The Flettner Rotor Sail
May 30, 2018 3:02 AM Subscribe
Invented over 100 years ago, this tubular sail may yet fulfill its promise. As pressure intensifies for the global shipping industry to decarbonise, Norsepower plans to bring back these fuel-saving mechanical sails to the decks of huge tankers that roam the seas today.
Was going to complain about no mentions of the Alcyone and her turbo voile, but I guess it is a different kind of sail.
posted by snofoam at 5:39 AM on May 30, 2018
posted by snofoam at 5:39 AM on May 30, 2018
Was also going to note that I was surprised to learn that Flettner rotors and turbosails* are totally different mechanisms for putting tall cylinders on your boat to make it go.
*TO THE EXTREEEEM
posted by GCU Sweet and Full of Grace at 5:49 AM on May 30, 2018
*TO THE EXTREEEEM
posted by GCU Sweet and Full of Grace at 5:49 AM on May 30, 2018
Really interesting article. Thanks for posting!
posted by yoga at 5:49 AM on May 30, 2018 [1 favorite]
posted by yoga at 5:49 AM on May 30, 2018 [1 favorite]
These are cool, but I have seen them touted as "the future of shipping" since at least the early '80s. It would be great if they got widely adopted.
posted by fimbulvetr at 6:38 AM on May 30, 2018
posted by fimbulvetr at 6:38 AM on May 30, 2018
These are a pretty clean way to get some sort of sail on a ship, but a cylinder is pretty bad aerodynamically(drag coefficient of 0.47 vs 0.04 for a streamlined body). I'm sure they've done the math and it's worth it, but going faster than dead down wind or even worse directly upwind this giant round pole is a huge disadvantage. I wonder if there are plans for a big airfoil-ish soft cover you could lift up when it's not spinning to reduce drag. Even two panels that open up on the backside to give a little bit of a tail ( there are a few semi trailers that have a fold out boat tail to do something similar) could make a huge difference if a ship has to deal with much upwind travel.
posted by TheJoven at 6:47 AM on May 30, 2018 [5 favorites]
posted by TheJoven at 6:47 AM on May 30, 2018 [5 favorites]
Glad the article mentioned E-Ship 1, Enercon's wind turbine transporter ship that was the first recent ship to use these. Like most things Enercon, it's entirely different from anything anyone has ever tried, because that's the way they roll.
posted by scruss at 7:04 AM on May 30, 2018
posted by scruss at 7:04 AM on May 30, 2018
I'm guessing controlling the speed of rotation allows them to control the vector of thrust, but I still don't understand how they could produce a useful thrust when heading into the wind (as opposed to tacking. I can't see a tanker doing a lot of tacking). You can't reef these things like you would a sail when you're running a true sailboat with a diesel auxiliary.
I wasn't able to find any more information out about details of operation in different circumstances.
posted by seanmpuckett at 7:18 AM on May 30, 2018
I wasn't able to find any more information out about details of operation in different circumstances.
posted by seanmpuckett at 7:18 AM on May 30, 2018
Here's a recent Forbes article about a success installing these on a smaller cargo ship. Cost recovery is estimated at five-to-ten years, which is pretty good at this level.
posted by seanmpuckett at 7:21 AM on May 30, 2018
posted by seanmpuckett at 7:21 AM on May 30, 2018
How does 400 tons of fuel yield 1200 tons of CO2?
posted by under_petticoat_rule at 7:28 AM on May 30, 2018
posted by under_petticoat_rule at 7:28 AM on May 30, 2018
The carbon starts in the fuel, the oxygen starts in the air.
posted by paper chromatographologist at 7:31 AM on May 30, 2018 [19 favorites]
posted by paper chromatographologist at 7:31 AM on May 30, 2018 [19 favorites]
Useful Wikipedia articles: Rotor ship, Magnus effect. The Magnus effect is the same thing that makes a tennis ball sink and allows some baseball pitches to bend. Folks even tried to use it for airplane lift.
Does this this produce more propulsion than if you used the wind to turn an electric generator and channeled the power to conventional underwater propellers?
posted by Nelson at 7:38 AM on May 30, 2018
Does this this produce more propulsion than if you used the wind to turn an electric generator and channeled the power to conventional underwater propellers?
posted by Nelson at 7:38 AM on May 30, 2018
If nothing else I'm sorta trying to picture how ridiculous a modern ship with tall sails would look. I suspect that's sort of the biggest advantage here - a moderate improvement in overall efficiency (even with the occasional moments of poor aero efficiency sailing directly up or downwind - it's a cargo ship, how aero are they to begin with?) without having to crew a couple dozen deckhands to reef sails and shit.
posted by Kyol at 7:52 AM on May 30, 2018
posted by Kyol at 7:52 AM on May 30, 2018
Does this this produce more propulsion than if you used the wind to turn an electric generator and channeled the power to conventional underwater propellers?
My understanding of the modern sail experiments is that the ships get their primary propulsion from traditional underwater screws, while the sails mainly function to increase efficiency.
posted by tobascodagama at 8:01 AM on May 30, 2018
My understanding of the modern sail experiments is that the ships get their primary propulsion from traditional underwater screws, while the sails mainly function to increase efficiency.
posted by tobascodagama at 8:01 AM on May 30, 2018
How does 400 tons of fuel yield 1200 tons of CO2?
To a decent first approximation, each atom of carbon in fuel oil is accompanied by two hydrogens. When the fuel is burned, the carbon atom combines with two oxygen atoms to make a molecule of CO2, and the two hydrogens combine with another to make a molecule of water.
The atomic weight of carbon is 12; hydrogen, 1; oxygen, 16. So burning each 12 + 1 + 1 = 14 masses of fuel makes 12 + 16 + 16 = 44 masses of CO2 and 1 + 1 + 16 = 18 masses of water. And to a decent first approximation, 44 / 14 = 3.
posted by flabdablet at 8:09 AM on May 30, 2018 [15 favorites]
To a decent first approximation, each atom of carbon in fuel oil is accompanied by two hydrogens. When the fuel is burned, the carbon atom combines with two oxygen atoms to make a molecule of CO2, and the two hydrogens combine with another to make a molecule of water.
The atomic weight of carbon is 12; hydrogen, 1; oxygen, 16. So burning each 12 + 1 + 1 = 14 masses of fuel makes 12 + 16 + 16 = 44 masses of CO2 and 1 + 1 + 16 = 18 masses of water. And to a decent first approximation, 44 / 14 = 3.
posted by flabdablet at 8:09 AM on May 30, 2018 [15 favorites]
I'm guessing controlling the speed of rotation allows them to control the vector of thrust, but I still don't understand how they could produce a useful thrust when heading into the wind (as opposed to tacking.
The force that’s generated is always perfectly to the direction of the wind flow. So the rotor is turned off when the point of sail (see helpful diagram) is too close to the wind (close hauled or into the wind) or too much away (at a broad reach or running downwind), since in those conditions, there would be little or no forward vector component remaining in the force.
It’s turned on only when the point of sail is in the sweet spot, between close hauled and beam reach. Then, there will be some component of the force vector in the forward direction, which the ship can use. It just has to set rudder, accordingly.
Incidentally, this illustrates another disadvantage of these kind of sails. While traditional sails are likewise “in irons” and cannot drive directly into the wind (they, too, prefer to sail close to the wind to take advantage of the airfoil effect*), the traditional sails ARE able to run downwind, because they can take advantage of large sails that catch the wind, rather than just relying on the airfoil effect.
*I’ve been a little lazy calling it the airfoil effect, since that’s the more familiar term. I suppose to be more precise, one should call it the Coanda Effect (as opposed to the common misconception — and one I also held for a long time — that airfoil dynamics are due to the “equal path time” aspect of the Bernoulli Principle).
posted by darkstar at 10:35 AM on May 30, 2018 [3 favorites]
The force that’s generated is always perfectly to the direction of the wind flow. So the rotor is turned off when the point of sail (see helpful diagram) is too close to the wind (close hauled or into the wind) or too much away (at a broad reach or running downwind), since in those conditions, there would be little or no forward vector component remaining in the force.
It’s turned on only when the point of sail is in the sweet spot, between close hauled and beam reach. Then, there will be some component of the force vector in the forward direction, which the ship can use. It just has to set rudder, accordingly.
Incidentally, this illustrates another disadvantage of these kind of sails. While traditional sails are likewise “in irons” and cannot drive directly into the wind (they, too, prefer to sail close to the wind to take advantage of the airfoil effect*), the traditional sails ARE able to run downwind, because they can take advantage of large sails that catch the wind, rather than just relying on the airfoil effect.
*I’ve been a little lazy calling it the airfoil effect, since that’s the more familiar term. I suppose to be more precise, one should call it the Coanda Effect (as opposed to the common misconception — and one I also held for a long time — that airfoil dynamics are due to the “equal path time” aspect of the Bernoulli Principle).
posted by darkstar at 10:35 AM on May 30, 2018 [3 favorites]
This is fascinating. The entire "put a big spinning tube on top and in certain directions the ship will move faster" is so wholly unintuitive to me, that I love reading about it.
But also, all the talk of beam reaches and such reminds me that I would die rapidly as a sailor.
posted by Abehammerb Lincoln at 10:49 AM on May 30, 2018 [1 favorite]
But also, all the talk of beam reaches and such reminds me that I would die rapidly as a sailor.
posted by Abehammerb Lincoln at 10:49 AM on May 30, 2018 [1 favorite]
Aargh — that should have read:
“The force that’s generated is always perpendicular to the direction of the wind flow.”
posted by darkstar at 11:02 AM on May 30, 2018
“The force that’s generated is always perpendicular to the direction of the wind flow.”
posted by darkstar at 11:02 AM on May 30, 2018
About 10 or 15 years ago there was a proposal to put parachute-like retractable sails on big cargo ships, to be used only when heading downwind. They have the advantage of packing up into a very small space and being easy to install and deploy. I think the idea was a computer would tell you when it was advantageous to deploy it based on the wind direction and ship's course.
Never heard what happened to them; certainly haven't seen any in use, although I suppose in inland waters you never would.
posted by Kadin2048 at 11:12 AM on May 30, 2018 [3 favorites]
Never heard what happened to them; certainly haven't seen any in use, although I suppose in inland waters you never would.
posted by Kadin2048 at 11:12 AM on May 30, 2018 [3 favorites]
After more Googling than it should have taken given the name, I found the parachute sail people. They're called SkySails and apparently they are still around. Technically it is a very large, inflatable kite.
There are some interesting details on that page about the problems inherent in getting green technology adopted by shipping companies:
posted by Kadin2048 at 12:03 PM on May 30, 2018 [3 favorites]
There are some interesting details on that page about the problems inherent in getting green technology adopted by shipping companies:
There’s a structural problem slowing down the process: ship owners (who have to make the investment) often don’t pay for the fuel – that’s the charterer’s duty. The charterer on the other side doesn’t charter the ship for long enough a period to make low-carbon technologies pay back.
Fuel costs mostly get passed onto the shipper so we see little use in installing potentially expensive, untested technology to which we see no other benefit. Basically I am interested but will not be the first to try it on a large scale.Those issues seem to apply even more strongly to the Flettner system, which can't just be tacked on to an existing conventional ship. I'd guess that's why you need to look at ships that are not usually under charter for early adopters.
posted by Kadin2048 at 12:03 PM on May 30, 2018 [3 favorites]
Here's some video of the Viking Grace underway with the rotating (and sometimes non-rotating) sail.
posted by flug at 1:26 PM on May 30, 2018 [1 favorite]
posted by flug at 1:26 PM on May 30, 2018 [1 favorite]
I really wonder how this giant cylinder structure holds up in the kind of storm that ships encounter at sea. The reason that sail boats -- aside from world speed record and certain racing scenarios -- stick with fabric sails even though wing sails are more efficient is that fabric sails can be reefed and taken down in heavy weather, leaving only the mast and standing rigging. Even so, masts and standing rigging are sometimes damaged in severe weather. These ships will always have these huge, ungainly cylinders getting blasted by the wind, whether in port or in the path of a hurricane. Maybe this is why the first application is a ferry?
posted by chrchr at 2:48 PM on May 30, 2018 [3 favorites]
posted by chrchr at 2:48 PM on May 30, 2018 [3 favorites]
Future sailors: what will ships look like in 30 years? Includes the tubular sail, but also others.
posted by rory at 2:43 AM on May 31, 2018 [1 favorite]
posted by rory at 2:43 AM on May 31, 2018 [1 favorite]
I'm guessing controlling the speed of rotation allows them to control the vector of thrust
The force that’s generated is always perfectly to the direction of the wind flow.
The force due to the Magnus effect is perfectly perpendicular to the wind direction. But the net force on the rotor will be the vector sum of the Magnus effect force and a straightforward drag component parallel to the wind direction. And since the magnitude of the Magnus effect component does depend on the rotor's rotational speed with respect to the wind, the direction of the net force has to depend to some extent on that rotational speed.
but I still don't understand how they could produce a useful thrust when heading into the wind (as opposed to tacking. I can't see a tanker doing a lot of tacking).
Just as for a conventional sail, there will be a range of wind angles that are too much opposed to the direction the vessel wants to go to allow the sail to work. Presumably a Flettner-rotor tanker could tack in order to make way upwind, but given that the rotor is responsible for a fairly small percentage of the total drive power, it would probably be rare to find conditions where doing so results in fuel and/or time savings.
posted by flabdablet at 6:58 AM on May 31, 2018 [1 favorite]
The force that’s generated is always perfectly to the direction of the wind flow.
The force due to the Magnus effect is perfectly perpendicular to the wind direction. But the net force on the rotor will be the vector sum of the Magnus effect force and a straightforward drag component parallel to the wind direction. And since the magnitude of the Magnus effect component does depend on the rotor's rotational speed with respect to the wind, the direction of the net force has to depend to some extent on that rotational speed.
but I still don't understand how they could produce a useful thrust when heading into the wind (as opposed to tacking. I can't see a tanker doing a lot of tacking).
Just as for a conventional sail, there will be a range of wind angles that are too much opposed to the direction the vessel wants to go to allow the sail to work. Presumably a Flettner-rotor tanker could tack in order to make way upwind, but given that the rotor is responsible for a fairly small percentage of the total drive power, it would probably be rare to find conditions where doing so results in fuel and/or time savings.
posted by flabdablet at 6:58 AM on May 31, 2018 [1 favorite]
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It’s the same effect that gives a topspinning curveball in baseball its unexpected downward movement (greater than that expected by gravity).
The non-spinning cousin to this is the airfoil effect, which is what airplanes use to provide the lift force in the direction of the upper side of their wings.
posted by darkstar at 3:25 AM on May 30, 2018 [8 favorites]