Hi Chris,
I see the same diver tow units as you.
The super yacht ducted fan is very interesting. With a 25-50m vessel the added drag of the duct is a small percentage of total drag. It might be difficult to scale the duct down enough to maintain this drag ratio? I have read that ducts on the rear of bizjets which were an attempt at quieting take-off noise, ended up producing a boost.
The concern with jamming a 4"X4" through the ducted prop was it having it beat the rudder off. I had already lost one SS rudder that had a 1.5" shaft break off. And it was supported on the bottom by a nylon bearing in a massive skeg.
--- In electricboats@yahoogroups.com, Chris Morriss wrote:
>
> Hi Reid.
> I did wonder about the diver towing units. As far as I know they all
> use a prop-shaft drive from the torpedo body. This makes sense as they
> have to have the long body anyway.
> The rim-drive ring thrusters I am thinking of would be a smaller version
> of those shown in this recent news release:
> http://www.superyachtnews.com/products/18095/schottel_to_develop_superyac
> ht_rimthrusters.html
>
> I guess the URL will be wrapped around, so make sure you use all of it!
>
> These are MUCH larger then anything of interest to us, with the lowest
> power one being 200kW, but you get the idea.
>
> I take your point about jamming of a ducted fan. This is why it needs
> to be fairly easy to lift or swing the unit out of the water for
> cleaning or even un-jamming.
>
> Regards,
> Chris.
>
>
> In message , Reid writes
> >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/
> >
>
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