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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.
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
That being said, it still needs a steady 20+ knot wind blowing perpendicular to the line of travel....
That statement contradicts the article:
"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..."
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.
"You're right," Fisheye says. "I should have set it on 'whip' or 'chop.'"
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.
They don't really use "oil" on cargo ships, its more like asphalt tar. Since the oceans don't have any governmental bodies setting emissions standards, shippers are free to use the nastiest, foulest leftovers of distillation in their power plants. That crap'll be on the market decades, if not centuries, after the last of the light sweet crude runs out.
You're not competing against expensive "clean" fuel here. You're competing against the cheapest crap that'll burn.
I realize that ships burn bunker fuel, but even that is made from crude and subject to price changes in proportion to crude oil prices. While we're not talking a jump from $1 to $3 a gallon, a 10 cent to 30 cent spike makes a big difference to a shipping company. And while oil prices will fluctuate with the market we keep adding people to this planet and we keep growing economies and energy demand - oil prices will invariably rise over time. One day wind propulsion might make a real comeback.
Seven puppies were harmed during the making of this post.
There has long been talk of building modern windjammers, but it never happens.
There are reasons it doesn't happen, such as:
1. Bridges
2. Container cranes
3. Fixed port schedules
Kite sails avoid these problems, catch faster wind at higher altitude, and have the further advantage of already being commercially deployed.
It's going to be different from how you expect. I did the numbers once, and it came out something like less fuel is expended shipping white goods from the China shore to the UK shore than is spent delivering the white goods from the warehouse to your home. It was a factor of 3 IIRC. In other words, the delivery infrastructure will move to all electric long before we stop shipping things by sea in oil fuelled ships.
Those things are outrageously efficient. Even the engines themselves reach raw efficiencies of over 50%. By comparison the best full sized utility scale combined cycle plants manage 60 and normal coal fired powerstations are around 40 or so. And then they go slowly. And carry crazy huge amounts.
SJW n. One who posts facts.
What are they made of,
Steel.
as materials normally limit efficiency of the Otto cycle to 35%.
They're supercharged two stroke diesels, not otto cycle engines.
SJW n. One who posts facts.
There's increasing talk of regulating the fuel. Ships are already required to burn cleaner fuel near coastlines in a lot of places and some have been caught not doing this. I wouldn't be surprised if the end result is a requirement that any ships going to or from a nation's ports or travelling through its territorial waters must only burn cleaner fuel, because that would be a lot easier to enforce. That gives a big incentive to switch to more efficient propulsion.
There have been a few designs in recent years for ships with electric drivetrains, large solar arrays and wind turbines, and backup diesel generators (or primary diesel generators that are only expected to provide 50-90% of the total power depending on conditions).
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There's increasing talk of regulating the fuel.
There's no "talk" on the fuel side of the regulation. There's actual action which refineries are already gearing up to support. One big one is by 2020 there needs to be a 3% reduction in sulfur in open oceans (down to 0.5%). The last change happened only in 2015 where controlled area sulfur was reduced by 0.9% down to 0.1%.
There is talk on the burning of it side though with the actual emissions not being regulated yet. It's much easier to regulate what goes in the tank than what comes out of the exhaust in the middle of the ocean.