Podded Drives

Introduced relatively recently podded drive systems have become more and more common especially in the passenger ship market
They offer combined propulsive and steering ability thereby simplifying the stern arrangement. In addition they may be fitted relatively late is the ship build and remove the need for shaft alignment.
The plant layout may be optimised for the vessel type.

Construction

The pod is allowed to rotate on a rolling element slew bearing driven by either an electric or more commonly hydraulic motor via a gear ring. Electric power si supplied via slip rings to an electric motor mounted in the pod. This electric motor drives one or two fixed pitch propellers.
manouevring is a achieved by modulation of the power supply. More recent developments have seen the use of single propellers arranged so that in normal running they are in pulling mode sitting ahead of the pod. This has been shown to increase propulsion efficiency.

Operational Difficulties

The removal of gearing from these units allows for increased operational reliability. They are air cooled and therefore require large volumes of air to cool. This can introduce sea water and salt laden air into the windings and lead to overheating and corrosion. Slip rings must be properly maintained otherwise can be a potential source of failure.
The units are relatively exposed and may be susceptible to impact damage