Comment by ChrisMarshallNY
5 years ago
That's cool. I never knew about these.
I suspect that efficiency, and probably speed, are sacrificed for maneuverability.
It would certainly require a great deal of maintenance. Anyone that has ever dealt with marine, knows that anything that touches seawater needs a lot of TLC, and it looks fairly complicated (compared to screws).
They're actually highly efficient. More efficient than screw propellers. They have very large surface areas, and move at uniform speed through the water. Screws spin very quickly at their tips, very slowly at their base, and the sweet spot in the middle is the only prime area for converting energy to propulsion. The fast moving parts generate significant drag, the slow moving parts generate insufficient forward propulsion for the drag they generate. VSPs do not have this disadvantage.
They are, of course, as you pointed out, a goddamned nightmare for maintenance. Lots of moving parts. Lots of seals. Lots of mechanical parts in contact with saltwater.
They're generally only used on tugboats, because tugboats must be able to point in one direction, but apply force in a different direction. And they must be able to change which direction they're applying force on a dime. And if and when tugboats break down -- they're already in a port. If a tugboat breaks down they've by definition not stranded in the middle of nowhere. Which mitigates the maintenance nightmare significantly.
Many short-distance (< 30 km) ferries in the UK that sail in busy waters (i.e. harbours, ports) have them, and generally they're very reliable and low-maintenance.
One of the disadvantages are the draft required, and it is a concern for grounding, so many have plates underneath for protection.
I hadn't heard before about ferries using Voith Schneider propellers. I did know that many ferries use (somewhat more traditional) azimuth thrusters for good maneuverability.
My local ferries use them: https://www.doverferryphotosforums.co.uk/new-mv-wight-light-...
Also used by the short-range ferries in Stockholm's Hammarby Sjöstad. Source: have travelled on these many times and observed the weird wake.
These are used on tugs for the most part, which has the requirement to apply thrust immediately to any direction so you can control the motion of a larger vessel easily. I'm not sure about efficiency, but they're fun to drive.
They seem to be the mecanum wheel of the sea, another high maintenance, low durability locomotion method.
That's inconsistent with the increasing usage described in the article.
I was thinking the same thing, and it’s certainly true functionally, but the mode of operation is quite different. It’s not about combining force vectors from different wheels, instead each blade rotates to always be thrusting in the desired direction.