TECHNOLOGY
The Inovelis Pump Jet Pod
D
uring his presentation at the Mari-Tech 2011 Conference, Gene Joelson, Converteam Canada Inc. started by providing some background on Converteam, noting that the company was spun off from the power conversion team of Alstom in 2005 and has been identified for acquisition by General Electric Energy. The transaction should be completed this summer. Converteam designs and builds rotating machines (motors and generators) as well as variable frequency drives and are masters at control and automation. Converteam then takes those three elements and integrates them together for various applications throughout a number of industries — cruise ships, international navies, offshore oil rigs, steel mills, pipelines, wind turbines, etc. The pod propulsion system provides for improved maneuverability, reduced powering requirements, increased on-board volume, reduced noise and vibration and modular repair and replacement. The latest development from Converteam is the Inovelis / Pump Jet Concept which was borne out of naval submarine technology. The Inovelis is a pushing pod as opposed to a pulling pod and is characterized as a very compact system. The main differentiating features of an Inovelis pod compared to a conventional pulling pod include: • a simple hydrodynamic system that uses a nozzle to increase efficiency from bollard pull to open water efficiency at transit speed ( higher open water efficiency, higher hull efficiency) • a homogenous blade loading that reduces the pump jet rotor diameter for a compact propulsor. • a better capabilities for maneuvering at low speed and sea keeping at transit speed thanks to the nozzle. 52 BC Shipping News July/August, 2011
• a very low level of pressure pulse as the nozzle acts as a screen in front of the hull, reducing tip clearance for better hull integration. Gene outlined how the Inovelis, two generations beyond a regular shaft propeller, enables the hull to be designed for greater efficiency. The difference between a conventional pulling pod and the Inovelis pod is that the conventional pod requires an incline which means a loss of thrust. The blades of the propeller on a conventional pod create pressure pulses which strike the underside of the hull which contributes to noise. Converteam has put significant effort into reducing that noise, especially for cruise ships. Also, there is an area of low pressure on the hull ahead of the conventional pod which increases the drag – another thing that contributes to lower efficiency. With the Inovelis pod, the line of thrust is horizontal – being a pushing pod, the propellers move further away from the underside of the hull and can be optimized for cleaner hydrodynamic flow into the thruster.
Additional differences — and hence benefits — to the Inovelis pod over the conventional pod are related to simplicity - electrical steering (rather than hydraulic), integrated seating for ease of installation by the shipyard, bi-lateral cooling for homogeneous temperature gradient, a high torque density induction motor rather than a more complex synchronous motor that requires a rotor mounted exciter, and marine proven sleeve bearings for the shaft line. For inspection and maintenance the larger Inovelis pods provide access from inside the ship for a typical size technician (this is not the case for smaller, compact Inovelis pods ranging from 2 to 5 MW). The Inovelis pods range in sizes from two to five MW (a compact pod suitable for a yacht, tug, and smaller ferries) up to a range of five to 21 MW which would be found in cruise ships, large ferries and tankers for example. Gene used a case study of a Ro-Pax ferry in France, noting that the advantages due to the Inovelis pod included improved propeller efficiency and ef-