Chris,
Many years ago I worked on a shallow draft tunnel hull tug named the BIG MAC. Vessels of this configuration were common. 1/2 of the prop was open from the bottom, but the entire prop with in the tunnel. The vessel could be safely beached on any smooth area.
In the 1970's I had a 30" diameter prop built with an integral thrust ring cast on it. Airfoil shape, flat on the outer surface. Although it provided a sizable boost in Bollard Pull, there was no gain when running without a tow. As we operated in water with lots of debris, the risk of getting something jammed in a ringed prop far outweighed any potential gain in thrust.
I am not sure I understand your design of the duct holding the stator, but one would think the drag created from the cross sectional area makes it a non-starter?
Any of the Chinese BLDC motors, which are available up to 10KW could be used in a Stoke Monkey configuration to power a conventional shaft prop; http://www.youtube.com/watch?v=SN3SXISavFw
Motor, controller and throttle are available as a kit.
They could also be used with a suitable thrust bearing and coupling directly on the end of the shaft.
I have a 3KW system, 60V 40Ah. Total cost including Thundersky cells, charger and scooter, $1200. Purchased new on eBay;
http://www.alibaba.com/product-gs/643167780/3000W_Electric_Scooter_3000W_Electric_Motorcycle.html
People smash these up all the time and the end up at scooter dealers or junk yards. Low Budget option?
There are many suppliers of electric aqua tow devices for extending the range of divers. A ducted fan, motor and controller all in the package. Not powerful enough for your application, but perhaps some useful ideas? http://www.scubatow.com/
> Such a thruster would probably require a radial-flux BLDC motor (ring
> stator and inner ring rotor, carrying the multi-blade prop inside the
> rotor ring), as this is best suited to fit the hydrodynamic shape
> required by the duct holding the stator assembly.
> The motor would require two low-friction seals, attached to each end of
> the duct, allowing the rotor to turn, without letting water into the
> rotor/stator gap. Many years ago I saw electric thrusters on a
> remote-controlled inspection submersible that had the motors oil filled,
> but kept pressure balanced by a simple flexible oil-filled bag at the
> water pressure at whatever depth the RPV was working.
>
> I still think that there is a fair-sized market for such a device,
> perhaps in the 3kW to 4kW range. I guess from the fact that no-one has
> mentioned any such unit being on sale means that at the moment, they
> don't exist (or not at any sensible price)? Anyone else reading this
> who might be able to point at a real supplier to the end user?
> --
> Chris Morriss
>
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