‘rotor sails’ to cut global shipping’s fuel consumption

[Jack Rainbow]

An article by Market News Business offers rotary sails to reduce oil tankers' fuel consumption. I am very weak on science and maths and ignorant about most things mechanical and electrical and I rely on specialists to tell me the truth. I remember over 25 years ago having a big discussion in my local pub about this exact issue, a fictional story I was reading showed a diagram of a ship that had these rotary sails fitted and it included a rough linkage system showing how the horizontal rotation could be converted to vertical rotation to drive propellers. A tool setter from a local factory explained to me it would never work. Mechanical efficiency would be lost, he said, in the conversion. The remaining power available would be too weak to turn the screws. And when you think about it, doesn't it remind you of the 1,200 K/hr hyperloop in its cranky resonance "rotary sails to drive oil tankers"? But, I could be completely wrong, maybe someone here who knows this kind of stuff will tell me it is actually feasible.

 

[MikeG]

I read about this idea some 40 odd years ago. There must be a good reason why it isn't in everyday practical use. The obvious thing is to use them as generators powering supplementary electric motors aiding the main engines.

The idea was never to be to sole power source for the ship, but to reduce its fuel consumption. Knock say 10% of the fuel costs and that could be quite a big deal over a year.

 

[bruto]

I've seen rotary sail designs for many years, but I was under the impression that these are meant for direct propulsion, not power conversion. I believe some successful designs were made even in the 1920's, but that the main problem at the time was economic. The things worked, but not with sufficient efficiency. Remember that a part of a ship's efficiency comes from how quickly it can go, and how much one pays the crew to do it.

Supposedly, the obvious inability to reef is made less of a problem by the ability of a rotor sail to beat directly into the wind, but I suspect that in really bad weather of the sort where complete reefing would be required, this might turn out to be a problem. The infrequency of the event might well be offset by the complete disaster if a bad storm sinks the ship!

However, I have seen recent revivals of this, more oriented, I think, toward auxiliary propulsion of conventionally powered vessels. As energy prices go up, it seems likely that the tradeoff may change.

The aerodynamics of rotary sails appear to be a little counterintuitive, so cautions might or might not be realistic. On the other hand, this is one of those things that's been on the horizon now for nearly a hundred years, and yet never quite practical enough to adopt, and I suspect that some problems remain that make the whole thing, if not impossible, too expensive.

One is reminded that, before the invention of steam powered omnibuses, a number of seemingly well informed engineers were entirely convinced that a powered wheel would simply dig into the ground rather than propel the vehicle forward, and some of the first steam omnibuses were powered by reciprocating hooves to prevent this.

For more on this, look up the "magnus effect," which is the same aerodynamic effect that gives us curve balls, and "flettner rotors," which are what rotor sailing vessels use.

 

[casebro]

I thought it was just a huge rotating drum that acts like a sail, drawing the ship forward.

And 40 years ago is about right.

ata.Ninja'd by Bruto.

 

[rjh01]

Look at the amount of sail required for a ship before engines could be used. In modern terms they would be small ships. So to carry enough sails (or other technology to utilise the wind to power the ship would be huge.

 

[William Parcher]

Is this the same thing that Cousteau's Calypso had at one time?

 

[Trebuchet]

Is this the same thing that Cousteau's Calypso had at one time?

Alcyone, not Calypso. But yes, it would seem so.

 

[crescent]

Alcyone, not Calypso. But yes, it would seem so.

I get the impression from wikipedia that a rotor sail is different from a turbo sail (which is what the Alcyone has).

They look similar, but don't work the same way.

Rotor ship

My first thought was that this was some sort of ship-borne version of the Blackbird. Apparently not.

 

[Trebuchet]

Interesting! And now I have no idea how that land thing works. It sounds like it's chasing it's tail.

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