electric machine behavior, operational constraints, and environmental conditions. These strategies aim to reduce both fuel consumption and costs [8]. Electrical machines are the main propulsion units in hundreds of ships of different types, such as cruise ships, ferries, pleasure boats, warships, fishing vessels, icebreakers, and research vessels [9]. At the same time, research is being carried out on the use of electric propulsion in new vessel designs. Nowadays, integrated electric ships have become increasingly attractive for commercial fleets. This shift is driven by advances in power electronics, improvements in electric motor design, and the emergence of new propulsion architectures. These systems provide notable advantages compared to conventional axial propulsion [10]. Research has shown that the use of electric propulsion is limited to high-volume vessels such as cargo and box ships, tankers, LNG carriers, and chemical carriers, due to their high investment costs [6] and environmental impact [11]. Effective propulsion systems should demonstrate high efficiency and a suitable power factor. They must also exhibit low losses, acceptable thermal behavior, and minimal cogging torque and torque ripple [12]. Also, they must have a high power and torque density, as the installation space for motors is limited [13]. Different topologies of electric motors have been investigated in order to determine their suitability for specific applications. Among these categories are induction motors (IMs) [14], permanent magnet synchronous motors (PMSMs) [15], high temperature superconducting motors (HTSMs) [16], high efficiency super drive systems (HESDSs) [17], and acyclic coaxial motors [18]. The first two categories are the most widely used technology. Their specific characteristics and advantages are well known and have been documented in numerous published scientific papers [19]. At this point, it should however be pointed out that modern motors carrying either internally or surface mounted magnets can be used just as effectively. As highlighted [20], the power and torque transmitted to a ship's propeller reach their maximum values when the rotational speed achieves its peak level. Achieving this condition depends on the optimal operation of the propulsion system, efficient energy management, and the minimization of losses in both mechanical and electrical subsystems [21].