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

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

#41

Post by siruncledrew »

ValleyOfTheMtns wrote: post #23

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.

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.

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

#42

Post by bovine3dom »

ValleyOfTheMtns wrote: post #23

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.

> 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.

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

#43

Post by CodeCube »

joering2 wrote: post #19

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…

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_.

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

#44

Post by cwmoore »

LeifCarrotson wrote: post #37
joering2 wrote: post #19

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…

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?

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

#45

Post by a_c_s »

joering2 wrote: post #19

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…

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-...

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

#46

Post by curiousDog »

spydum wrote: post #11
curiousDog wrote: post #7

Earlier quoted context omitted.

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.

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

#47

Post by cwmoore »

CodeCube wrote: post #43
joering2 wrote: post #19

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…

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.

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

#48

Post by taneq »

robfitz wrote: post #9
fmsf wrote: post #2

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.

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 "avera…

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.

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

#49

Post by cwmoore »

jacquesm wrote: post #39
cwmoore wrote: post #30

Earlier quoted context omitted.

> 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…

> 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

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

#50

Post by heywire »

jherdman wrote: post #33
abtinf wrote: post #18

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 mainte…

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!
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