A cargo ship's 'WindWing' sails saved it up to 12 tons of fuel per day | Hacker News Reader

A cargo ship's 'WindWing' sails saved it up to 12 tons of fuel per day

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83 pointshotdailys69 comments

So, they are saving 14% and expect to multiply that by 1.5 by having an additional wing. Is there any prospect of getting near 100%? Naively 15 wings would get there. From the image maybe 7 would fit on this ship without a redesign. Once it's proven, will it gradually evolve to taking more and more of the energy requirements?

Obviously I realize there has to be some fuel in case the vessel would be becalmed, but apart from that, what are the limits?

You can fit that many, maybe, but most of them won’t be able to effectively harness the wind as the other sails will interfere.

Yeah, was wondering about that. Once you have to start extending the deck or mounting them on tugs the trade doesn't seem likely to be favourable.

Why stop there? Add more than 15 sails and you could be generating fuel!

> Why stop there? Add more than 15 sails and you could be generating fuel!

AFAIK there are a few companies that have been adding electric drive systems to sailboats that actually do work this way, not only can it be used to maneuver around when the wind is uncooperative but it can generate power when the wind is good, basically acting as a "hybrid" of sorts where hypothetically given enough battery storage and maybe some solar it could be possible to never have to plug in or run a combustion generator.

Why not put a windmill on the ship and generate electricity, turn the screw, and drive the ship? Not as efficient?

If it works what prevented ancient people from building windmill ships?

likely lots of moving parts with a less-than-ideal place to be conducting regular repairs

My guess is it's a "equal and opposite reaction" sort of thing.

They're saving 12%, on the best days. The average is 3.8%.

What's not covered in the article is the weight of the devices and the amount of cargo that must be removed from the load to support them. Without that you can't project forward at all.

And even so, you're never going to get to 100%. Cargo ships need electricity to keep cargo refrigerated. They need to be anchored for long periods of time. They need to navigate harbors and other channels.

> They're saving 12%, on the best days. The average is 3.8%.

According to the article it is 12 tons/day on the best days and 3.3 ton/day average. 14% average with 37% max for reduction of greenhouse gases emissions.

Where are you getting these figures? They aren't the same as the ones in the article.

100% of what? In principle with favorable winds a large merchant ship could cross an entire ocean using sail power, but it would be very slow. Due to capital expenses, crew wages, and customer demands that wouldn't be economically viable. Even with "slow steaming" to save on fuel, merchant ships on long crossings are generally cruising at least 13 knots. There's no way to consistently hit such a high speed on a large vessel with any practical sail rig.

> Is there any prospect of getting near 100%?

A sailboat. The word you are looking for is a sailboat.

Sailing cargo vessels have a number of issues with economics, which is why we stopped using them 75 years ago. There are some people using them in limited capacities, but for the most part we can't replace our global shipping with them.

Speed is one. Even the fastest sailing cargo ships, which carried very limited cargo averaged 15ish knots on favourable routes. Modern motor cargo can travel at 20+ knots on almost any route.

Even the largest metal hulled sailing ships that lasted until the 1950s carried an order of magnitude less cargo than a small container ship today. And take more crew to handle.

The other issue is that sailing to windward is still not solved by this, and just from looking at the design, I would guess that it actually decreases fuel efficiency on any route that requires you to go into wind.

The other problem with stacking more of these onto a ship is that you have to counterbalance both the weight and the lateral forces. Sailboats do this with a keel. Adding a keel to a large bulker like these is expensive, and will limit the ports you can visit due to draught, which will already be limited by the enormous sail keeping you from transiting under bridges.

Cargoships would gladly go slower if they burn less oil. In fact they generally opertate nowhere near their top speed for this very reason.

Yes, but slow-steaming for efficiency on a cargo ship is ~18 knots, which is still above the upper speed of the fastest sustained speed of sail cargo vessels. You can slow further for efficiency, but you hit a tipping point pretty soon where you end up costing yourself more in time than you save in fuel.

Realistically, a sail cargo ship is going to move along at a rate less than 10 knots.

And of course this is all on a route with favorable winds. If the winds are against you, all bets are off.

The same is true of these wingsails, there are limited routes where they will be efficient. Anything going up-wind is actually going to be a loss.

Drag when sailing into the wind and going under bridges, as well as not having them torn away in a storm, is addressed with this design by folding them flat against the deck.

I saw the picture of them folded down. They are still a good 20 feet higher than the deck.

So they can clear bridges.

The keel issue, at least, can be solved by using a kite instead of a sail.

There appears to be at least one company working on this: https://www.cnn.com/2023/06/30/travel/airseas-giant-kites-sh...

But does the overall cost of these 'WindWings' recoup over the lifetime of cargo ship. Including the fact that they can now carry less cargo per trip. And the trip might take longer due to 'route optimizations'. Insurance is probably also going to be higher now that you have giant sails on top of the ships that makes it both more expensive but also i suspect less safe in rough seas(even when folded).

I feel that is the only true measure otherwise cargo ship builders are not inclined to build more of these.

3.3 tons of fuel per day adds up to a lot of extra cargo that isn't fuel.

A lot of these ships carry upwards of 150000 tons of cargo. Not sure if an extra 60-70 tons (assuming a 20 day trip) of cargo would be very meaningful. A quick google suggests that would only be 2 or 3 additional shipping containers.

I guess the question is how much space would the sails take.

You don't need to compare to the size of the ship, you need to compare to the size / mass / cost of the sails.

There’s also the cost of the fuel. Can’t be cheap.

That's approximately two Honda Civics.

The fuel is around the bottom hull of the ship. It provides good stability to the ship. As you use fuel you'll often take on sea water as ballast to regain the lost stability and to maintain your draft.

These are not simple machines.

That is because of the difference in mass over the voyage, the less delta in your fuel math the less of a problem it is. Also, nothing prevents you from doing exactly this with a smaller amount of fuel. Last I checked dense liquids continue to be dense liquids and will flow to the lowest point.

Do they use separate tanks or does the water go into empty fuel tanks?

Seawater is initially filtered and goes into ballast tanks that have very special yearly inspection and cleaning procedures. If you just go into a chamber that has been empty/full of seawater for a couple months you can drop dead because of CO2 buildup (or some rusting processes that eat up oxygen). Credit to sailor(s) who post about things like that on hejto.pl.

It's even more fun with clean water tanks (painting and cleaning, specific concentration of chlorine for a day plus taking samples and eventually more chlorine before flushing).

Might be slightly inaccurate as I'm writing from memory.

> If you just go into a chamber that has been empty/full of seawater for a couple months you can drop dead because of CO2 buildup (or some rusting processes that eat up oxygen)

And deadly hydrogen sulfide. "Hydrogen Sulphide can be found in tank sediment as a result of decomposing sea life which may enter the tank[.]"

https://www.imca-int.com/safety-events/crew-member-fainted-a...

Can confirm that sea water corrodes everything. I used to live on an island and we joked that it even corroded plastic. In practise it was the UV that killed all plastic, while the sea water ate all the metals, including stainless steel.

Bold words from a nanomachine hivemind that thinks 21% corrosive oxygen is normal. :p

The first climate catastrophe :-D or as Bob Ross would put it, a happy little accident.

> But does the overall cost of these 'WindWings' recoup over the lifetime of cargo ship.

Well... 1 ton of bunker fuel costs about 650 dollars, so you're looking at 7.5k saved each day, or 150k per trip (assuming an average of 20 days at sea). Cargo ships have ridiculous life expectancies measured in decades, so it's very likely to make a significant dent.

[1] https://www.statista.com/statistics/1109263/monthly-vlsfo-bu...

Cargo ships cost $100 million or thereabout, and operate for at least 30 years. Estimating that about 1/3'rd of that is time where these would be useful, this would save about $27 million and the savings grow with inflation, so that's no small change.

> savings grow with inflation

Wat?

If you're saving a $1 in fuel today, then in ten years doing the same thing you'll save more than $1 because fuel will cost more.

I'm not sure it's a useful characterization, since inflation affects everything, but it's not wrong.

Cargo ships have ridiculous life expectancies measured in decades, so it's very likely to make a significant dent.

Note that 12 tons/day was the best case, the average was 3 tons, so that's more like $2000/day or around $400K/year assuming the ship is at sea 200 days/year.

Anything on a ship with moving parts has significant maintenance costs, so it'd be nice if they had a ballpark figure of the installation/maintenance costs as well as expected lifetime of the system.

And what happens in a serious storm? It looks like these can be rotated but not folded down flat, so what happens in unpredictable winds during a storm?

They do fold flat [1]. [1] https://youtu.be/AB7cLkSVmJA

Oh that's cool, in the photo in the article they looked too tall to lay flat without interfering with each other.

The calculation is perverted by the free externalities of dumping carbon in the atmosphere, a very expensive discount. I know it's not news, but it perverts economic decisions.

The problem is that while that has no dollar value attached, the companies dont care.

It would be good if there was some global carbon tax that required equivilent carbon biomass be grown from scratch to offset emmisions. Said biomass could the be processed and stored.

Its not really a tax, its taking responsibility for the waste you produce.

Same goes for plastics. If a plastic is used in manufacturing in a way that means its going to get thrown oit eventually then that company should be responsible for collecting that amount of that said plastic from garbage and storing it long term.

This would hopefully drive people to the most efficient solutions. Some fossil fues and plastics would still be used but their negitive effects would be offset by the collection and storage process.

Right, that's what I mean by externalities.

Surprisingly, these appear to be rigid foils (hence WindWing) instead of Flettner rotors.

What I don't understand is why they didn't use normal sails instead. The sails could have a much larger area and a thinner mast would create less problems for docking, or it could even be a telescopic cilinder, able to be retracted below deck.

My guess is that the WindWing requires much less labor. Even by the standards of the 1700s and earlier, working on a sailing ship had a reputation for being dangerous work that chews through sailors, and kidnapping people and not letting them leave the ship was a common way to "recruit" sailors. These days, when kidnapping is no longer in the Overton window, and even unskilled workers have more options than the workers of the 1700s had, it would be cost prohibitive to staff these sailing ships you propose, I am guessing.

No need to pull the ropes manually. We have motors now.

https://www.yachtingmonthly.com/sailing-skills/mainsail-furl...

https://solar.lowtechmagazine.com/2009/04/sailing-at-the-tou...

I know. Still.

Likely a mechanical system offers more predictability and longevity compared to fabric.

Two reasons:

First, solid wings are dramatically better in lift drag ratio.

They start out around 3x better per square meter than conventional sails on a bermuda rig, and can get up to 7x better with careful design. This is why the America's Cup boats with wings are dramatically faster than conventional rigs (the other reason being foils).

Second, the simplicity of the rig.

These designs are self trimming, which means there's a control flap you set, and that causes the wing to have a consistent angle of attack vs the wind. As the wind vector shifts around the sail just tracks it without needing any active control or electronics. You only have to change the control flap when the bow or stern crosses the wind during a turn.

If you get into severe weather you just put the control flap in neutral and the wing just acts like a weather vane. Surprisingly enough a feathered wing like this has less drag than a bare cylindrical mast with no sail lifted. Aerodynamics can be counterintuitive.

That's what's so cool about this technology. It really is just a bolt on.

> solid wings are dramatically better in lift drag ratio

Why has anyone used fabric sails? If they could build a wooden boat, they could have made wooden sails. Too heavy, and thus modern strength/weight materials were needed?

Weight and the fact that wings are a modern invention that requires an understanding of aerodynamics

Yes, people 200 years ago did not possess the material science knowledge to build a solid wing that would not be insanely heavy, vs... canvas.

My thought exactly. Some university should build a wing sail ship using exclusively materials and tools available during the Golden age of sail.

That's a tall ask but I think something is possible. The best approach imo would be a "soft wingsail" made from two fabric sails that sandwich a central mast with ability to pivot widely if not freespin. There's some companies today chasing this as a middle ground. It's not as efficient as a solid wing, but sailors are understandably conservative and like something fabric they can take down in high winds vs let weathervane, even if the physics of the latter work out.

How would that differ from a lateen sail?

It would have battens to create an airfoil. Lateen vs burmuda is beside the point.

Here's an example of what I'm talking about: https://www.omerwingsail.com/

> Lateen vs burmuda is beside the point.

I was thinking of fore-and-aft (which I should have said instead of lateen specifically) compared with square, but my knowledge is pretty limited.

In addition to what others are saying, look at the sails of giant ships of the past. They're just big rectangles that block the wind, they don't work anything like a wing.

Look up fore-and-aft sails and lateen sails, which seem winglike (but I'm not sure of the actual aerodynamics).

I wonder how well they hold up in strong storms, or if they can be folded away for safety.

This was exactly my thought. We've all seen videos of giant ships caught in storms with green water splashing over the bow and are amazed they're able to stay afloat. Just from a glance at these sails, it looks like it would capsize the ship under in minutes in a decent storm. I would think either they fold down or they have to plan their routes very carefully to avoid bad weather.

And who says you can’t reinvent the wheel?

From the article: "Pyxis Ocean reportedly saved an average of 3.3 tons of fuel each day."

Why don’t sailboats use these?

Some really high end racing sailboats do use rigid "sails". But there's a lot to be said for a wind surface that can stow away. I assume regular sails are lighter. Also, of course, momentum and habit.

There are those who do.

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

Apart from being complex and expensive, you can't reduce their size for hard winds.

Rigid sails seems very inconvenient to fold too.

expense, weight, and lack of flexibility.

A fabric sail can easily be reduced in size by lowering it partially when the conditions call for it.

Weight aloft must be counterbalanced in the keel in a monohull. A solid sail requires heavier supports than a fabric sail.

Expense. A fabric sail can actually make a pretty good airfoil, rigidity adds an insane amount of expense to get you a level of performance that doesn't really matter to most.

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