Flettner Rotor Sails Again?

Well folks, I must admit I’m a bit confused by this article:

It shows two (2) tilt-down flettner rotors on a ship, saying:
“The Norsepower rotor sail is the first third-party verified and commercially operational auxiliary wind propulsion technology for the global maritime industry.”

I was under the impression that this rotating-cylinder-sail concept had been shown to use more power than it produced in previous trials. We’ve covered the topic here quite a bit. The article does not mention the previous failures, but instead claims the system is a new idea, implying it is somehow proven, yet never before used. If it has never been used, how do they know it is effective? Did they check the previous attempts? The article does not mention such basic factors - welcome to the world of “press-release breakthroughs”. All presented as definite, yet only in a future-tense, of course. Well, at least they show a picture, and while not mentioning the basic fact that power is required to spin the rotors, let alone that the amount of power required to spin the rotors has so far amounted to more power than the rotating sails provide in return, the article implies this is all good, well-thought-out, and going to (in the future of course) save fuel…
Is this more delusion-on-steroids, or is the story accurate but just missing all the key points of relevance and significance to people like us who know it’s been tried before (and failed), and would like to know the details?

OK well, here’s the article that lead me to the flettner sail article:

It vaguely describes some sort of zero-fuel container ship(?) for shipping fertilizer around Norway, supposedly replacing trucks:

" The Yara Birkeland will transport mineral fertiliser between Porsgrunn and Brevik and will contribute to significant emission cuts during transport. This an excellent example of green transition in practice, and we hope this ship will be the start of a new type of emission-free container ships. There are a lot of places in the world with congested roads that will benefit from a high-tech solution like this,” said Mr Holsether."

Now I note they are using the term “green”, whereas I would correct that to “clean” since if you want “green”, then, according to NASA satellite data, producing CO2 is what has been greening the Earth for the past several decades.

Anyway, I was hoping for a picture of the ship, but am also a bit confused by the idea that a lot of trucks are being replaced by a ship in the first place. That, to me, is way more significant than exactly how the ship is powered, which they really do not say.

And then they get into promoting ammonia as fuel. As far as I know, the concept is a workaround to address the unworkable nonfunctionality of “hydrogen as energy storage”. The idea is, the energy density of hydrogen is so abysmally low that it is not even worth compressing to store it, because as “the gas laws” tell us, compressing any gas takes the same amount of energy per molecule, no matter how much energy each molecule contains, and with hydrogen having only two hydrogen atoms and no carbon atoms, it takes about half the energy it contains just to compress it into a small enough pressure tank to leave room for cargo. So instead of moving on, they are using a nitrogen atom to hold one more hydrogen atom, and the NH3 (ammonia) then holds (whoopee-doo) a paltry 50% more hydrogen than H2 alone. Then they can supposedly convert the ammonia back to hydrogen. Or just burn the ammonia! Known downsides include the extremely low energy density, difficulty igniting ammonia, production of unwanted combustion byproducts including various oxides of nitrogen which are very strong greenhouse gases, plus the extreme toxicity of ammonia gas - it will burn you and you can die from a leak. Anyone who has driven a natural gas powered vehicle is familiar with the very low power it delivers in an internal combustion engine. Ammonia is way worse - it does not want to burn. It really only works when mixed with hydrocarbon fuels, but then you have two fuels, 2 fuel systems, and all the hazards of a compressed tank of deadly ammonia gas onboard. What could possibly go wrong? Everything? I really think people are losing their minds. Facts just don’t matter anymore. There seems to be no limit to the absurdities at this point. Of course both of these news stories are set in the near future. As with AWE, it always seems to be “next year”, but somehow, “next year” never arrives - it is always “this year” no matter how many stories people can cook up about "next year, when it arrives, “next year” remains “this year”.

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I was not aware of ammonia, this is the first I learn of it besides the generic statements about using it as fuel. Thanks for todays «TIL» session.

The Yara Birkeland is a fully electric vessel that will transport «stuff» from a factory to another place. I dont know more details. But its an autonomous fully electric vessel, so thats interesting. It does not have flettner rotors or gas propulsion. The range is pretty short. But I believe there is not much wrong about this project from an environmental point of view. And the Norwegian government spent $15 mill to build it, so it better be good. Maybe its more a sign of the real costs of cutting CO2 emissions than anything else.

If you can already say that H2 and NH3 are not viable solutions for shipping, maybe you should get busy building wind based propulsion for ships, because it seems to me there are not many options left. I am pretty sure emissions will have to be cut at one point, leaving only wind and synthetic fuel and nuclear as options for propulsion. So that means drastically more expensive shipping and then probably distributing the worlds production of goods more evenly around the globe.

Anyways you seem well positioned to influence the «wind propulsion» part of the equation. I dont think the LCOE for this kind of power need to be very low, in a future without fossile fuels in shipping

So you’re saying that all the previous articles and papers claiming working breakthroughs for wind-powering ships, such as skysails etc. are wrong, I guess. That we’ve been reading fiction rather than fact. Good that somebody noticed. Back to fantasy vs reality. Which are we really interested in here?

Im only interested in things that could work, then in things that can actually be built :slight_smile:

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It not just in theory at this point

I saw this today by coincidence

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I think you can say theory, turned practice a long time ago.
The difference is? that many wouldn’t get the chance to build full scale. So the idea end up doing a loop. The old chestnut of where ideas go to die.
I wonder if they are good for energy production when anchored? I can’t say how many ships are out there like this? While my minds on? do you guys reckon? that the current three bladed turbines, could be retrofitted with a skin that does exactly this on the mast section?

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Photographic proof! :slight_smile: I wonder whether they were flettner rotors, as a start. If so, how much energy were they saving? I’m assuming there was an engine running too.
On the one hand, the concept can provide propulsion like a sail.
But on the other hand, last time around, what I remember was it used too much energy just to spin the cylinder than it was worth - like maybe even used more energy than it produced?
I’ve seen airplanes use spinning cylindrical wings, so that has been tried.
Seems like the results weren’t worth repeating, or we’d see more airplanes like that by now, right?
I’m not sure what’s changed since the last time flettner sails were tried, and given up on. What’s so bad about just regular sails?

Flettner sails are so easy to operate

Point taken, but what about all that power they supposedly use to spin? If a sail were reeled off a round mast, it would only need power during unfurling.
I’m still just wondering if they even make sense from an energy in/out standpoint? And it doesn’t seem like new ones could be that different from old ones - just a spinning cylinder… Either they are net energy producers or net users. And if they are producers is it enough to bother with? Does it even overcome the extra weight? Cost? Does the profile cause drag under engine power if winds are not favorable? Is that more total net drag than net propulsion over time? Why don;t we hear the full discussion? Why is it always favorable hype for the concept without discussing the tradeoffs?

You are right. This may not be a flettner rotor

Could be this one

Where is this vessel going?

The vessel departed from FARSUND, NO on 2022-09-03 18:38 LT (UTC +2) and is currently sailing at 13.6 knots with Northwest direction heading to IMMINGHAM, GB with reported Estimated > Time of Arrival at 2022-09-05 06:45 LT (UTC +2) local time (41 minutes ago)

Two of Norsepower’s largest 35m tall Rotor Sails were retrofitted onto Ro-Ro operating in the North Sea in January 2021. They are predicted to reduce emissions by an estimated 25%. The Rotor Sails onboard SC Connector are the world’s first tilting Rotor Sails enabling vessel to pass under bridges etc. With this installation SC Connector became Norway´s largest sailing roro vessel and one of the most powerful sailing ships ever built.

I find this somewhat impressive. Two sails each 175 square meter area seems to have come a far way already.

A quick estimate these provide 250 kN [25 ton force] traction force at lift coefficient 6 and 10 m/s wind speed.

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I had corresponded with the head of the technical department at Anemoi. He provided me with some very informative information, including the power consumption of the spinning motor as a function of the size of a Flettner rotor. As this information was given to me by private mail, I can’t make it public. However, I can provide it in private mode.

The rpm is mentioned in the pdf, and leads to a high peripheral speed (maximum about 48 m/s). Maximum Thrust Generated (kN): 120 to 385 kN (12 to 38.5 ton force) according to the size of the rotor.

In AWE field some advantages (and disadvantages) could occur: this has been discussed in the forum. But some further investigations could be made.

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Worth mentioning. Just watch out for how it steers of to the right with respect to spin.

Todays crazy idea. Is it really mostly efficient to rotate the whole magnus cylinder? why not just move the air at the point where it splits between left and right side of the magnus cylinder. Would not the effect be much the same? And the fans are working perpendicular to the non forced airflow… which seems good?

Anyway, not to be taken too seriously, this looks like a road leading to somewhere “Fanwing” or possibly to the original Flettner design…

(Fanwing-ish)

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I think this idea of a more or less cylindrical profile with fans has been investigated by Jacques-Yves Cousteau with the Alcyone on which two turbosails has been implemented. A Turbosail does not rotate.

It consists of an airfoil, vertical and grossly ovoidal tube, with a mobile flap which improves the separation between the intrados and extrados. An aspiration system pulls air into the tubes, and is used to increase the depression on one side of the sail; a reaction force occurs as the result of the pressure difference. In this way, the sails act as wings, creating both lift and drag.

A movable, flap-like trailing-edge shutter and a fan-drawn aspiration system are used for control and increase the magnitude of the maximum reaction force.

As a result of this design, the turbosail provides a reaction force, a component of which, thrust, is available for the direction of travel. Just like an unpowered sail, thrust cannot be obtained when making headway directly into a headwind, nor can it be obtained without wind. However, the use of fan-drawn aspiration, which requires engine power, increases the generated reaction force compared to the unpowered device.

http://www.thiiink.com/history-of-flettner-rotor/history-of-windpower/
image

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The turbosail would seem a real competitor to Flettner rotor for ships.

Also I think the Fanwing would score well on that chart.

Now there is a problem I think AI could solve; generate a optimum fan power use and wing shape…

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Nice chart, Pierre. I’d be curious to see a lift/drag chart like that.

Very interesting. This reminds me Co-Flow Jets.

I would also like to mention that a multi foil wing could give us lift coefficient of >3 without using any fans, so that seems like an improvement over a few of these.

Brings back this paper to mind, promising C_L of > 5 and still glide ratio > 10 [PDF] Drag power kite with very high lift coefficient | Semantic Scholar

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