Propeller and thruster manufacturer Brunvoll in Norway and fellow Norwegian company Norpropeller AS have revealed details of a new type of propulsor they are working on that employs the rim-drive, rather than hub-drive concept. The two companies have been working together on the Rim Driven Thruster (RDT) since 1992, and recently concluded the latest in a series of tests that have seen Brunvoll build and conduct successful trials with a 100kW azimuthing RDT.
In the RDT, the rotor bearings are located at the periphery of the rotor and a fixed pitch propeller is connected directly to the rotor and hence has no central shaft.
Brunvoll is planning to market the RDT for ships and larger craft, whilst Norpropeller focuses on the market for smaller craft.
They anticipate that the RDT will have a number of significant advantages:
1. The bearings of the RDT are designed in such a way that oil lubrication is not required, and there are no dynamic seals, minimising maintenance costs.
2. The RDT design developed by the two companies has no central shaft and no supporting struts so water inflow to the propeller is more uniform and undisturbed, which is beneficial with regard to efficiency and propeller induced noise and vibration.
3. Eliminating the central shaft and shaft support stays, along with any dynamic seals, is beneficial with regard to damage from lines and ropes that could become caught in a propulsor.
4. Eliminating the gap between the propeller tips and the duct or tunnel enhances the efficiency of the propeller, and reduces noise levels. The thickness of the propeller blade can be reduced, and the distribution of the radial thickness and the radial load distribution can be modified to enhance the propeller's efficiency.
Follow this link to click on the PDF file with extensive images and specs (worth a look)...
http://www.brunvoll.no/Web/webPublis...C?OpenDocument 
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