## 5 Comparative Evaluation of the Two Motors for Electric Ship Propulsion
PMSMs, due to their higher power density, require advanced cooling solutions such as liquid cooling systems using oil or water to prevent magnet demagnetization and maintain optimal performance. This complexity increases the overall system cost, with cooling expenses accounting for 15-20% of the total investment. In contrast, IMs can operate with simpler air or liquid cooling systems, which are more cost-effective and contribute only 5-10% to the total system cost. This makes IMs an attractive option in applications where cooling infrastructure is limited or cost-sensitive. Insurance and lifecycle costs also play a significant role in motor selection. PMSMs, with their higher initial investment and advanced components, tend to have higher insurance costs due to the potential risks associated with magnet degradation and the need for specialized repair services. Estimated insurance costs for PMSMs range between 5-7% of the initial investment. On the other hand, IMs have lower insurance premiums, typically between 3-5%, owing to their well-established technology, availability of spare parts, and predictable failure modes, which make them easier to maintain and repair. Control and drive systems differ significantly between the two motor types. PMSMs require advanced control techniques such as Field-Oriented Control (FOC) to achieve optimal efficiency and dynamic response, along with sensor-based position feedback for precise control. This results in higher drive system costs, which account for approximately 25-30% of the total cost. IMs, on the other hand, rely on simpler drive control methods such as vector control or field-oriented control without the need for complex rotor position sensors. Their drive systems are more cost-effective, representing around 15-20% of the total cost. Recent studies have also emphasized the energy-saving potential of PMSMs in maritime propulsion through system-level optimization techniques. In particular, [PERSON] et al. [46] demonstrated how PMSMs, when integrated with smart power management strategies, can significantly reduce overall energy consumption and improve propulsion system efficiency. Their findings confirm that, beyond machine-level design, system integration and operational profiles play a crucial role in achieving optimal performance. In addition to passive design improvements, active control strategies can significantly enhance the energy efficiency of PMSM-based propulsion systems. A recent study by [PERSON] et al. [47] proposed an adaptive control algorithm tailored to ship electric propulsion systems using PMSMs. Their method dynamically adjusted control parameters based on operational conditions, such as load variations and navigation modes, to minimize energy consumption without compromising propulsion performance. This approach demonstrated that beyond electromagnetic and thermal optimization, intelligent control systems represent a complementary pathway for further reducing operational costs and increasing propulsion flexibility in maritime environments. Despite their superior performance characteristics, such as higher torque density, reduced maintenance, and greater efficiency, PMSMs face economic limitations due to the high cost of rare-earth permanent magnets. The dependence on rare-earth elements like neodymium and dysprosium not only increases initial investment but also introduces supply chain vulnerabilities, particularly in maritime applications where long-term maintenance is crucial. These economic constraints often lead designers or ship-owners to favor IMs due to the associated lower capital expenditure, especially in small-to-medium tonnage vessels or budget-constrained projects. Although PMSMs involve a higher initial cost due to magnets and complex control electronics, the reduction in ongoing maintenance (no brushes, reduced rotor losses) can lead to a lower total cost of ownership over a typical 20-year vessel lifespan. The break-even point is typically achieved in 5-7 years, depending on operational hours and energy tariffs.