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Transportation Earth Science Technology

Spinning Metal Sails Could Slash Fuel Consumption, Emissions On Cargo Ships (sciencemag.org) 170

sciencehabit shares a report from Science Magazine: U.K. soccer star David Beckham was known for "bending" his free kicks over walls of defenders and around sprawling goal tenders, thanks to a physical force called the Magnus effect. Now, the physics behind such curving kicks is set to be used to propel ocean ships more efficiently. Early next year, a tanker vessel owned by Maersk, the Danish transportation conglomerate, and a passenger ship owned by Viking Line will be outfitted with spinning cylinders on their decks. Mounted vertically and up to 10 stories tall, these "rotor sails" could slash fuel consumption up to 10%, saving transportation companies hundreds of thousands of dollars and cutting soot-causing carbon emissions by thousands of tons per trip.

Rotor sails rely on a bit of aerodynamics known as the Magnus effect. In the 1850s, German physicist Heinrich Gustav Magnus noticed that when moving through air a spinning object such as a ball experiences a sideways force. The force comes about as follows. If the ball were not spinning, air would stream straight past it, creating a swirling wake that would stretch out directly behind the ball like the tail of a comet. The turning surface of a spinning ball, however, drags some air with it. The rotation deflects the wake so that it comes off the ball at an angle, closer to the side of the ball that's rotating into the oncoming air. Thanks to Isaac Newton's third law that every action must have an equal and opposite reaction, the deflected wake pushes the ball in the opposite direction, toward the side of the ball that's turning away from the oncoming air. Thus, the spinning ball gets a sideways shove.

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Spinning Metal Sails Could Slash Fuel Consumption, Emissions On Cargo Ships

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  • by thegreatbob ( 693104 ) on Thursday September 07, 2017 @08:26PM (#55156807) Journal
    ... it seems we have come full circle on ship propulsion technology.
    • by Anonymous Coward

      Or they could just use old fashioned sails and cut fuel consomption by 100%.

    • A quick google search shows many of these [interestin...eering.com]. Anything change or is this a publicity advert for David Beckham? Google images magnus effect ship.
      • A quick google search shows many of these

        Your link does not work, but yes rotor ships have been tried before. The Barbara of 1927 was probably the best known.

    • Sailing ships best ships

  • by CaptainDork ( 3678879 ) on Thursday September 07, 2017 @08:35PM (#55156831)

    ..."English," in tennis and pool.

  • Modern table tennis bats can impart a large amount of spin to the ball, causing it to drop quickly or float, depending on the direction of imparted spin.

    • of all the sports that employ this, why reference table tennis? :)

      baseball => curve ball
      tennis => drop shot
      i'm sure there are other examples, but TT is pretty niche (though fun)

      • of all the sports that employ this, why reference table tennis? :)

        baseball => curve ball tennis => drop shot i'm sure there are other examples, but TT is pretty niche (though fun)

        Perhaps because the effect is so dramatically noticeable in table tennis. Somewhat less so in tennis, and much less so in baseball.

        The purpose of the spin in the tennis drop shot isn't to generate a Magnus effect, which actually holds the ball aloft longer. The backwards spin on the ball is used to decrease the bounce forward and may even cause the ball to bounce backwards after hitting the ground. The Magnus effect is used in tennis in the serve and forehand topspin.

      • golf, backspin. the effect is more or less instantaneously visible in table tennis, also, due to the very low mass of the ball.
  • If the wind is always perpendicular to the way you want to travel. Of course the most reliable wind is from the ship moving forward thanks to its actual engines, which certainly isn't perpendicular to where you want to go. So now you have to apply a force to counter it to go in the direction you want to go.
    • Re:Great (Score:5, Informative)

      by nasch ( 598556 ) on Thursday September 07, 2017 @09:39PM (#55157011)

      Well if you read the article (ridiculous, I know)...

      Rotor sails are generally effective if the wind is moving faster than 18 kilometers per hour—roughly 10 knots—and is blowing across the ship’s bow at an angle of at least 20. Ships often encounter such conditions on northern Pacific and northern Atlantic shipping routes

      • Seems like a rotor sail could drive a generator collinear with the axis of rotation no matter what direction the wind comes from, then apply it directly to propulsion using electric drive.

        Worst case, the wind comes from the front, but instead of just being a counter-force, it contributes to forward motion to some degree.

        And of course, if there are lossy angles, you pull them down.

        Just speculating.

        • by jeremyp ( 130771 )

          The wind doesn't make the rotor sail spin more. In fact, thanks to the faster airflow and friction, it'll probably slow it down. All the spin comes from an electric motor, so it would be more efficient to just connect the electric motor directly to your generator. Then I guess you could supply the motor's electricity from the generator.

          Hmm, there ought to be a law against that...

          • by fyngyrz ( 762201 )

            The wind doesn't make the rotor sail spin more.

            Not what I was thinking, then. This is. [thegreenage.co.uk]

            Wind comes from any angle, it turns the shaft. The shaft turns a generator or alternator, and the resulting power gets fed to the screw(s.)

            A ship's mass gives a wind turbine a relatively fixed reference. So as long as there's wind, there's power generation.

            The process I describe turns wind energy in any direction into motive power in the desired direction.

        • This is exactly how that land sail vehicle "going downwind faster than the wind" works. It takes the angular for used in tacking and puts it to work as angular blades on a windmill, then attaches it to the wheels.

          The question here is how large must the sails (or bladez) be to get a noticable input of energy at that cargo ship scale, and how durable are they for long term use.

          • I'm not sure what you're saying, but in a sailboat sailing into the wind works because the sails, when filled with air, make good airfoils.

  • Not happening. (Score:2, Interesting)

    by Gravis Zero ( 934156 )

    saving transportation companies hundreds of thousands of dollars and cutting soot-causing carbon emissions by thousands of tons per trip.

    Ha! The engines are already terribly inefficient and they could easily be optimized a little and do both of these things. So why not do it? Simple, it has to always work because time is money. Besides, we would all be better off if we connected all six continent with a single intercontinental railroad. Not only would things arrive faster, it would be better for the environment.

    • Re:Not happening. (Score:5, Informative)

      by drinkypoo ( 153816 ) <martin.espinoza@gmail.com> on Thursday September 07, 2017 @09:41PM (#55157025) Homepage Journal

      Ha! The engines are already terribly inefficient and they could easily be optimized a little and do both of these things.

      Well, no. The most efficient internal combustion engines on the planet are in container ships. They are ultra-large, ultra-low RPM diesels, and they can reach around 50% efficiency.

    • Ah, I see. You had me going for a bit. I thought you were serious about thinking of something that no one else thought of in 150 years of burning oil to transport goods. That's cute. Though in the future you should end your post with [/sarcasm] so people don't think you've gone insane or something.

  • I seem to recall reading about this as a kid back in the 60s in Popular Science. It was supposed to make shipping freight cheaper. But for some reason it never caught on. Is this round 2, fifty years later?

    • I seem to recall reading about this as a kid back in the 60s in Popular Science. It was supposed to make shipping freight cheaper. But for some reason it never caught on. Is this round 2, fifty years later?

      According to the article the reason why it didn't catch on was the cost of running the engine to turn the sail. Modern material science allows them to be built out of lighter materials like carbon fiber, etc. They say that it takes about one-third the power to turn it, making it more efficient and the economics more viable.

      That being said, it still needs a steady 20+ knot wind blowing perpendicular to the line of travel so it wouldn't be useful for all shipping lanes, limiting it's current application. Pe

    • by nwf ( 25607 )

      I seem to recall reading about this as a kid back in the 60s in Popular Science. It was supposed to make shipping freight cheaper. But for some reason it never caught on. Is this round 2, fifty years later?

      And I recall reading it in the 80s in Popular Science. I'm sure we'll be reading about it in another 20 years.

    • I seem to recall reading about this as a kid back in the 60s in Popular Science. It was supposed to make shipping freight cheaper. But for some reason it never caught on. Is this round 2, fifty years later?

      I seem to recall reading about this as a kid back in the 60s in Popular Science. It was supposed to make shipping freight cheaper. But for some reason it never caught on. Is this round 2, fifty years later?

      I've read of this before, I gave it some 20 years ago. 60's sounds reasonable as it's such a simple a techonolgy. Popular Science does have a tendency of covering an new produce (what's new) that never makes it to the market/masses.

  • right up there (Score:2, Insightful)

    by doctorvo ( 5019381 )

    Rotor ships are right up there with Sterling engines, fuel cells, and a lot of other "great ideas" that turn out not to be so great in practice. When a fairly simple technology like this hasn't caught on for over a century, there's probably a good reason for it. My guess is in the case of rotor ships, it's higher purchase price, higher maintenance costs, higher weight, higher center of gravity, vulnerability to high winds, and insufficient savings under real weather conditions.

    • Re:right up there (Score:4, Informative)

      by nasch ( 598556 ) on Thursday September 07, 2017 @09:42PM (#55157027)

      Or you could actually read the article and see that it's because better materials, higher cost of fuel, and greater pressure on emissions are starting to make it an attractive proposition.

      • I read the article. Unlike you, who seems to uncritically swallow every b.s. the press presents you with, I actually thought about it too.

      • Maintenance (Score:5, Interesting)

        by Solandri ( 704621 ) on Friday September 08, 2017 @12:51AM (#55157389)
        I suspect maintenance costs are going to kill this idea. Ask anyone who owns a boat (power or sail) used in the ocean. You spend almost as much time maintaining it as you do using it, and replacing corroded parts is one of your biggest expenses. Even if they made the rotors out of a corrosion-resistant material like fiberglass, the fact that you need to rotate them means a lot of precision metal parts which are going to corrode and wear unless on a strict maintenance schedule. (Yes propellers spin, but they're fully submerged so you can use sacrificial anodes [wikipedia.org] to protect them from corrosion. Something up in the air with droplets of saltwater mist on it is going to corrode almost overnight.)

        It's the same problem the NS Savannah [wikipedia.org] encountered. Making it nuclear power dropped its fuel costs to near zero. But the increased labor required to operate and maintain the nuclear reactor ended up making it more expensive than a cargo ship powered with fuel oil.
        • by nasch ( 598556 )

          Surely they can figure out a way to have the bearings and such not exposed to salt water spray. Not to say they'll be zero maintenance, but that just seems like a solvable problem.

    • When a fairly simple technology like this hasn't caught on for over a century, there's probably a good reason for it.

      Just like fuel injection....

      • You don't see the difference between big, showy perpetually "almost ready" technologies like rotor sails, and invisible internal improvements like fuel injection? Seriously?

      • Mechanical fuel injection 'caught on' during WWII. For aircraft, basically as soon as it was feasible. EFI caught on as soon as it was feasible, for racing. 10 years later for emission control.

        • Mechanical fuel injection 'caught on' during WWII. For aircraft, basically as soon as it was feasible. EFI caught on as soon as it was feasible, for racing. 10 years later for emission control.

          And other technology that hasn't caught on for decades may also catch on once they become feasible too.
          To counter the GP's claim, just because something didn't catch on first time it was invented doesn't prevent it from catching on at some later stage when other external factors change.
          If there's a good reason why this won't work I'm happy to hear it, but saying it can't work purely because it was tried once ages ago and failed is a bit short sighted.

    • by Ocker3 ( 1232550 )
      If you RTFA, you'll notice that it is the materials used in the sails that have changed, making it efficient enough to be worthwhile. Ah, but this is /. how many RTFA??
    • When a fairly simple technology like this hasn't caught on for over a century, there's probably a good reason for it.

      Yes because we know everything right off the bat. There certainly hasn't been any advances in transport that has gained wide spread adoption over half a century after the discovery of the mode of transport. /Sarcasm

      For a practical example see Winglets. Invented in 1897, patented for aircraft use in 1930, didn't even get considered for passenger aircraft until the late 80s, and now because of the large fuel savings and stability you get for this over 100 year old invention you won't find a passenger aircraft

      • There are actually surprisingly many aircraft without winglets. For example neither of the two latest Russian airliners have winglets, even though USSR has been one of the early adopters. SAS still has a lot of their B737 flying with clean wings, B777 and B787 don't have winglets (they have raked wingtips instead). Clean wings have their benefits, so winglets are always a trade-off.

  • by bkmoore ( 1910118 ) on Thursday September 07, 2017 @09:27PM (#55156985)
    Gustav Magnus discovered what came to be known as the Magnus effect while studying why artillery projectiles would drift in the direction of spin.
    • And with a decent scope and light coming from the proper direction you can see it happen to a 22 bullet in flight. Just like artillery but on a smaller scale.

  • For a good visual example, watch the Veritasium video on the Magnus effect [youtube.com]. Not only does it explain the effect using a spinning basketball dropped off a dam, but it also has pictures of what these ships will look like with rotor sails.

  • by Bruce Perens ( 3872 ) <bruce@perens.com> on Thursday September 07, 2017 @10:20PM (#55157103) Homepage Journal
    See the Wikipedia page on Rotor Ship [wikipedia.org]. This is a 1920's invention, and a relatively large ship was built in 1926 and is documented in the German Wikipedia [wikipedia.org]. Even if you don't translate the page, the photo is clear.
  • OK, humor aside...We've all seen/experienced these effects in everything from pool to baseball, etc. but it is ALWAYS good to learn the "why" behind the "what".
  • by dilvish_the_damned ( 167205 ) on Thursday September 07, 2017 @10:51PM (#55157165) Journal

    Of topic but... "Spinning Metal Sails": I was looking for a name for my Styx cover band.

  • I wonder if it could be used for lift in aircraft design in place of traditional wings. It seems it would also apply to rotating cylinders instead of wings. I would guess that lift would be variable depending on the rate of rotation.
    • by Megol ( 3135005 )

      That - just as the idea of using this effect as sails - isn't a new idea. It have been tried. The result: how do the wings of current airplanes look like?

    • by jbengt ( 874751 )
      Traditional wings were traditionally modeled as creating a circulation [si.edu] or series of vortexes [wikipedia.org] around the wing imposed on the general airflow, just as if rotating cylinders were creating the lift.
      So, yes, the general aerodynamics of this is not much different than that of traditional wings, just the method of creating circulation.
  • The idea isn't new, the incredible claims aren't new and actually testing it isn't new either. What have changed since last time this was attempted and failed?

  • The wake behind a ball is NOT like the tail of a comet - the tail of a comet points (approximately*) away from the sun, not opposite to the direction of motion.

    Comet tails are not caused by some kind of drag - the comet moves in a vacuum in (almost**) geodesic motion around the host star.

    * Yes, there are actually two tails, dust and gas, directly not exactly away from the sun. The point is really that comet tails do not follow comets around the sun.

    ** M_comet/M_sun is normally pretty small, etc.

  • I vaguely remember looking into Magnus effect sails many years ago. I think the magazine Popular Science had an article on them that led me to do further reading on the subject.

    IIRC; There were some major mechanical engineering problems to be solved before the concept could be scaled up to the size needed for commercial shipping.

    1) Freakin' huge tubes, essentially only mounted at one end meant doing some serious engineering on the drive motors, bearings and so on, so as to not snap off in bad weather. On

  • In the 1850s, German physicist Heinrich Gustav Magnus noticed that when moving through air a spinning object such as a ball experiences a sideways force. The force comes about as follows....

    This has to be the most Slashdot way ever to explain something that everyone who has ever played a sport ever [wikipedia.org] needs no explanation for.

    Try not to maim yourself walking from your desk to bathroom today.

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