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Abstract
Azipod® propulsion is a gearless steerable propulsion system where the electric drive motor is located outside the ship hull in the pod housing. The shaft is directly connected to the electric motor driving the propeller. The Azipod ® propulsion units can be steered 360 degrees using a steering system located inside the ship hull. Due to this arrangement, the electric drive motor becomes a significant underwater noise source as it is located outside the ship hull. Propeller hydrodynamic noise is another important noise source in propulsion. Especially, when exceeding the cavitation inception speed, hydrodynamic noise becomes equally or even more important underwater radiated noise (URN) source as the electromagnetic noise. The inflow to the propeller is smooth in pulling Azipod ® propulsion helping to control cavitation and to delay the inception speed. This paper discusses noise measurement-, prediction- and mitigation methods for electric motor emitted URN (MURN) and propeller emitted URN (PURN).