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Spinning Metal Sails Could Slash Fuel Consumption, Emissions On Cargo Ships (sciencemag.org)
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.
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.
What you want is mostly in the article.
“Our largest rotor sails can provide forward thrust equivalent of up to 3 megawatts of main-engine power while drawing less than 90 kilowatts of electricity,” Riski says.
The Emma Maersk, a recently launched cargo ship, boasts 111 MW of propulsion. It's likely that these rotary sails are indeed more efficient than an underwater propeller but unable to deliver the same power as an underwater propeller without covering the deck in rotary sails. Having a few to lower fuel costs of the less efficient underwater propeller is simply economical. If it's actually economical, you'll see it on more and more ships just like those little winglets on airplanes.
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.
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Oil is not expensive enough. It's just a matter of time.
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You again with your half knowledge. Nuclear marine propulsion is so horribly expensive only a few navies can afford to operate that. There has been only handful of merchant ship with a nuclear reactor, and only two of them actually ever carried cargo. You see, marine reactor fuel is highly enriched, which is very expensive, and the reactor life span is ridiculously short compared to a marine diesel. After decomissioning the whole reactor together with the coolant loop have to be cut out and buried somewhere - recycling is not possible. The daily operating expenses for the Sevmorput is around 90k USD. A conventional freighter with a similar capacity has only a third of these daily costs and is permitted to any port.
"It's such a fine line between stupid and clever" -- David St. Hubbins, Spinal Tap
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 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 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.
Nuclear marine propulsion is so horribly expensive only a few navies can afford to operate that.
It is now. What happens to the price of nuclear propulsion when the oil runs out? People want their fresh bananas and coffee, and if it means using nuclear power then it's going to happen. Shipping by oil fired ships used to be real expensive at one time too. People figured out how to make it cheap. There's nothing that makes nuclear power inherently "horribly expensive". It's expensive now because there's probably only one or two such reactors built every year. If built one or two per month on an assembly line, like we do with jetliners, then they get cheaper. Not "cheap" because anything that size is expensive.
You see, marine reactor fuel is highly enriched, which is very expensive, and the reactor life span is ridiculously short compared to a marine diesel.
The US Navy uses highly enriched fuel in their reactors because they need to operate their reactors in ways that a civilian ship doesn't. Highly enriched fuel solves a lot of problems that a low enriched fuel doesn't have. One problem highly enriched fuel solves is the production of xenon if output power is increased quickly, which is easy to solve in a commercial shipping environment, just don't stomp on the accelerator. If some idiot does get a lead foot then they'll just have to sit still for a few hours for the xenon to decay away.
The daily operating expenses for the Sevmorput is around 90k USD. A conventional freighter with a similar capacity has only a third of these daily costs and is permitted to any port.
It costs only three times as much to operate? Well then, all we need to see for civilian marine nuclear propulsion to be viable is oil prices to triple. The problem on costs isn't nearly as bad as I thought. We'll see civilian nuclear powered container ships in no time then.
Oh, and being unable to put a nuclear powered ship in a port is real easy to solve if it's carrying coffee and iPhones. That's a political problem, and those can be solved in a single election.
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It isn't. Even biodiesel and GTL is much cheaper than nuclear propulsion so if oil becomes too expensive, synthetic fuels and biofuels will be used. Nobody wants to pay for civilian nuclear marine propulsion except Russia, and they need it for the Arctic region.
They weren't. Just somewhat more complicated to build than steam turbine ships that used coal.
There is a lot of things that makes nuclear power inherently horribly expensive. First, everything has to be radiation-hardened because neutron flux damages pretty much every material. Second, the manufacturing tolerances have to be much lower. Average manufacturing quality won't do because subsequent repair is difficult to impossible. Third, for marine propulsion the fuel has to be highly enriched. People have been trying for over 60 years to make marine nuclear propulsion cheaper. Didn't work out and never will. We'll have fusion power sooner than that.
Nope, the main reason why all marine reactors - and not just the US navy - use highly enriched fuel is the power density. Even the four merchant ships with nuclear propulsion I have mentioned previously used highly enriched fuel and so do all the Russian nuclear ice breakers. There is simply no room on a ship for a reactor that uses 2-4% enriched fuel - they would be seriously huge.
You seriously think that fuel is the only operational expense on a ship? It isn't, that's why you won't see nuclear powered container ships ever. The operating cost on Sevmorput is triple of the operating cost of a conventional freighter with a similar capacity, which is about the lower end as container ships go. Large container ships are still about half as expensive to operate as a nuclear power ship, but can easily carry 20x more stuff.
That ships already carried cargo - well, two of them did - and yet they weren't allowed to many ports. This cannot be solved in a single election because maritime law is involved, and that is international.
"It's such a fine line between stupid and clever" -- David St. Hubbins, Spinal Tap