Maersk installed 100-foot-tall rotating sails on one of its tankers | Hacker News Reader

Maersk installed 100-foot-tall rotating sails on one of its tankers

wsj.com

389 pointspetethomas224 comments

Some years ago I read The Box by Marc Levinson, a history of containerized shipping. Highly recommend it. If you live in SF and have wondered about the numerous barely used piers, this book explains their history as well - and why the major container terminal ended up in Oakland instead.

One of the painful early lessons for the industry was the discovery that minimizing operational costs (particularly fuel and maintenance) trumps every other value. A pioneering containerized shipping company went bankrupt pursuing a high-speed shipping strategy that cost marginally more than low-speed competition.

Edit: Oh, there is a second edition! Updated link.

Edit: replaced unhelpful snark.

https://www.amazon.com/gp/aw/d/0691170819/

You might enjoy "Containers", an eight episode podcast about the shipping industry too. https://medium.com/containers

Two non-technology related containers story on the front page of hacker news, and they're both actually really interesting! Happy Friday!

Hey sails are technology. Just, really old technology.

And these "sails" are much newer tech...

and containers themselves are pretty new technology

Hmm... I've seen a couple shipping related stories, but nothing container related.

This one is about tankers, and the other was about bulk carriers.

Ignorant question: if operational costs trump all, especially fuel (Maersk says in the article 60% of operational cost) why not pure sail power? Is there some other maintenance cost or infeasability there? Or is there another hidden variable that is not satisfied?

unpredictability of wind, i'd imagine.

That and storms. You need engines to ride out or (better) avoid storms at sea.

Is a ship that big bothered by anything less than a hurricane?

I would think so, certainly of you add masts and sails that can propel that big a ship.

Example without sails: https://en.wikipedia.org/wiki/MSC_Napoli:

”during European windstorm Kyrill, severe gale-force winds and huge waves caused serious damage to Napoli's hull, including a crack in one side and a flooded engine room

[…]

the earlier grounding in 2001 did not contribute to the loss”

That ship was 62,000 tons. That’s not huge by today’s standards, but not small either.

When the Cutty Sark was the state of the art in merchant shipping, the steam ship was becoming a thing. The steam ship was much slower than the Cutty Sark and needed its own fuel to operate. It's a good example how the numbers alone don't necessarily add up for new technology.

This is a good question, and almost pure sail power may become a thing in the future. It looks like Maersk is trying to get ahead of the switch to cleaner fuel coming in 2020, which will increase their fuel costs by about 60%. This idea of putting sails on a large ship was at best only marginally cost-effective before now.

Some practical considerations come into play - while saving money is good, being able to reach your destination when you say you will is also worth something. With pure wind you lose that control. Deck size is not infinite, so there is a limit to how many sail towers are useful. Tower height also has practical limits before it destabilizes the ship. Handling bad weather is much easier with the on-demand power that comes from engines.

Why not use electrical propulsion and charge batteries from wind and solar? At first, as a fuel saving measure in optimal conditions (rely on internal combustion engines most of the time). Seems better than pure sail power, even though that is more efficient (due to direct wind to motion conversion).

Re:solar - there was an experiment where they covered a whole tanker with solar panels. During the day, they provided 10% of power....needed to run the lights on the ship.

Solar is just nowhere near good enough compared to the needs of a massive ship like this.

Wind would maybe work, but then remember that a turbine would effectively slow you down as you'd be pushing against the air.

At perhaps 100 watts per square meter, a Maersk triple E ("An arbitrary large ship") at approximately 400 meters * 60 meters would generate 2.4 megawatts peak, or perhaps 400 kilowatts averaged.

This is not nothing. It's roughly as much power as a redlined sports car engine. It might be sufficient to fight the worst ocean currents, since propulsion power scales so frighteningly faster than speed.

https://www.maritime-executive.com/editorials/the-future-ult...

It would also make sense, with larger ships, to just implement the nuclear tech we already have.

> This is not nothing. It's roughly as much power as a redlined sports car engine.

And a sports car is what, 3,000 pounds? A container ship is something like 200,000 tons. I guess they can power a redlining sports car engine when out to sea but not a whole lot else.

It doesn't take an enormous amount of power to move a big ship very very slowly; Froude's law, the first approximation of the relationship, scales power requirements with velocity squared.

A Maersk Triple E has two up-to-30MW-each engines and a design speed of 19 knots. You'd scale down speed by a factor of 12 to achieve 1.6 knots (0.8m/s), and out of that you would get to scale down power by a factor of 144 to meet your ~400kw solar power endowment.

The question is whether you can cross the most powerful currents, and at 1.6 knots you would certainly need to be cognizant of them to stand a chance, but you could ford them in the manner of fording a river: Get pushed downstream a bit, but cross the highest velocity area perpendicular.

http://www.aoml.noaa.gov/phod/gdp/images/climatology.jpg

The Maersk Triple E and huge bulk carriers are practically worst-case-scenarios for solar, because there's so much ship to displace water under every square meter of solar. A smaller lighter catamaran is likely to find itself with dramatically higher speeds, albeit not linearly higher with hull depth, since a longer waterline is more efficient.

I'm not suggesting this is practical. I think massive nuclear powered cargo ships capable of high speed is a hell of a lot more practical in a post-carbon world. But again: it's not nothing.

> nuclear ships

IANA(nuclear scientist) but I imagine that it has to do with the lack of nuclear engines available for the commercial market, which is due to nuclear technology being restricted by export controls and the like. Keeping nuclear engines and fuel out of the hands of others is much simpler when they're only on military ships with armories and soldiers, basically impossible on unarmed, undefended commerical shipping vessels.

Do correct me if I'm wrong ...

Wind is also extreemly limited. As a ship scales up there is proportionaly much less wind energy to work with. Cargo ships move as fast as windsurfers (25+mph). Think of a windsurfer's sail to hull ratio. And the ship isnt on a plane, but pushes through the water. I see 1000' tall mast(s), with sails the size of small towns.

A big cargo ship's engine can be 25000kw. The biggest wind turbines (750') generate about 8000kw. So.. three of them? The ship would need to be 1500 feet long just to make room. But the wind isnt constant. Five turbines? Bridges might be an issue.

>As a ship scales up there is proportionaly much less wind energy to work with.

It's the square-cube law in operation. It also applies to solar. The only application of solar mounted on a transportation vehicle that makes any sense is those ultra-light unmanned planes that cruise above 60,000 feet.

Solar panels on cars make sense. They may not provide much actual charging, but they can prevent discharge over time.

I meant in the sense of providing the power for the motor.

The solar doesn't necessarily have to be ON the ship. If photovoltaics continue their process of price drop in STC $/W ratio, or if at some point very high efficiency low cost nuclear becomes economical, it will be possible to crack hydrogen from sea water at a shore based facility and compress it into tanks. Then use that to power massive fuel cells on ships with fully electric azipod drives.

If your $ per kWh is something ridiculously low like $0.002 you can economically electrolyze h2o to pure hydrogen.

The surface area of the ship, don't care about that. A 20x20km area of the Mojave desert covered in super low cost PV can provide the power needed.

This is the same economy of scale thing as a solar powered car. If you were to theoretically cover every square cm of a Tesla model S in high efficiency PV, and let it sit in the sun all day, it might take a week or more to collect the 95kWh needed to charge it fully. But if the PV is somewhere else on rooftops or otherwise-useless arid land, connected to the grid, you can plug your car in to a 240V 30A socket in your garage and charge it every day.

I'm not an expert in this topic - I've just read a few books and shipping was covered in a few of my upper division classes.

They are the most important factors in the context of reliably shipping goods from port to port. If there was a sail technology that allowed reliable transit, predictable speeds and times (really slow is OK, a little late is not), and didn't cause an increase in other costs (say, insurance or maintenance), and could move the tonnage involved (up to 40 tons per container multiplied by thousands of containers, or enormous dry goods loads), I suspect it would capture a sizable portion of the market.

Edit: it occurs to me that significantly reducing fuel costs would allow entirely new kinds of loads to be transported and potentially radically alter the world economy. I once saw a chart where the Y axis was price per unit and the X axis was unit density. There was a line on the chart, above which it is economical to ship a good, below which it is not. The top right of the chart had things like electronics - which have been shipped since the dawn of the industry. The bottom left had things unprocessed ore, which have never made sense to ship.

> The bottom left had things unprocessed ore, which have never made sense to ship.

China mines and ships bauxite from Fiji to China.

https://aluminiuminsider.com/bound-chinese-shores-fiji-ships...

Without knowing much of anything: Bauxite is a bit special in that aluminum processing is extremely energy intensive, and I think the ore is often shipped to places with low electricity prices.

It is one of the bigger industries in Iceland: https://www.nytimes.com/2017/07/01/us/politics/american-comp...

I've long imagined some fun possibilities for this.

I picture a small-ish shipping ship, say something moving 20 or 30 containers only, fully autonomous (100% crewless) with sails and solar only powering it. Solar electric motors handling the near-land operations and "not enough wind" conditions, sails otherwise. If you had autonomous loading and unloading, you would have zero variable/operational cost.

I am certain there are very good reasons this would never work, but I still love the idea.

No hostages for pirates to take either (though I guess they could help themselves to all of the goods on the ship)

And the ships. Drop an anchor and demand ransom to cut it free.

Even easier, just spoof the GPS signals with your own higher powered broadcast and make the ship think it's sailing around while it's actually stationary. Cant find the link but, some university actually demoed this working in real life with an actual container ship.

Im imagining an LED throwie type big magnetic thing with gps RX and TX, and a satellite uplink. Cruise by the autonomous ship on a jetski near a port, thrown the magnet thing on, jetski away, disrupt from afar once the boat is out at sea.

Ye old compass and lag wont get fooled by such mischievous act.

Electromagnet.

Another fun possibility: a train of such ships connected by cables, which wind and unwind generators as the distances between them change, to power propulsion.

As for very good reasons why this would never work, sometimes that is beside the point. I am not in the running to redesign trade and power on my own terms, but sometimes I can flush out assumptions that don't need to be held.

The reason autonomous/crewless isn't really feasible or worth investing in is that most container ships only have a crew of about a dozen, and they are generally from low-wage countries so that their salary costs are far out-weighted by the fuel.

I think this is a good example where automation doesn’t mean getting rid of all jobs, just 99% (which has nearly the same effect). I mean, we still have blacksmiths hand forging swords ffs.

Maybe a little bit picky, but the average size of a crew on a, say, 9000 TEU container ship is actually closer to two dozen. 20-24 most of the time.

The number can rise further with more complex cargo.

Unless someone has spent time at sea they cannot appreciate all the maintenance a large ship requires. Crewless ships are pipe dream. But captainless ships, ships operated without officers to navigate them, are a real option. You keep the tiny crew for fixing things but the operation of the ship is handled from afar.

Crews are cheap. Ships' masters are not.

Alternatively, the repair crew don't stay on the ship. Have a mobile team on a faster boat going ship to ship rescuing and repairing ones that can't make it to port again.

Maintenance is not repairs. The work needed to prevent repairs has to happen ever day. A crew at sea doesnt sit around waiting for an alarm. They are tending to equipment, verifying sensors ... even touching up paint is an essential daily task.

Interesting perspective. I hadn't considered that.

Part of me starts to wonder now about building boats that are more resilient, but then I remember that salt water is terrible and surely by now someone would have if it were possible, since we spend so much money on humans doing that maintenance!

If man can build it, the sea will destroy it.

Spoken like a true sailor :)

If you've ever been on a cruise, you'll notice the "crew" (not the staff) constantly painting and maintaining -- even on a brand new ship. If you ask, they'll tell you that they have to constantly work on the upkeep because of the size of the ship (kind of like painting the golden gate bridge, once you're done it's time to start over again).

Funny, I had this idea around my head for a while tagged under the "world changing startups I'd like to try someday" :)

I think it will do to shipping what two engine, midsized passenger jets (A350/787) are doing to air travel: connect directly between small ports anywhere, instead of using very large ports as hubs. FedEx/UPS could have sea terminals anywhere, possibly automated.

Global shipping will only grow and I don't see a driver for air freight prices to drop enough so that things are truly international (e.g. buy a fridge from AliExpress).

I think it needs to happen, and will happen.

Slow is OK, but it must be exactly predictable. Don't be early, don't be late.

So you can use sails to help, but if you rely on them you might be late.

You can keep the timetable no matter what -- use sails just to save fuel consumption when weather is favorable.

I wonder: do sails alone generate enough power to move today's massive container ships? Or would the ships need to be smaller?

There's no question sails can move today's cargo volume. But the shape of the ships doesn't lend itself to sail power. I think these sails are specific to supporting other power. And the shape of today's ships is very much towards fitting more cargo. I think you'd need at least slightly bigger ships that are efficient for sail power alone, and able to carry similar cargo volume or mass.

I think such rotating sails could be almost called 'solid state' - basically zero hassle compared to a traditional canvas where there is always person on lookout, trim before wind picked up, make sure rigging is maintained, etc. That said these probably produce way less power.

Rotating sails and wind turbines have historically been extremely high maintenance due to the forces the long moment arm puts on the rotational coupling at the base.

I read an article about the potential of drone ships that claimed one reason ships don't go even slower is the logistics around having a crew on the ship for the entire voyage.

Capital expenditures are also pretty important. If the ships cost twice as much to build, you're paying twice as much in interest (or more). At the same amount of investment, you're shipping fewer things more profitably, and that only really makes sense if you can get attractive debt terms under pretty intense price pressure.

Fun trivia: when windjammers were going out of style, some businessmen still bought them for the low cost.

https://en.wikipedia.org/wiki/Gustaf_Erikson

For a while in 1930's small Åland had the largest sailing fleet in the world.

I'll second this, The Box is fantastic. It sounds like a dry subject, but Levinson did a fantastic job of telling the story of how containerized shipping changed the world.

Working in the industry this is only partially true. All liners have aggressively cut operational costs over the last years (esp. by scaling their operations, ordering bigger ships, reducing sailing speeds). Still, the industry is by and large value destroying. So, while the prevalent strategies might have prevented worse, they certainly didn’t turn around the industry.

Edit: It is even likely that the chase of lower operational cost played a major role in the current oversupply of capacity (thanks to a glut of mega sized ships)

Second the recommendation. Great book!

...why the major container terminal ended up in Oakland instead.

Whatever the reason, I'm sure everyone who uses a bridge in SF is happy about this.

The reason is that it was much easier to terminate the transcontinental railroad on the eastern shore of the bay. Not unrelated to your point.

> One of the painful early lessons for the industry was the discovery that minimizing operational costs (particularly fuel and maintenance) trumps every other value. A pioneering containerized shipping company went bankrupt pursuing a high-speed shipping strategy that cost marginally more than low-speed competition.

I’m not convinced that this is static — as far as I can see it should depend on the prevailing rate of interest. The more a company pays in interest on a loan, the faster it should want to realize its investment (which doesn’t happen by goods sitting in a container).

I’m not sure what the equilibrium interest rate is, exactly, but at some level of interest it should become cheaper to ship the goods faster, since you will save more in interest payments than the extra you pay for shipping (due to your investment becoming operational sooner, allowing you to pay back the loan).

It's called the Flettner rotor, it uses the Magnus Effect. Cool stuff but not exactly new tech. It gives a nice read, here's some links to wikipedia on the topic: https://en.wikipedia.org/wiki/Magnus_effect and https://en.wikipedia.org/wiki/Rotor_ship

I'm curious of what will be the results.

Apparently this is a turbo sail and not the same as the Flettner rotor. The Wikipedia article you linked to mentions the same. Ones powered by electricity and one by air? Both seem to take advantage of the Magnus effect though

https://www.google.com/amp/s/amp.theguardian.com/environment...

It’s not a turbosail. Turbo sails don’t rotate..

Ah, looks like you're right! I got confused by its mention in the article.

They claim 7-10% reduction in fuel usage, with fuel making up 60% of their total costs.

Given that they soon expect to be spending $5 billion/year on fuel for 800 ships, fuel spend is a bit north of $6 million/year for an "average" ship. But size seems to vary widely (they note that only the 80 of their largest ships are being considered for these sails).

At an installation cost of $2 million, saving 10% of an "average" ship would return 600k per year, or a 3.5 year paypack, which seems well worth doing where possible. And they'll obviously get better than that on their 80 largest.

Not a magic bullet by any means, but certainly seems worth using.

As long as they are reliable and have non-crazy maintenance costs it should be profitable now. I imagine some time and competition could cut that install cost in half too.

Economies of scale too.

I think that's something we lose sight of in software sometimes, where we're used to some token effort improving performance by 10x or more. In the real world, if you can make something 10% more efficient, that's a game changing, industry conquering advantage.

Too true. Like the new dodge ram etorque, using its electric motor to replace the alternator, it can launch the truck and let the combustion motor take over at highway speeds. 1-2 mpg is a large improvement for a truck. 1500 dollar option that pays for itself, and a good step towards getting battery tech into trucks.

I've seen it mentioned boats/ships using electric assist will also be another catalyst for battery tech integration, fuel costs on those large ships are always a topic.

Bolt on solutions that are affordable with quick turn around on investment.

Agree, but with a few caveats:

- The cost needs to be fairly easy to measure

- Some degree of competition in the industry exists (otherwise the capital could be used to increase revenue or acquire small potential rivals before they're too large to afford, among other higher return places to spend the capital)

- The industry is mature and sources of larger savings already exhausted

- Prospect for some future much bigger savings small (or at least not in conflict with the current effort)

- Prospect for the industry as a whole very good (in a shrinking market, 10% savings becomes lower priority than selling off assets quickly enough at high enough cost without subsidizing a competitor or startup)

- Industry consolidated enough (or capital costs of the improvement low enough) to finance the upfront cost

I'd guess (no real evidence) it could be because a lot (most?) software runs on timescales where 10% isn't that significant. Also, maybe something to do with Amdahl's law, where speeding up one part by 10% rarely speeds up the whole thing by the same amount?

> Rotor ships take advantage of this same effect by spinning a large vertical cylinder, typically using an electric motor, and using the resulting force for propulsion.

I always thought sails were partially defined by being passive. I wonder why these aren't called "rotor fans" if they're electrically driven?

Is there anywhere it's discussed when rotors are expected to outperform normal fans? They seem to be used only on large ships, but I can't see a first-principles explanation for that.

"Fan" implies the propulsion is in response to air being forced backwards.

These rotors create lift in a forwards direction from the wind blowing across them, a bit like having a fixed wing pointing up.

Regular sails actually work similarly to a wing, in that pressure differentials on either side create a force we call lift on a plane, rather than simply being "pushed from the back" by directly catching the wind. That's why a sailboat can go in almost any direction regardless of which direction the wind is blowing.

Edit: sorry, nevermind, I was confused as to what you were claiming.

Reading the parent carefully, I find nothing that contradicts what you have written in response. Pressure is just force over area.

Thanks, upon re-reading I agree. I misinterpreted the "pushed from the back" statement.

>> A point.

> No. Literally the same point, but in different words and with a feel of authority.

You should consider using words other than "No" if you agree with the point.

I misinterpreted his original point, which I intended to disagree with.

Watching bleeding edge yachts sail is always interesting. Hydrofoils achieve speeds greater than 3x wind speed though their stability doing it is a bit alarming.

https://www.odt.co.nz/sport/yachting/how-fast-can-americas-c...

The imaginary future where huge cargo ships foil under city-sized kites is more impressive than anything I've seen with spaceships.

But you want to make sure you aren't just creating drag you have to fight against. So even with the rotors, the wind direction still matters.

Which is why these things can be stopped and spun the other way.

vortex wings ?

I'm really interested in how dimpling would affect the drag/lift properties of these.

Years ago on /. I saw a post about how wales bumps on the leading edges of their fins/flippers were to increase/modify the eddies around their fins in such a way as to provide them more thrust (or something, it's been years since I read the article) - and I was curious what it would look like to have helicopter blades with leading edge bumps on them similar to wales...

So, I'd like to see what dimples both convex and concave would have on the surfaces if these - like a golf ball.

Also, if you have never done it, take a cylindrical plastic cup and, in a bathtub full of water spin the cup as hard as you can on the surface of the water - like a top - and see how long you can get it to stand up. Kids like this trick.

I always thought it would be interesting to have a barge like flat boat on top of several cylindrical feet like floats, which can spin rapidly along the Z access and use it as thrust.

Mythbusters tested golf ball like dimples on a car, and apparently is help fuel economy.

https://www.autoblog.com/2009/10/22/mythbusters-golf-ball-li...

Yeah, but they are motor driven. So how much of the propulsion comes from the motors, and how much from the wind? Given the relatively small reduction in fuel cost, I'm guessing that most comes from the motors.

The fundamental tech may not be new but the details are, this is lighter and (hopefully) more effective than previous attempts.

> Cool stuff but not exactly new tech

They explain that in the article, and the fact that it newer tech and lighter columns to get a net benefit.

Having grown up in France, I knew about Cousteau's Alcyone (it was a big deal at the time) and had been wondering why it hadn't been used more since then.

Rotor ships predate the turbosail.

Great video explanation: https://youtu.be/XAztqxq2z9k?t=5m50s

First ship was built 1924 so it's almost 100 years old tech by now. Still cool though.

Here's a video demonstrating Flettner Rotos on a boat: https://www.youtube.com/watch?v=__8-QSXgupA

Notably, wind turbine OEM Enercon already used it on one of its transport ships.

https://en.wikipedia.org/wiki/E-Ship_1

Copying the first comment from WSJ 'cause it's interesting:

> These are known as Flettner rotors after the German engineer Anton Flettner who invented them and made the first rotor sailing ship in 1924, with one sailing one across the Atlantic in 1926 - and they are not turbo sails. They have generally been in disuse as it has been deemed that the energy expended in propulsion by Flettner rotors was higher than that for propellers - perhaps it seems with modern materials, wind monitoring and computer assisted controls this has been tilted to the favor of Flettner rotors. Flettner also invented trim tabs which any large power boat operator knows very well.

> An interesting note, Flettner was considered so valuable to the Germans in WW2 that Heinrich Himmler, the head of the Gestapo saw to it that Flettner's Jewish wife was escorted to Sweden for her safety for the duration of the war.

>> An interesting note, Flettner was considered so valuable to the Germans in WW2 that Heinrich Himmler, the head of the Gestapo saw to it that Flettner's Jewish wife was escorted to Sweden for her safety for the duration of the war.

That's nice and all but he still helped the nazis with military research while many of his colleagues fled, Einstein included.

It’s hard to understand, as that’s more or less moving her so he doesn’t kill her.

Great for his fam, bad for the other 8M jews (my grandparents’ families included)

... so Flettner’s a bad guy? (I’ve ancestors who perished there too, you can’t lump everyone, including those involuntarially held, as this situation seems, in the same bag)

Viking Line installed similar 80-foot rotor sail on a LNG powered Cruise Ferry on the route between Helsinki-Stockholm. It reduces power usage roughly 20 percent (900 tonnes CO2 annually). Compared to tankers ferries don't carry significant amount of weight even when they are full. They are basically full of air and 60-100 cars or trucks.

Together with using LNG, periodically cleaning the bottom of the ship, slower speed and connecting to electric grid while in harbor the CO2 emissions are down significantly.

The best way to reduce energy consumption for a ship is to reduce the speed and make thinner ships. This is the new trend in shipbuilding. New cargo ships optimized for slow speed don't have the bulbous bow because it does not increase efficiency in lower speeds.

> Viking Line installed similar 80-foot rotor sail on a LNG powered Cruise Ferry on the route between Helsinki-Stockholm.

Turku - Stockholm, actually.

> The best way to reduce energy consumption for a ship is to reduce the speed and make thinner ships.

Do you mean thinner as in narrower, or thinner materials to save weight? If you mean narrower, I've understood bigger ships tend to have a length/width ratio of about 6:1, as a rule of thumb compromise between seakeeping ability, fuel consumption, cargo space etc. Do you have some more information about design tradeoffs going into such narrower ships?

> New cargo ships optimized for slow speed don't have the bulbous bow because it does not increase efficiency in lower speeds.

Oh, interesting! Any links for further reading on this topic?

Ah yes. you are correct on both counts: Turku and narrower (I had brainfarts).

reading:

https://gcaptain.com/cma-cgms-22000-teu-ships-to-feature-bul...

Just for completeness' sake, the ship is the MS Viking Grace[1]. It's fun seeing the LNG supply vessel AGA Seagas [2] in the early mornings, required since the city of Stockholm did not allow the refueling to happen by tanker truck for safety reasons.

[1] https://en.wikipedia.org/wiki/MS_Viking_Grace [2] http://www.aga.ee/en/products_ren/liquefied_natural_gas/mari...

Another option is skysails (giant kites that drag the ship forward):

https://en.wikipedia.org/wiki/SkySails

Hopefully someday almost all ships have a mix of these things + maybe run on algae-based advanced biofuels or something like that.

Hydrogen fuel cells are looking likely. Solar will probably produce too much electricity for usage during the day, so use that spare energy to split water to create Hydrogen fuel.

I was curious how much sense this actually made so I did the math, sources at the bottom. I suspect my sources aren't perfect, but they're probably close enough to get an idea of things.

Our hypothetical container ship is roughly 400m x 59m, or 23600 m^2, and solar panels generate ~4.5 kWh/m^2 after inefficiencies, giving a total energy generated of 106.2 megawatt hours per day for a ship, if you had a big solar array above all the containers. Assuming an 85% efficient hydrogen fuel cell, that gives you losses both in storing and reclaiming electricity from that storage process. Assuming 1/3 of your energy can be used while generating it and the other 2/3 has to be stored as Hydrogen and then spent to power the energy, losing energy both ways, that leaves you an effective ~81 MWh/day.

Meanwhile the existing engines on that same container ship can currently run at about 90 MW, which means it can output more energy burning bunker fuel in one hour than our solar panels gave us in the entire day.

Container ship size: https://en.wikipedia.org/wiki/Container_ship#Size_categories Energy per day: https://www.quora.com/How-much-solar-energy-is-generated-per... Fuel cell efficiency: https://en.wikipedia.org/wiki/Fuel_cell Container ship energy usage: https://newatlas.com/shipping-pollution/11526/

Clarification: I was talking about using excess electricity from shore based solar units. This would give operators somewhere to dump excess power cheaply (preventing negative electricity rates), all while providing fuel that's easy to store and usable in applications where batteries wouldn't work.

Obviously at this point fuel cells cannot produce the power output that diesel engines can at a given weight. But your power estimates on what a hydrogen fuel cell can do are off by a bit. Some quick searching finds portable 1MW fuel cells, existing 11MW power plants, and a planned 80MW power plant that's being constructed soon in South Korea. Obviously the latter probably weight too much for a ship today, but as the weight comes down that becomes a possibility.

> But your power estimates on what a hydrogen fuel cell can do are off by a bit

My estimate didn't assume the ship left the shore with any hydrogen fuel. I (apparently incorrectly) assumed you meant that the ship would generate its own hydrogen during the day from excess solar while it was in transport.

Ah yes, that wouldn't work at all.

If solar cells got effective enough to generate that much power, you’d probably be better off with solar + battery anyhow.

Isn't hydrogen difficult to store? I've heard that it will leak out of just about everything.

You might be thinking of helium, which becomes a zero viscosity superfluid when cold enough.

Hydrogen can diffuse through certain metals and weaken them [1]. Currently, hydrogen storage is costly and tricky for a number of reasons [2]. It’s also very important to avoid leaks into enclosed areas since it’s extremely flammable.

[1]: https://en.wikipedia.org/wiki/Hydrogen_embrittlement

[2]: https://www.energy.gov/eere/fuelcells/hydrogen-storage-chall...

Oh, didn't know it'd leach into metals, that's interesting.

Edit: I'm wrong, see responses bellow for correction

Original message: I seem to remember (if I'm wrong please correct me) that the Magnus effect works regardless of the direction of the wind, whereas the sky sail needs the wind to be roughly in the same direction of travel.

They could be combined but as far as I understand these spinning columns are more generic

It seems like Magnus sails work best when the wind is coming from the side (port or starboard), since the direction of force is perpendicular to the wind [0]. Doesn't matter which side, since you can just reverse the rotation of the cylinder.

With a headwind or tailwind, tacking could be used but the increased distance traveled may offset the gains from the Magnus sail.

0: https://en.wikipedia.org/wiki/Magnus_effect

You are, unfortunately, incorrect. The Magnus effect doesn't gain you anything other than the helpful drag of a tall cylinder when going in the same direction as the wind. Rotating it only pulls you sideways, which doesn't help.

However, it can pull you forward when the wind is coming from the side. You change the direction of rotation based on which side the wind is coming from.

Without tacking, no (edit: solely) wind power systems will help when going straight upwind.

> You are, unfortunately, incorrect.

No, you are, unfortunately, incorrect.

> Without tacking, no wind power systems will help when going straight upwind.

https://en.wikipedia.org/wiki/Windmill_ship

He was right that "The Magnus effect doesn't gain you anything other than the helpful drag of a tall cylinder when going in the same direction as the wind."

In fact, the Magnus rotors will not provide any usefull thrust is both upwind and downwind scenarios.

https://en.wikipedia.org/wiki/Rotor_ship#/media/File:Points_...

That was not the part of the comment that I referenced.

> In fact, the Magnus rotors will not provide any usefull thrust is both upwind and downwind scenarios.

If the wind is coming from behind won't it simply push the stationary cylinder, adding some thrust?

Rotor ships still need to tack for headwinds, but not to the same degree as conventional sails.

https://en.wikipedia.org/wiki/Tacking_(sailing)

I remember seeing this years ago. Wonder why it hasn't taken off. If their videos are honest in the ease of operation it looks like a great idea.

I've been wondering why shipping companies haven't been doing this for years now. Whenever I brought it up with friends they would say it's probably not worth the effort, but I can't see how it wouldn't be worth it. It's essentially free energy to help move the ship around. Got to say, I feel vindicated by this story.

Inertia is hard to fight. Sometimes all it takes is one player in a market doing it and then everybody else follows/feels they have to also to compete.

That's one reason why Tesla was such a catalyst for the whole industry and EVs. As long as nobody else was really making too much of an effort, everybody could just drag their feet.

Upfront cost of installation, and ongoing maintenance, and the fragility of sails at the time may have prevented them being used before now.

Essentially free energy... except the cost to install, the cost to operate, maintainable and of cause the cost when one of them breaks and causes damage.

For a lot of these “why don’t they just” the answer is simply that they did the math and saw too small an upside for too big a risk.

They are trying this out to see if the overall concept works in practice or if it falls short.

Or they never did the math, assuming it wouldn't work out because of cost to operate, maintain and insure.

I think part of it is needing the technology/implementation piece. Wind power was viable for centuries, but as ships got bigger and bigger, steam/petrol engines became the standard in the shipping industry as traditional sails were no longer viable. Now that we are developing higher efficiency renewable energy technology, we have the opportunity to move full-circle back towards wind power again. However, since these current sails are only supplementing the ship's fuel costs by ~10%, there's still a long ways to go.

> Wind power was viable for centuries, but as ships got bigger and bigger, steam/petrol engines became the standard in the shipping industry as traditional sails were no longer viable.

My understanding is that the main driver in the sail->steam transition was that steam ships were usually faster (and had much less variability in their schedule), and required smaller crews.

The glory of the "last windjammers" was largely enabled by very cheap labor from then-developing countries, allowing them to be competitive on a few select long distance routes.

> It's essentially free energy

The rotors have to be powered. I believe the losses to friction and added mechanical complexity made it unfeasible in the past.

I'd love to see this succeed. The magnus effect is pretty counter-intuitive; it's always nice to see weird physics get used for real.

The interest is rising. Here's the story about Viking Grace, a passenger vessel with the Flettner rotor: https://www.maritime-executive.com/article/viking-line-insta...

Here's a passenger's video about it. It spins quite fast: https://www.youtube.com/watch?v=Ir8YSRhMsXA

Notice the height of the rotors. Cargo ships already have problems clearing bridges in some ports. I imagine that must also be a factor.

I wonder if they could be made to be telescoping or otherwise collapsible.

Magnus Effect.

As sled runners are to wheels, so the wing is to the Magnus effect rotor.

Lift goes up with the square of the radius. Think about that.

I'm in the process of ramping up a toy company that builds and sells kits for Magnus Effect drones.

I plan to just keep making them bigger, first for cargo then for mass transport. It will be necessary to move people efficiently by the million in the decades to come. Already floods and wildfire have begun to increase, soon enough the waters will rise and it will be needful to move our asses.

By using a simple recursive-fractal infrastructure there's pretty much no upper limit. Cf. "Tensarity"[1] and Alexander G. Bell's cellular kites[2]. Also Bucky Fuller's Cloud Nine[3]. Self-powered[4][5].

I imagine huge aerial machines, more like gauzy flying buildings than aircraft, that carry a million or more people at a time. Cities in the sky.

[1] https://en.wikipedia.org/wiki/Tensairity

[2] https://duckduckgo.com/?q=Alexander+G.+Bell%27s+cellular+kit...

[3] https://en.wikipedia.org/wiki/Cloud_Nine_%28tensegrity_spher...

[4] Tethered power generators, "Magenn" company, defunct? https://en.wikipedia.org/wiki/Airborne_wind_turbine

[5] https://en.wikipedia.org/wiki/Vaneless_ion_wind_generator

This should be a big deal for combatting CO2 emissions as well. I believe it was never refuted after it came out a few years ago that ~15 of these ships emit the same CO2 as all cars in the world? https://inews.co.uk/news/long-reads/cargo-container-shipping...

The article says "pollution" not CO2. Given that they burn bunker fuel (very dirty oil left over after things like gasoline are refined away), it's likely the article means particulate or sulfur emissions.

The CO2 emissions are easily estimated and not even close. A container ship can burn 225 tons of bunker fuel per day at normal cruising speed.[1] At a generous 300 days in transit per year (they spend time in port loading / unloading / waiting), that's 67,500 tons of fuel per year. It's a massive number, but a drop in the bucket relative to the 913 million tons of oil consumed by Americans every year, the majority of which is spent on motor vehicle fuels.[2]

Even assigning just 50% of US oil consumption to cars, you're comparing about 450 million tons consumed by American drivers versus about 1 million tons for 15 large cargo ships.

[1] https://transportgeography.org/?page_id=5955 [2] https://www.statista.com/statistics/264825/oil-consumption-i...

https://www.fullwsj.com/articles/maersk-tankers-turns-to-win...

> Fuel makes up approximately 60% of our total cost and this technology has a significant potential to cut fuel consumption by 7% to 10% on the ships that it will be installed."

Jesus, I'm surprised we haven't seen all sorts of crazy ideas coming out of Maersk to reduce this overhead given that it's the bulk of their cost. Wind pillar things seem kinda tame compared to the shit I'd try to pull to save that level of money... Across all vessels no less!!

Wonder why ships aren't trying solar panels and electric motors and auto-pilot... they're out in clear Sun, have a large surface area, and no traffic...

Two problems with boats and solar propulsion: 1) they need 24/7 power. 2) Using a random LG 330 W panel on top of the Edith Maersk, it would take an array 1/3 of a mile by 1/2 of a mile in area to match Edith's 80,000 kW engine power output. Edith is 1/4 mile long and 3/100ths of a mile wide.

Quite a gap, and thats before you start factoring in batteries for the night, structure to support the array, storms...

Though you could power the ship from solar during the night and with diesel generators during the night.

> 2) Using a random LG 330 W panel on top of the Edith Maersk, it would take an array 1/3 of a mile by 1/2 of a mile in area to match Edith's 80,000 kW engine power output. Edith is 1/4 mile long and 3/100ths of a mile wide.

Back of the envelope math says we're short by a factor of ~108. We can get savings in a few places:

(1) We don't have to match the full engine output with solar. Many container ships use super slow shipping at a fraction of the power, [1] says 10% engine load. With batteries you can still increase throughput substantially when needed.

(2) Panels can exceed current ship dimensions, perhaps greatly (tow a long tail of solar panels on floats?). Let's just go for double width and length for now.

(3) Efficiency gains. We're at 20% in back of envelope above but I can get that for my house. Let's say Maersk ponies up for 30% cells.

Still some ground to make up but at least we're in bullshitting distance of claiming it's viable.

[1] http://articles.maritimepropulsion.com/article/Turbocharger-...

> thats before you start factoring in batteries for the night, structure to support the array

Presumably there's some space/weight savings in not having an 80MW engine.

> Panels can exceed current ship dimensions

They really can't, though. Sure, there's plenty of space when the ship is out on the high seas, but any time the ship needs to go into port (kind of the point of a ship) or navigate tight waters such as straits or canals, then the footprint of the panels really has to not exceed the footprint of the ship.

it is not a b/w choice between 100% solar or 100% oil, hybrid solutions could work and address the gaps solar/electric cannot handle,even 10-20% emission savings could mean a lot .

Also it doesn't have to be solar directly, an electric propulsion system which can use hydrogen or high density battery/ storage which plugs into the grid eventually is good enough.

You don't need to drag the cells with the ship, they could be perhaps stationary middle of the ocean and charge the replacement batteries and you could line few such charging stations near the major shipping lines.

You'd need some serious energy storage too. Losing power & steering on the high seas in a storm is bad times.

> Wonder why ships aren't trying solar panels and electric motors and auto-pilot...

https://www.km.kongsberg.com/ks/web/nokbg0240.nsf/AllWeb/4B8...

How would you keep the salt off of them in order to keep them producing optimal power?

There are a few electric ships out there powered by batteries. They have a really short range though and of course a lot smaller than what Maersk needs.

A few examples of electrical ships:

https://phys.org/news/2017-05-norway-self-sailing-electric-c...

https://electrek.co/2017/12/04/all-electric-cargo-ship-batte...

I'm guessing battery cost rather than weight is the main issue here. The Chinese ship is powered by the equivalent of about 24 teslas apparently for a whopping range of 50 miles. Compared to the overal weight of these ships, I could imagine extended range with more batteries would be feasible. I imagine the capital expense is the bottleneck here; not the weight. But it makes a lot of sense for shorter routes.

Having solar and wind to supplement energy might help extend their range by a meaningful percentage but probably not enough to make it worth bothering since you in any case have to recharge frequently; which is probably comparatively cheap (compared to buying fuel)

Wind powered sail drones already exist as well: https://www.saildrone.com/ These are tiny of course but they can be out there for months by themselves. You could imagine a scaled versions of these transporting cargo. With no fuel cost and no staffing cost, you can get economies of scale by simply having more of them rather than bigger ones.

The reason big ships are popular today is that they minimize staff and fuel cost. Big ships require a lot of power but they are overall more cost effective per ton of load than smaller ones. If you take people and fuel cost out of the equation, you can start thinking about different solutions.

This led me to wonder how important height was a restriction on ships. Turns out "air draft" is reported for major ports.

Some interesting findings: The Panama Canal has an air draft of 201 ft imposed by the Bridge of the Americas; the Port of Oakland has an air draft of 220 ft imposed by the Golden Gate Bridge.

Height from waterline does not appear to be typically listed for ships, but I would guess that most cargo vessels do not have 100 ft of clearance to spare. I think this means these sails would only be fitted to vessels which generally don't care about height restrictions (e.g. ships larger than Panamax) or ships running predictable routes.

https://en.wikipedia.org/wiki/Air_draft

I believe the unloaded freeboard of a typical containership is 80-100' The bridge (navigation deck) is higher, but the "sails" would be mounted from the deck, so I expect most ships would be OK.

Right, but container ships are stacked with containers higher than the top deck. So maybe this only makes sense for tankers and bulk carriers, or any large cargo vessel that is not a container ship.

Calling these sails is a stretch, and IMHO just an attempt to market them as more "green" than they really are.

They may as well be propellers. It's great to improve the fuel efficiency of these vessels, but the word sail evokes a mental image profitably inconsistent with reality.

What these ships are mostly surrounded by are waterfields that go as far as you can see. Can they come up with some sort of rolled flexible solar panels that once ship goes into full sail they release their “solar tail” behind that floats on the water surface and captures sun and turns it into electricity for ships’ engines?

I mean 300 meters square of solar panel should be sufficient to push the ship at its nominal speed. For free!

I think the issue would be salt water. Salt water destroys everything, I can’t imagine that a PV array floating in water would have a good life expectancy.

On the plus side, if the insulation fails you could turn container ships into accidental fishing boats.

> Salt water destroys everything

This is the statement I hear relating to all kinds of ocean-based renewable energy ideas. Sources are never provided.

The problem must have to do with economic viability and the replacement/maintenance costs exceeding savings.

Could you supply sources to elaborate on where the break even point of solar tail (or any two other ocean renewable energy) systems would be as relates to costs and benefits?

Edit: I don't really want to argue whether or not steel rusts in saltwater. My argument was that the break-even point of a "solar tail" is dismissed out of hand without sources because of land-based technologies being considered as the only ones.

> Sources are never provided.

We also do not need to provide sources for statements such as 'water is wet'.

Anything on a boat, or even shoreside near to the ocean is subject to corrosion and corrosion protection is a serious maintenance issue. I've lived 2 km from the sea and even there the nails would rust right out of the building due to the salt that the wind would carry in.

Yes, salt water is corrosive. And yet, there are metal ships with viable lifetimes. This sub-thread is a bit less helpful than I am asking for.

Edit: Come on. It's not impossible to engineer for ocean use.

Wave power generation: https://www.bbc.co.uk/news/uk-scotland-scotland-business-250...

Longer term: https://en.wikipedia.org/wiki/Submarine_power_cable

Salt water is so corrosive that there is a whole branch of materials science dedicated to coatings and all kinds of other anti-corrosion measures such as galvanic protection using sacrificial material. The evidence is overwhelmingly on the side of statements such as 'simple systems that work well on the shore need extensive rework for ocean deployment assuming they can work at all'.

Even a simple scratch is enough to lay all your carefully produced work to waste.

Agreed that the environment is vastly different than on land, that a scratch through a coating is akin to no coating at all, that anti-corrosion measures are a constant vigil in oceans.

But I asked for sources treating the proposal in the original comment, and got told that "water is wet".

It’s obviously not impossible, it’s just expensive, which is a problem in the given context.

How big is the check and why? That's what's so hard to get an answer for when people are determined already to not to try. I mean, I guess I have Google and a long-weekend. I was hoping for someone to drop an URL that can explain this and provide key terms.

Throw out a speculative idea, get a speculative answer.

Dunno why you’re expecting me to go all civil engineer on you, nor do I understand why you’re acting like I’m the barrier to the idea being tried.

Go do the math yourself, it’s your idea.

It wasn't my idea. My idea was that it shouldn't be dismissed for the reason you presented without a citation.

What can be asserted without evidence can also be dismissed without evidence.

As there's a well known consensus that some factor (e.g. saltwater caused maintenance issues in this particular case) tends to be a game-breaker, then it's perfectly reasonable to dismiss 'without a citation' ideas that encounter this factor if the idea has no mention/citation of how they're going to fix, avoid or tolerate this.

If there's a plausible-seeming way that the idea can work despite the obstacle, then by all means we can discuss if that way will be sufficient or not; but if the idea simply ignores major problems, then there's nothing to discuss.

Point taken regarding your first line, though that sword would cut both ways I think. See https://news.ycombinator.com/reply?id=17886400 regarding the second and third.

There’s a reason why pictures of “beautiful” beach front houses are usually from a long distance away: they are usually in pretty rough shape.

My request was not intended to be asking for sources about corrosion, but for sources as to why corrosion should be the limiting factor. I would edit it to lead with the question it asks in the third line, if it weren't now too late.

Here's a source for you that mentions that even some typical formulations of stainless steel are susceptible to corrosion in saltwater:

https://www.clintonaluminum.com/304-stainless-steel-in-seawa...

White bread is bad in saltwater too, that doesn't mean there aren't better materials for the application.

https://www.quora.com/Does-aluminium-react-with-salt-water

https://en.wikipedia.org/wiki/Organic_solar_cell

Salt water destroys everything so don't build boats guys

That's the point of the source you requested and I provided: there are some formulations of stainless steel that are actually kind of ok in salt water despite most being poor.

No one is arguing that it's impossible to build a bear with solar panels. The point is that you can't slap a cheap panel from Alibaba on a float and have any assurance that it will work reliably. Thus costs go up and the whole idea may become infeasible.

I don't have a source, but as an engineer working for the US Navy, we are frequently told that the Navy spends an enormous amount of money on corrosion control. Like, in the billions to tens of billions of dollars per year. As a consequence, corrosion control is a significant fraction of the Navy's R&D budget.

https://www.gao.gov/assets/650/647926.txt

https://www.onr.navy.mil/en/Science-Technology/Departments/C...

Thank you.

How would you keep them clean enough to produce optimal output? Every drop of salt water would quickly dry and leave a salty residue. How do you clean that while at sea?

I am not the author of the original comment, but I really like the concept. From what I understood this would be floating at surface level and would be continuously washed over by surface water.

There are many good objections. It may be that the original comment does not illustrate the promise of this energy platform very thoroughly.

For free, when there are no waves, when the sun is shining, when there is no other vessel that crashes in to them and when you convince someone to make it all and then gift it to you.

300m^2 only gets you a couple hundred kW on the brightest days at peak efficiency. These ships require powerplants providing on the order of 50,000 kW.

A 40-acre floating solar farm would add a LOT of drag. Better to make the solar farm stationary, use it to synthesize fuel, and run the ship with an internal combustion engine for power density. Maybe someday batteries could be used.

I believe you. The difference between required and available power is large.

Can you provide sources that derive/explain/summarize the figures you present so that others may better understand the reasoning?

Sure, sorry.

The rule-of-thumb max for solar irradiance is 1 kW/m^2 (noon, clear day, low latitude, etc):

https://en.wikipedia.org/wiki/Solar_irradiance#Irradiance_on...

The rule-of-thumb for the electric power output of a solar cell is about 20% of the irradiance.

https://en.wikipedia.org/wiki/Solar_cell_efficiency

And because this drops in the morning and evening and falls to zero at night, you realistically only get a bit more than 1kWh/day with a 1 m^2 solar cell.

And these ships require huge powerplants. Maersk's biggest ships use this engine:

https://en.wikipedia.org/wiki/W%C3%A4rtsil%C3%A4-Sulzer_RTA9...

which outputs over 80 MW.

No citation for the drag caused by a floating mat of solar cells. The fact that these enormous ships burn this much fuel should be evidence that dragging a much more enormous mat should show that dragging an even more enormous and more draggy mat would be a non-starter.

Thanks!

My acceptance of the idea that drag might be manageable has to do with volume displacement and not surface area.

A long shallow "tail" could exert orders of magnitude less drag (vis a vis surface area) than a deep heavy hull pushing up a big wake. (Related to why boats are long and narrow...)

https://en.wikipedia.org/wiki/Wave-making_resistance

Edit: The fact that you see that as a clear non-starter has me wading into Google results for hydrodynamics. It is definitely over my head, but I am curious. Is there a rule of thumb for drag in water that I'm not finding?

https://www.boatdesign.net/threads/wetted-surface-area-appro...

http://www.engr.mun.ca/~bveitch/courses/r-p/Assignments/ITTC...

http://www.fade.up.pt/cifi2d/files/effect-of-wetted-surface-...

My assertion that it's a non-starter is based on the area of an 80 MW solar farm, not hydrodynamics. 80,000 kW x 24 hours / 1 kWh/m^2 = 2,000,000 square meters of solar cell area.

That's a lot. In contrast, the ship has an area of 24,000 m^2. A light-weight solar system might weigh 10 kg/m^2, so the whole thing weighs 20,000 tons. The ship has a staggering capacity of 200,000 tons.

So yes, it can carry it, but the 'long shallow tail' is really long - literally 20 miles, if it's the same 60m width as the ship - and really shallow. Maybe that's low drag, but if so, why wouldn't they build ships like that?

That is an interesting result. A 20 mi long piece of electronics floating in the open ocean would have [:deadpan:] more prohibitory issues than drag. Even if it were more optimistically estimated, this has obvious maneuverability (not to mention production) problems. They build ships the way they do for smart reasons, but I do like to explore the possibility space.

The application that no one will ever pay for might be a permanent, autonomous, very large, plastic garbage consuming vessel in the Pacific Gyre.

The form factor is less a limitation (in theory) than the will to allocate resources in such a way.

Somebody made a way to start cleaning this up, and a proposal to pay to do it (front page 3 days later):

https://news.ycombinator.com/item?id=17899395

I'm guessing that you're underestimating the cost of drag ... tailing a 300 sq meter "boat" would probably require more energy than it could produce. I have no data, and haven't done any back of the napkin calculations to back up my stance ... but just look at the speed difference between a monohull vs a catamaran vs a foil sailboat. Reducing the contact area with the water (and thus reducing drag) is _everything_.

Drag increases with the square of velocity [1]. Some of the ships might be able to travel much slower? I keep asking for sources because dismissals out of appeal to obviousness are so ubiquitous.

[1] https://www.lmnoeng.com/Force/DragForce.php

Edit: Admittedly, you may be right, but without even back-of-the-envelope calculations, and with the assumption that these boats must go as fast as possible, I don't know why.

I too freely admit that you might be right as well (if the assumption of speed can be dismissed) ... lol, this feels like it would be perfect fodder for one of those physics youtube channels that answers channels, or perhaps XKCD's https://what-if.xkcd.com/

I think you're vastly overestimating the power output of solar cells.

Using 20% efficiency panels gives us 0.2KW/m^2/hr.

According to this Quora answer [1] a small container ship uses 15,000kW: for one 24 hour day that means it needs 360,000KWH in energy.

If we assume 10 hours a day of full sunlight then we need 180,000m^2 (equivalent to 18 hectares or 44.48 acres or 33.7 football fields) of solar panels.

This of course overly optimistic as it assumes no drag nor increase in power needed to haul these solar panels (and batteries for use overnight, etc.).

[1] https://www.quora.com/How-much-does-it-cost-to-fuel-a-cargo-...

Nitpick, but 0.2KW/m^2/hr would be an acceleration, not a constant rate. You mean 0.2KW/m^2 - this is constant power output. W already includes a per-unit-time component. I'm nitpicky on this topic because of how many professionally-written articles I've seen make similar mistakes.

I think you're under-estimating the power of the square. 180,000m^2 is 2 x 300m x 300m.

To entertain the strongest interpretation of the idea, for purposes of understanding the reasoning: consider a very large, very slow ship trailing a towed PV array not made of steel [1], additionally harnessing sea-surface energy, and the extension/retraction of the tow cable [2, 2.5], made from non-corrosive plastic or plastic-coated materials, that costs hypothetically nothing to maintain, but must be completely replaced every 10 years.

What are the specifications of such a system that it would generate sufficient power to cost-effectively augment or replace internal combustion, and what would the viable price-point for installation be considering costs of bunker fuel? Other comments [3, 4, 5] added the kind of information that might help to answer that. I am interested in sources, and discussion which isn't immediately dismissive of something unproven.

Put another way, how much would low-grade petro-fuels have to cost before this became a viable alternative, and what sources support your conclusions?

[1] https://en.wikipedia.org/wiki/Organic_solar_cell

[2] https://en.wikipedia.org/wiki/Wave_power

[2.5] https://www.tugtechnologyandbusiness.com/news/view,hybrid-pr...

[3] https://news.ycombinator.com/reply?id=17886124

[4] https://news.ycombinator.com/reply?id=17886177

[5] https://news.ycombinator.com/reply?id=17886190

Edit: spelling

Edit 2: added a reference

A typical 250W PV panel is 1.6m^2. 300m2 of these will give a peak power of about 47kW which is about 63hp.

for comparison a Wärtsilä RTA96C is rated for over 80MW which means you'd need over 0.5million m^2 of PV panels to match this. (about 85 football pitches).

Feasible but expensive

The idea that it would need to be 1000X bigger is helpful. The original poster's figure of 300m^2 does not make much sense.

Rereading with the principle of charity in mind, I think the original poster meant (300m)^2, though it was not clearly so.

My small 12 meter long boat has a sail area of 900sqft. When sailing perpendicular to the wind it captures pretty much all of that.

The sail on that ship is 100' high, and looking at the aspect is around 15' wide, or 1500sqft. That type of sail I think only harneses half of that area, so half of 1500' or 750' best case.

I can say with complete confidence that if all the energy from two of my boats were towing one of those ships, even in a hurricane, it's going to increase fuel efficiency by approximately 0.0%

EDIT: I just did a random sample of wind speed [1] of points on the globe on international shipping routes [2] and it looks like they are generally around 10-15km/h. Thats barely enough to get my boat up to speed. There is a reason sailboats take very particular routes and don't just go from point A to B

[1] https://earthjustice.org/sites/default/files/world-cargo-shi...

[2] https://earth.nullschool.net/#current/wind/surface/level/ort...

These use rotor sails, which are different than what you have on your boat. Unless of course you also have rotor sails?

Noting the use of the plural, How many are installed on the ship? We see two(?) in the photo? What’s the practical limit?

> has installed 100-foot-tall rotating cylinders on one of its product tankers

found this video explaining it https://www.youtube.com/watch?v=2OSrvzNW9FE

https://en.wikipedia.org/wiki/Magnus_effect

I hear this is what Nautilus Labs is trying to solve https://nautiluslabs.co

In a different related article I learned that Ro-Ro vessels are Roll-on Roll-off cargo vs Lo-Lo vessels which are Lift on - Lift off.

And I thought IT loved acronyms.

Amazing, new, disruptive technology for shipping...

Now who has the patent on SAILS!

This kind of reminds me of constant remakes of Spiderman ;0)

Was hoping to see more than 10% reduction. Seems fuel prices could easily absorb that quickly.

A little embarrassed to ask but why would normal sails not work?

I don't know, but this looks very space saving and have much less moving parts.

maintenance. the materials used for actual sails stretches eventually and is less effective. presumably these towers have very little to replace.

They have a very expensive, hard to replace, and high maintenance bearing at the base of the tower that carries the full force of the sail leveraged by a long moment arm. This bearing (along with lack of height = low wind) has been the reason that Flettner sails and wind turbines haven't been economical in the past.

I guess too labor intensive, and probably problems scaling up to the size of current ships. Consider the last generation of sailing cargo ships before steam took over (https://en.wikipedia.org/wiki/Windjammer ), those were around 2000-5000 GRT, compared to a big container ship today at something like 170000 GRT. The tonnage difference is rather massive.

Also, if you look at pictures of windjammers, masts, rigging etc., would get in the way of cargo handling. Less so on a tanker compared to, say, a container ship, of course.

How loud are these when they are rotating?

Think of the PR we could harness with this alternative energy source!!!

wouldn't it help to add little shovels for friction?

SAILING FOR THE WIN

Would be excited to see this technology combined with the "underbelly bubbles" technology that I heard about a few years ago where they reduce drag by releasing air bubbles under the hull. Yeah it takes energy to do it but the decreased resistance is supposedly a net gain. Two 10% gains would be awesome.

Some fleets have implemented special bottom paint to reduce drag by reducing algae growth.

I wonder how long a magnetic cleaning robot could survive on the hull of such a ship.

After manned narco subs and towed sub capsules were mitigated by new police efforts drug traffickers experimented with magnetically attached parasite containers on the side of large shipping boats. But they didn't have to move.

How do they mitigate narco subs? Sonar patrols I presume?

From TFA...

> Maersk Line spent around $3.4 billion on fuel last year for its fleet of around 800 vessels.

Wouldn't savings from wind power be bad for the petroleum industry? And therefore by lobbyist extension bad for everyone?

That's Maersk Line, which is the container shipping division of Maersk. The rotor sails are being installed on a tanker vessel from Maersk Tankers. Deck space is a valuable commodity on a container vessel, so not as obvious where to place the rotors.

I quoted that line exactly from TFA. (the friendly article)

I am sure you did. That doesn't make it any less misleading.

Reducing operating costs often leads to higher overall demand.

Not at all, energy used transporting energy is wasted and works to reduce EROEI.

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