Siemens-Schottel Propulsor (SSP)
Podded propulsion unit developed by Siemens and Schottel. It comprises a steerable underwater unit housing a permanent magnet motor directly coupled to two propellers, one ahead of the unit, one astern of the unit turning in the same direction. The use of twin propellers is claimed to boost the efficiency by reducing the load on each individual propeller while the rotational energy from the tractor propeller is recovered as lift and forward thrust on a pair hydrofoil fins angled out from the pod.
The rotor carries permanent magnets while the stator carries the field which is fed from a pulse width modulation (PWM) system in the hull. The stator casing is shrunk into the pod and overhang of the stator windings is encapsulated in a heat conductive material connected to the pod. This means that the heat generated in the motor is conducted to the surrounding water without any need for internal air or water cooling system.
Built at the Chinese Shanghai Edward yard, the product carrier PROSPERO was the first vessel fitted with SSP propulsor.