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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

#51

Post by kenneth »

kitd wrote: post #14
jessriedel wrote: post #10

Earlier quoted context omitted.

> 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 onl…

"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.

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

#52

Post by danaos »

jacquesm wrote: post #35
LeifCarrotson wrote: post #32

Earlier quoted context omitted.

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) wi…

> 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_...

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

#53

Post by jtuente »

alex_duf wrote: post #24
IB885588 wrote: post #8

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.

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

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

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

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

#54

Post by gardaani »

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.

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

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

#55

Post by telchar »

a_c_s wrote: post #45
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 cou…

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.

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

#56

Post by jacquesm »

cwmoore wrote: post #49
jacquesm wrote: post #39

Earlier quoted context omitted.

> 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.

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

#57

Post by jacquesm »

danaos wrote: post #52
jacquesm wrote: post #35

Earlier quoted context omitted.

> 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.

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

#58

Post by telchar »

cwmoore wrote: post #30
village-idiot wrote: post #21

Earlier quoted context omitted.

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…

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...

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

#59

Post by dmoy »

heywire wrote: post #50
jherdman wrote: post #33

Earlier quoted context omitted.

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...

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

#60

Post by cwmoore »

telchar wrote: post #58
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…

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

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