Voith Schneider Propeller

Cool, similar to helicopters which can also control direction indepentendent of thrust, which leads to RC helicopters being able to pull of crazy, physics-defying moves like here: https://www.youtube.com/watch?v=QSiwyoQldfo

The coolest recent development in marine propellers is toroidal propellers which are now commercially available and seem to perform significantly better than standard propellers: https://www.sharrowmarine.com/

The same article in german has some nice animations: https://de.wikipedia.org/wiki/Voith-Schneider-Antrieb

These were used on three car ferries in Scotland, mostly between Gourock and Dunoon but the same vessels were sometimes used on other routes. The Saturn, Juno and Jupiter which were quite fast and incredibly maneuverable: "...service speed was around 15 knots (although she could also achieve 13 knots astern and 3 knots sideways" with just those drives. No separate screws, bow or stern thrusters. Same drive was used on a few smaller local ferries, too.

If I remember right what they didn't do was go exactly straight. You could see a (very modest) s-shape in the wake over distance.

ref: https://www.shipsofcalmac.co.uk/fleet-features/the-streakers

This reads a lot like an advertisement. The linked page [[Cyclorotor]] is more neutral and has more information on the design and applications outside of marine vessels:

https://en.wikipedia.org/wiki/Cyclorotor

See a tug showing off here: https://www.youtube.com/watch?v=u6uNECa_X8Q Voith is the only company producing those, even though the patent has expired.

I recommend this video with animations : https://www.youtube.com/watch?v=QrBF9BWYAZY

From a resilience POV, my guess would be that failure of any one blade would botch the system overall. Maybe that is why many diagrams show them installed in pairs. (I would guess each operates in a different direction for angular momentum reasons.) I have no idea about overall reliability.

See also https://news.ycombinator.com/item?id=26339421