The takeoff process of a seaplane is different from that of a conventional land-based plane owing to the influence of hydrostatic, hydrodynamic, and aerodynamic forces. As a result, more energy will be consumed by the electric propulsion unit (EPU) of a seaplane during takeoff. Given the limited energy density of contemporary batteries, the energy consumed by the seaplane during its flight mission profile was minimized in this study by improving the efficiency of the EPU using a proposed optimization method. To meet the performance requirements of the seaplane EPU, the pitch angle of the propeller was taken as the optimization variable and the system loss was mathematically modeled. The performance of the EPU was thereby optimized, its consumption during flight was reduced, and the seaplane endurance was increased accordingly. The proposed optimization method was subsequently verified using a prototype test of a twoseat electric seaplane. The results show that the proposed method can reduce the energy consumption of the EPU by more than 5% during a single flight. INDEX TERMSElectric seaplane, electric propulsion unit (EPU), energy efficiency optimization, prototype test. NOMENCLATURE ρ Air density. C T Propeller thrust coefficient. β Propeller power coefficient. S Wing area. C D Aerodynamic drag coefficient. C L Aerodynamic lift coefficient of the aircraft. c r Water friction resistance coefficient. ρ w Water density. B Float width. N P Number of floats. EPU Electric propulsion unit. θ Pitch angle.The associate editor coordinating the review of this manuscript and approving it for publication was Adamu Murtala Zungeru .