Several years ago I came across the Schilling ring thruster that a friend of mine helped design in Davis, California. I just posted a really amazing clip on You Tube of two ring thrusters taking turns sucking in and then spitting out a rope to show one of the advantages of the ring thruster.
I think that shot may have been done in Lake Tahoe with the ring thrusters mounted on a ROV. Since then Schilling has partnered up in a sort of merger with Sub-Atlantic and since they have a large line of standard thrusters Schilling Robotic put the ring thruster on hold. They will only supply parts for the units they already manufactured.
The ring thruster gets rid of what I've been told is the Taurus effect you get on standard props when the water swirls around to outer area of the prop like a donut and you lose something line 30% of your efficiency to it which is why you see so many shrouded props being made lately. The ring thruster compresses the water into the middle in a way that Fleetwater Marine is claiming the ring thruster will not produce any cavitation. I don't know enough about it to say for sure. I called Schilling a while back to get a price and they didn't have much data for me but they made it sound very expensive since they used to only sell them as a package deal with all the computer controllers.
The basic design was bought from Russia and so far I have not found the U.S. Utility Patent for it yet. I've seen two other prototypes from other companies but as far as I know their are not in production at the moment. I would love to see this technology get going again.
Harbor Branch Oceanographic Institution, Inc. Had a prototype up on there site as well but I'm not able to find it just now.
I'll get some pics posted here in a little bit.
Brent Hartwig