## 5 Comparative Evaluation of the Two Motors for Electric Ship Propulsion
Also, the rods used in the induction motor presented a significantly greater mass than that of the magnets carried in the PMSM. (v) Based on the geometric parameters defined in Table 5 and the surface-mounted magnet topology illustrated in Figure 8, the total magnet mass was calculated for the 10.2 MW PMSM design. Using the average rotor diameter D\({}_{\rm r}\) = 1349.9 mm, magnet height \(h_{m}\) = 22.2 mm, pole coverage ratio \(\alpha_{p}\) = 0.8533, and axial stack length L = 1.5 m, the resulting total volume of magnet material was approximately V = 0.119 m\({}^{3}\). Assuming a standard NdFeB magnet density of 7400 kg/m\({}^{3}\), the total magnet mass was estimated to be 882 kg. This quantification is critical for evaluating material costs and for understanding the thermal inertia introduced by high-density magnetic components. The result also validates the non-linear growth trend observed in Figure 8, where increasing the D/L ratio led to disproportionate increases in the required magnet volume due to elevated torque demands and flux density constraints. A comprehensive analysis comparing PMSMs and IMs for 10 MW electric ship propulsion revealed significant differences in various aspects, including materials, operational efficiency, maintenance requirements, cooling systems, insurance costs, and control strategies. PMSMs utilize high-performance rare-earth permanent magnets, primarily Neodymium-Iron-Boron (NdFeB), which contribute substantially to their high costs due to the scarcity and geopolitical constraints surrounding these materials. Additionally, PMSMs require high-quality laminated silicon steel for stator cores to minimize core losses and advanced copper windings with superior insulation to achieve high efficiency. The estimated material cost share for PMSMs is approximately 60% of the total motor cost, reflecting the cost of rare-earth materials and complex manufacturing processes. In contrast, IMs employ more cost-effective materials such as copper or aluminum windings and squirrel-cage aluminum or copper bars for the rotor, which simplifies the manufacturing process and reduces initial costs. The estimated material cost share for IMs is around 40% of the total motor cost, benefiting from lower material costs and mass production advantages. The complex assembly and precision magnet placement in PMSMs lead to higher production expenses, whereas IMs benefit from simpler and more cost-efficient mass production methods. In terms of operational efficiency, PMSMs achieve efficiencies of up to 97-98%, significantly reducing energy losses and offering lower copper losses since they do not require rotor current. This results in lower lifetime energy consumption and improved torque characteristics with minimal ripple, leading to smoother propulsion and reduced energy fluctuations. On the other hand, IMs exhibit slightly lower efficiency levels, typically around 93-95%, with higher power consumption over their operational lifespan due to slip losses and secondary current requirements. The operational cost savings provided by PMSMs can translate into a fuel consumption reduction of 5-8% over a period of 20-25 years, making them a more energy-efficient option despite the higher initial investment. Maintenance requirements differ significantly between PMSMs and IMs. PMSMs have fewer mechanical components such as brushes and slip rings, leading to lower maintenance demands and higher reliability. However, they require periodic monitoring to prevent thermal demagnetization and insulation degradation due to high-speed operation. IMs, conversely, demand more frequent maintenance due to the presence of rotor windings and potential bearing failures. The squirrel-cage rotor design in IMs, while robust, may experience bar breakage over time, leading to increased maintenance interventions and higher downtime costs. Overall, PMSMs have approximately 30% lower maintenance costs compared to IMs, contributing to their long-term economic viability. Cooling systems are another critical factor to consider in such a comparison.