Wind-powered ships are making a comeback | Hacker News Reader

Wind-powered ships are making a comeback

amp.economist.com

92 pointsOsiris3064 comments

This idea was already broached at HN in

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

https://news.ycombinator.com/item?id=17885284

But a question arises as to practicality of this configuration in extreme weather at sea. That's a lot of wind swept area aloft abovedeck. In extreme weather conditions with rolling seas, an elongated cargo vessel such as a tanker will be subject to sagging (central portion suspended in space between two wave crests). Given strong head or tail wind force imposed on tall rotor shafts it would seem that extra torque would be imparted on the central section increasing the liklihood of hull failure under full cargo load.

I would guess that the bending and twisting pressures of swelling and crashing water, rather dwarfs the potential forces the cylinders can drag through air in a storm, especially while they are not spinning. And I'd guess they would be engineered to break off, before harming the hull if that could be a threat.

Fairly sure this is an naval architecture problem a company of Maersk scale would be able to solve. There may be additional strengthening installed whilst the sails are installed. Seems like a ‘use more steel’ type problem.

Yeah, presumably so. But most articles of this sort tend to be more like one-sided sales pitches. Personally, I'd fall over if I saw an article which adopted a Kantian 'thesis' 'antithesis' ergo suggested 'synthesis' approach.

Hegelian, you mean. Kantian argument would be pretty boring, as it's typically exhaustive.

Exhaustive to the extent practical would be nice :)

Is that smart way of saying present both sides of the argument? I tend to work in 'more steel' type problems ;)

You quit spinning the rotors and they stop acting like a sail.

I wonder if they have enough rotational inertia to cause gyroscopic effects while they're spinning. I wonder if it could be used to stabilize the ship. Or it causes more issues than it solves you can just stop spinning it, just like you can stop it to stop it acting like a sail.

Without running the numbers, just looking at the mass of the sail vs. the mass of the ship, is say the effect is neglible.

I know of a company that makes these as retractable spinning cylinders

The PDF that @danielvf posted mentions gyroscopic benefits on page 20.

In heavy enough weather it's possible to drop sail entirely and still make way on a bare mast, so nah, they might act less like a sail, but they don't stop entirely.

In heavy weather a sailboat sails under bare poles. However, it might actually be a stabiling force in rough seas. My sailboat is far more stable with the sails up. Side to side rolling is eliminated.

Some more info on the actual tech: https://www.norsepower.com/technology and https://www.norsepower.com/rotor-sail-solution

Obligatory wikipedia entry: https://en.wikipedia.org/wiki/Rotor_ship

A different but interesting concept: https://www.skysails.info/skysails-marine/skysails-antrieb-f...

Good demonstration of the Magnus effect: https://www.youtube.com/watch?v=QtP_bh2lMXc

This is the video they reference at the end that elaborates and shows off the use in ships, as well as some planes that have spinning cylinders instead of wings: https://www.youtube.com/watch?v=2OSrvzNW9FE

If petrol for ships was taxed like petrol for cars, this would have already been common place.

Hell if petrol for planes was taxed like car-petrol they bring back zeppelins!

oh the humanity

For some actual numbers from a real freighter with four Magnus effect columns on it, check out this pdf https://www.ship-efficiency.org/onTEAM/pdf/06-STG_Ship_Effic...

This article is a bit lacking in the visual imagery department (that picture in the article is super old) - here's a youtube link from Norsepower (the article says they're the manufacturer):

https://www.youtube.com/watch?v=FUCShEXkpL8

Current location and some before and after pictures - https://www.marinetraffic.com/en/ais/details/ships/shipid:73...

I recall back in the 80's someone made a freighter with a computer controlled sail on it. It was written up in Popular Science (?) as the future of freighters and tankers. Never heard about it again.

IIRC it turned out to be impractical and was shelved after the test runs.

I question whether the cost of doing this in new novel naval architecture isn't excessive. You can have a green ship without installing Magnus effect rotor sails:

A) install a massive ground mount photovoltaic system

Or massive wind farm on land.

B) use the kWh from it to crack water into pressurized tanks of hydrogen

C) transport the hydrogen to the ship, store it onboard, and run it through fuel cells to drive electric azipods.

This require the engineering resources for on board hydrogen tank system, fueling system and fuel cells. Less mechanically complex than massive rotor sails, and something that all of the subcomponents exist for "off the shelf".

This lets you use otherwise useless, non arable land for the energy generation. Even if the electricity to hydrogen process is extremely inefficient. At a certain point if you plot the ongoing price drops for massive grid scale PV, when PV panels hit $0.20/watt, it will be economical.

Hydrogen plumbing is not really a solved problem so I challenge the "less mechanically complex". Those hydrogen atoms are really small!

The margin on shipping is low enough that I suspect they looked at everything they could get off the shelf before settling on this one, which I agree is complex. It will be interesting to see the long time life of these sails.

> I question whether the cost of doing this in new novel naval architecture isn't excessive. You can have a green ship without installing Magnus effect rotor sails:

> A) install a massive ground mount photovoltaic system

> Or massive wind farm on land.

> B) use the kWh from it to crack water into pressurized tanks of hydrogen

Or, though it's in a different sense of "green ship": provide the power generated by the solar array / wind farm very cheaply or at-cost to offset the emissions generated by the ship. It doesn't make the ship emissions go away, but it could make something that's grid-connected become carbon neutral.

The Magnus effect is pretty cool. I firs came across it when watching this video which shows how effective it is by dropping a ball from a height while spinning it. https://youtu.be/QtP_bh2lMXc

Would wind turbines make more sense? It seems like they’d be catching a larger cross section of wind.

I believe its possible, with stability being the big problem. Self stabilized, floating, tethered and large scale wind turbines are already being built[1] - so its something to look out for in the future.

[1]https://www.equinor.com/en/news/hywindscotland.html

On the flip side could these replace conventional wind turbines to generate electricity?

Hard to imagine how. They use wind to generate a linear force. We like to have rotational forces to feed generators.

We have lots of ways to turn linear force into rotational. My car engine would like to have a word with you.

Off the top of my head. Hook it up to a crankshaft. On the push stroke turn the motor on and capture the wind. On the pull stroke turn off the spinning and let it return to vertical.

Magenn Power, Inc. (now defunct maybe?) was building tethered aerial generators.

Just search for "Magenn" with two 'n's.

Interestingly the problem tends to be economical rather than technological. A 5 years ROI would normally be sufficient to get traction. Apparently the current system of charterers is holding it back.

What about populating building tops with these ?

Are your buildings moving around and eating each other like that recent dystopian SF work, a la Mortal Engines?

It would require quite long devices to move.

It seems prudent to invest in some low-tech solutions, just in case resource-intensive high-tech solutions fail us in the long run.

Rotor sails aren't really low-tech though, the original pre-WWII attempts failed because the sails were too heavy and the engines (to rotate the "sails") not efficient enough, so the rotor sails were a net energy loss (aka using the engines to power regular screws was more efficient even in best-case scenarios).

The new attempts (since the mid-augths) use advanced modern material science to build the sails, no way you can replicate that in a low-tech non-industrial context. It's way more complex than an ICE (and in fact requires one to power the rotors themselves).

why use the amp link? Firefox on Android won't open

And again, they try to be cheaper by manufacturing in China. When do we realize that this is a trap we created for ourselves...?

Why wouldnt we want to manufacture everything for less?

Supply-chain control. Technical knowledge. Innovation capacity.

I really want this to be a thing, but my rough calculations given the total cross section area of the sail and the average wind conditions on shipping routes come out to as close to nil as makes any difference for ships these size.

I posted a very rough calculation on the last HN post about this and got downvoted for some reason. I guess everyone else wants this to be a thing so much they are happy to set aside physics through sheer force of will. HN people and the investors / instigators of this project.

This is one time I'm desperately wanting to find out I'm completely wrong.

My last post in a nutshell - these things are order of magnitude the same size as the sail on my own sail boat. Forget about the type of sail. Even if 100% of that wind energy was converted to forward motion it's going to do essentially nothing in the context of a big ship.

Do you have numbers to share? Link to your previous post?

It looks like it's being installed on the Maersk Pelican - a "small" tanker. https://www.marinetraffic.com/en/ais/details/ships/shipid:73...

I think I've heard that in, general, wind gets quite stronger the higher the sail is. Is this in your calculations?

No I don't, my calculations at this stage are as follows:

Sail area - same as my 10 ton boat. Gets me to 7kts in a good strong wind.

Boat they intend to install it on: 110000 tons!

My point is that for this to have any impact at all, a massive amount of energy has to be extracted from the wind. An amount of energy that just doesn't exist in the volume of moving air they are talking about.

I'm still baffled by this.

This is more complicated - you ignore hull speed for one. Amount of force needed to move ship through waves is non linear: https://en.wikipedia.org/wiki/Hull_speed

These things are not vaporware [1], and the claim (by experienced operators) is a fairly conservative 7-10% fuel savings.

[1] https://en.wikipedia.org/wiki/Rotor_ship#/media/File:Uni-Kat...

I understand that, in fact probably uniquely to people on this thread I've been on a rotor sail boat (not sailing though, in dock).

They do work when the ratio of the sail area to the boat is appropriate. In the case of the one I went on it was a very efficient hull too - very light weight catamaran.

The ships in the article you link have huge sails on reasonably small ships. The ones suggested by Norsepower are absolutely tiny compared to the ship. They are, like i've said, about the same cross sectional area of a small pleasure sailing yacht on huge container ships.

You were downvoted because your calculations were for regular sails, and sailboats, instead of for Magnus effect.

Wikipedia says:

    F = L*rho*v*2*pi*r^2*omega

where L is the length of the cylinder, rho is the fluid density, v is the fluid velocity, r is the cylinder radius, and omega is the cylinder angular velocity.

What angular velocity are you assuming in your calculations?

My back of the napkin assumed all energy from the wind over the entire cross sectional area.

Magnus effect or not, i'm just dealing in orders of magnitude and for the average wind speeds on shipping routes, I just don't understand how this works even if 100% of the wind energy is extracted from the cross sectional area of the sail.

[Snipped after looking at how it works again]

No, I don’t think that’s what it’s doing. It’s actually powered - using electricity to make it spin. As a result of the spin, it creates vortexes that push 90 degrees to the wind.

Yeah I think I was still confused about how it works, but I've just decided to snip out my comment instead.

After looking at the math a bit (including the one helpfully provided above), I think you're missing alot by ignoring the effect of the rotational velocity when thinking about this effect. The spinning rotation has a multiplier effect on the air movement similar to a how a much larger/fuller sail could redirect the air flow to produce more forward motion in a traditional sail.

[Edited] The effect is similar to how a rotational wing aircraft also produces lift that is not strictly proportional to the area of the wing (although for different reasons).

Without seeing your back-of-napkin numbers it’s hard to know where you might be going with this, but the idea that sail efficiency has something to do with the amount of energy in the wind in a particular cross section seems in need of justification. You’re probably better off considering air/sail interactions as a momentum transfer - the goal of the sail is not to extract all of the energy from a packet of air (presumably leaving blocks of frozen nitrogen in the sail’s wake), but rather to extract as much forward momentum as possible out of the interaction, leaving the air with more rearward momentum than it started with.

These green-washed headlines are getting absurd.

Wind-powered suggests there's no fossil fuel based propulsion, when these rotors are driven by the same propulsion system as the ship's propellors: diesel.

Wind-powered suggests that motile power is provided by the wind, which is the case here.

Surely a sailboat with electrically controlled surfaces is still wind-powered?

There is still a diesel engine in the loop, which if turned off makes the ship not move.

These are like electric hybrid cars which are sometimes thought* of more valuable than increased efficiency of burning gas (which is all they boil down to)

*at least I used to think that. Maybe I'm the only one.

> There is still a diesel engine in the loop, which if turned off makes the ship not move.

So it is with my sailboat example?

> These are like electric hybrid cars which are sometimes thought* of more valuable than increased efficiency of burning gas (which is all they boil down to)

Most hybrid cars are plug-in, you can charge the battery directly and use mixed-electric mode or even exclusively electric mode for short distances.

Most sailboats operate fine if the engine is off.

It may be that plugin hybrids are more numerous now, but for a very long time most hybrids did not have the plug in option.

They're just slightly improving the efficiency of a grossly inefficient system.

When wind becomes the dominant propulsion force, then it becomes appropriate to start using terms like "wind-powered".

As-is, this is just PR.

These vessels burn copious amounts of awfully dirty bunker fuel with basically zero emissions control systems. If you've spent any time downwind of such ships, you would better appreciate how offensive the green-washing of this relatively minor improvement really is.

Just sailing downwind of a cruise ship idling at port is noxious enough to make one nauseous, and it isn't even under load.

The whole industry needs a hard reset in the emissions department.

Basically any commercial transportation venture traversing international air/seas operates in a regulatory void and takes advantage of it wherever possible, at the expense of the planet.

Reply on news.ycombinator.com