Wing Sails on modern ships

[Astronuc]

A new sail design for cargo ships is propelling the maritime industry to a more sustainable future
https://www.businessinsider.com/sc/...shing-the-maritime-industry-to-sustainability

WISAMO from Michelin — its name is a combination of the words wing, sail, and mobility — is an inflatable, retractable, and automated wing sail. While it's not intended to replace ships' engines entirely, it lightens their loads and decreases their dependence on fuel. According to Michelin, the company that manufactured the design, the goal is to cut carbon emissions by up to 20% for existing ships and up to 50% for newly-built models.

I expect the sails and mast would have to be retractable in order for the ship to pass under some bridges, or they will be restricted from some harbors, or they will be limited in height above the sea level.

The Francis Scott Key bridge had a clearance of 185 feet (56.3 m).

Golden Gate Bridge has a clearance of 220 feet (67 m) and the Verrzano Narrows Bridge has a clearance of 228 feet (69.5 m).

Apparently, the mast(s) will be retractable.
https://wisamo.michelin.com/

https://www.yachtingworld.com/micro...ld-revolutionise-the-shipping-industry-140908

 

[Baluncore]

Michelin is into blowing things up, and inflatables.
Remember the Michelin man, AKA, Monsieur Bibendum ?

 

[DaveC426913]

Apparently, the mast(s) will be retractable.

And as an added bonus, they can play the most popular accordian music hits of the day to entertain and amuse the kids.

 

[Flyboy]

Hmmm. Not sure how useful these would be on container ships. Bulk freighters, sure, but anything without a clear-ish flat deck is kinda out of the question.

 

[DaveC426913]

Hmmm. Not sure how useful these would be on container ships. Bulk freighters, sure, but anything without a clear-ish flat deck is kinda out of the question.

Don't see why. As long as the sails can clear the top containers it should be fine.

 

[Baluncore]

Don't see why. As long as the sails can clear the top containers it should be fine.

If the masts and sails are mounted too high, such as on a container ship, vessel stability will be compromised beyond the design specifications. It will need to be a new design hull, one that sacrifices deck load for fuel economy, one with reliable fast ballast transfer between sides, to keep the hull vertical while sailing.

 

[DaveC426913]

If the masts and sails are mounted too high, such as on a container ship, vessel stability will be compromised beyond the design specifications. It will need to be a new design hull, one that sacrifices deck load for fuel economy, one with reliable fast ballast transfer between sides, to keep the hull vertical while sailing.

True. But that's just another engineering challenge that applies to any ship with high freeboard (i.e. it doesn't categorically target container ships).

And they have other ways of mitigating heel.

 

[Baluncore]

The problem is that the heel moment, is being applied with a long lever arm on a container ship. They are already operating at the stability limit, just within the profile of the canal width and depth, and the bridge and crane clearance.

Sails, will not happen to big container ships.

 

[Lnewqban]

Some more details into inflatable sails for small boats:
http://inflatedwingsails.com/en/concept/

 

[Hornbein]

A new sail design for cargo ships is propelling the maritime industry to a more sustainable future
https://www.businessinsider.com/sc/...shing-the-maritime-industry-to-sustainability



I expect the sails and mast would have to be retractable in order for the ship to pass under some bridges, or they will be restricted from some harbors, or they will be limited in height above the sea level.

The Francis Scott Key bridge had a clearance of 185 feet (56.3 m).

Golden Gate Bridge has a clearance of 220 feet (67 m) and the Verrzano Narrows Bridge has a clearance of 228 feet (69.5 m).

Apparently, the mast(s) will be retractable.
https://wisamo.michelin.com/

https://www.yachtingworld.com/micro...ld-revolutionise-the-shipping-industry-140908

From the article

the IWS inflates via an integrated air compressor to a surprisingly low pressure, just two millibars.

It creates a soft, symmetric wingsail with many of the efficiency advantages of a hard wingsail (amply demonstrated in America’s Cup and SailGP racing) but none of the problems – it’s very simple to raise and lower, and just disappears down to the deck when you don’t need it.

 

[Baluncore]

Two pascals, is the ram air pressure at about 6 kph.
I expect one side of the leading edge of the sail will then collapse inwards.
There are things we are not being told.

 

[DrJohn]

Two pascals, is the ram air pressure at about 6 kph.
I expect one side of the leading edge of the sail will then collapse inwards.
There are things we are not being told.

And yet there are ships and yachts out there using these sails, according to the articles mentioned in the earlier posts. So is it all a big conspiracy, do you think?

 

[Baluncore]

And yet there are ships and yachts out there using these sails, according to the articles mentioned in the earlier posts. So is it all a big conspiracy, do you think?

There are no big vessels using the system. There is one small demo vessel on Lake Geneva? There are many more artists impressions.

Tension in the sail fabric comes from internal pressure and mast extension. There seem to be "floors" or "decks" with apertures, built into the sail, that control the profile.

It seems to me that the dynamic external pressures on the sail, must be less than the internal pressure. Maybe 2 Pa is the minimum without wind, and it is increased by higher wind pressures through the front inlet duct, boosted by the fan. But then the entire volume must be under a pressure greater than the maximum external pressure.

I do not see a big conspiracy, just a lack of solid information in the stream of publicity.

We have seen many revolutions before, that never materialised, that could be applied to a niche application, that were then forgotten.

Screw propulsion worked out in the end, and so displaced sail.

Flettner rotor ships are still not moving significant cargo after 100 years of evaluation.
https://en.wikipedia.org/wiki/Rotor_ship#Modern_vessels

 

[Arjan82]

Two pascals, is the ram air pressure at about 6 kph.
I expect one side of the leading edge of the sail will then collapse inwards.
There are things we are not being told.

It said 2 millibars, 2 millibars is 200 Pascals...

 

[Flyboy]

That’s still not a lot of pressure. Even at 20mBar that’s probably not enough for it to support itself against wind loads.

 

[Baluncore]

It said 2 millibars, 2 millibars is 200 Pascals...

The 2 Pa I used, came from a diagram in a side linked reference, I will look for it again.
Meanwhile, the 2 mbar comes originally from a contradiction ...
https://www.yachtingworld.com/extraordinary-boats/inflated-wing-sail-121282
"2 millibars, around 1.5 grams/cm2".
1.5 g/cm2 = 0.0015 kg/cm2 = 15 kg/m2 = 15 Pa.
2 mb = 0.002 bar = 200 Pa.

 

[Frabjous]

This week’s Economist has an article about sails.
https://www.economist.com/science-and-technology/2024/05/21/a-new-age-of-sail-begins

 

[sophiecentaur]

And they have other ways of mitigating heel.

Yes but doesn't the ship need to be moving through the water?

So is it all a big conspiracy, do you think?

Not necessariiy a conspiracy - just an awareness that, in engineering, things don't always scale conveniently. Ships have got bigger and bigger because of the economics of fuel use. Large ships have their own disadvantages and (I am not a true believer) it may be that smaller sail assisted ships could be useful.
Modern racing yachts are really bad value though!

 

[Flyboy]

Large ships have their own disadvantages and (I am not a true believer) it may be that smaller sail assisted ships could be useful.

I recall seeing more than a few projects recently to build new sailing freighters. They’re pretty small and are being used for stuff like “fair trade, organic, eco-conscious coffee” or something like that, but at that smaller scale, they’re proving to be viable.

I also seem to recall seeing at least one group trying to build a small container-carrying ship with a heavy emphasis on sail power, with a capacity in the low hundreds of TEUs, but I don’t remember what happened to that project.

 

[Arjan82]

There is a lot happening in the field for wind assist ships at commercial scale:

There are several attempts for commercialization:
https://www.bbc.com/news/technology-66543643
https://www.econowind.nl/
https://bound4blue.com/
http://www.dealfeng.com/

There are research initiatives with participants actually building these ships:
https://www.marin.nl/en/jips/wisp-2

There are consultants specialized in the field:
https://bluewaspmarine.com/
https://www.finoceanltd.com/wind-assisted-propulsion/

Associations:
https://www.wind-ship.org/en/grid-homepage/

So it goes far beyond 'fair trade, organic, eco-conscious coffee'.

 

[Flyboy]

I was throwing out the coffee thing because that was the only example of purely sail powered freight I could remember. As an assist, yeah, there’s much more traction.

 

[DaveC426913]

Yes but doesn't the ship need to be moving through the water?

That is ... generally how ships work, yes.

 

[Arjan82]

I was throwing out the coffee thing because that was the only example of purely sail powered freight I could remember. As an assist, yeah, there’s much more traction.

Yeah, purely sail powered is not gonna fly, I agree with that. There is indeed some over ambitious, economically naive and ridiculously fantastical things going on there...

 

[sophiecentaur]

That is ... generally how ships work, yes.

But a ship needs to have protection from gusts of wind when it is going slowly or when the engines fail (which is the issue in this thread. Stabilisers on container ships are to protect rolling forces on deck cargo. The effect on a sail is additional; more lateral forces. A sailing yacht has a massive keel, well below water level and can heel to a ridiculous degree but still recover. That's not like a container ship with so much mass high up.

The amount of active stabilisation needed with sails would surely be a lot higher, which would have knock-ons for the overall design. You'd need to show that the stabilisation would be adequate under all conditions to make it safe and worthwhile. Beyond our pay grade, I reckon.

If the sailing mode could be de-activated quickly and easily then stability might not be so much of a problem - of course. But then, what proportion of a voyage would benefit from wind power?

 

[Arjan82]

But a ship needs to have protection from gusts of wind when it is going slowly or when the engines fail (which is the issue in this thread. Stabilisers on container ships are to protect rolling forces on deck cargo. The effect on a sail is additional; more lateral forces. A sailing yacht has a massive keel, well below water level and can heel to a ridiculous degree but still recover. That's not like a container ship with so much mass high up.

The amount of active stabilisation needed with sails would surely be a lot higher, which would have knock-ons for the overall design. You'd need to show that the stabilisation would be adequate under all conditions to make it safe and worthwhile. Beyond our pay grade, I reckon.

If the sailing mode could be de-activated quickly and easily then stability might not be so much of a problem - of course. But then, what proportion of a voyage would benefit from wind power?

I think you are underestimating how stable a flat bottomed ship actually is, just as an example, this is fine:

These ships have no keel, to be clear.

Also, the height of the center of mass isn't as high as it looks. That there is a lot of volume high up doesn't mean the mass is as well. I don't think stability is much of an issue.

 

[DaveC426913]

If the sailing mode could be de-activated quickly and easily then stability might not be so much of a problem

It is a simple matter of releasing the tension so that it points into the wind. As soon as you do that, all lift - and heel - disappears. In fact, you can do this continually as conditions change. Simply incrementally ease and harden the sail in real-time to optimize the balance between lift and heel. Decide that 15 degrees is your maximum cruising heel? Just harden up the sail, gaining lift, until heel is 15 degrees. Adjust to-taste as winds change.

 

[Baluncore]

I think you are underestimating how stable a flat bottomed ship actually is, just as an example, this is fine:

These ships have no keel, to be clear.

But each of those boats has two leeboards, the high side is showing, while the lower leeboard is deep in the water, under the vessel.
Those hulls are not loaded with cargo, and are not flat-bottomed when sailing unladen in that heeled mode, they are taking advantage of the chine and one leeboard as a keel, to minimise section, to gain speed. If they were loaded, there would be no freeboard, and they would have to limit the heel to a couple of degrees.
https://en.wikipedia.org/wiki/Leeboard

 

[Arjan82]

A leeboard does nothing for stability, if anything they decrease it because together with the sail they form the heeling moment. Removing the leeboard actually reduces the heeling moment because the lateral resistance point moves upward (although I wouldn't use that as a method to prevent capizing...). The leeboard is only there to prevent leeward motion (sideway motion, drift) The chine technically does as well, although the soft chine in this case does a lot less to prevent this.

These ships are 'form stable'. I'm unsure of this translation to English, Dutch is 'vormstabiel':

Left picture is 'form stable' typical for the flat-bottomed ships I showed in the picture, as for most merchant ships. Here the center of gravity is higher than the center of buoyancy. Right is 'weight stable' (again, unsure of the translation), typical for yachts, where this is reversed.

Cargo actually makes the ship much more stable since the righting moment becomes much larger for equal heel. The total heel they can have may be somewhat less if you have less freeboard, but sea-going ships have a high freeboard anyway, that's not going to be a limitation there.

 

[Rive]

just as an example, this is fine:

For those small boats. But as far as I know for big cargo ships: cargo placement, loading and even unloading is supposed to go with plans/limits regarding stability and so the acceptable amount of cargo (profit to be made) to be loaded will depend on stability budget => it's just acceptable, not much margin left.

Ps.: from a different point of view: you might spend by the reduced cargo what you get with the sail.

 

[sophiecentaur]

It is a simple matter of releasing the tension so that it points into the wind. As soon as you do that, all lift - and heel - disappears. In fact, you can do this continually as conditions change. Simply incrementally ease and harden the sail in real-time to optimize the balance between lift and heel. Decide that 15 degrees is your maximum cruising heel? Just harden up the sail, gaining lift, until heel is 15 degrees. Adjust to-taste as winds change.

That's what I learned in my first hour of sailing and it works in ideal conditions. A craft of the size and cost that is described in this thread won't react fast - you can't just let the mainsheet fly when a sudden squall turns up (except in a small dinghy and I never used them much). With a container ship you already have a scary amount of windage which it there all the time and will have the full force from any beam wind.

you might spend by the reduced cargo what you get with the sail.

Exactly. You cannot ignore the reason that the ships are out there in the first place.
There are occasions when the wind is just right and you can get your percent saving in fuel costs and that's good. It's liked the old days of sail when wind and tide totally governed where you could go. A modern container ship has a hull that's not designed to sail so similar constraints will apply. Only half the trips will be in the best direction for the wind and you can't deviate too far because of the extra fuel costs.

It's all down to the economics and no amount of knowledge about sailing a sailing boat is a good source for assessing this sort of project. We need to just wait to see what develops (and when the first ship is lost in a storm).

 

[Dullard]

"In fact, you can do this continually as conditions change"

Reference: https://www.physicsforums.com/threads/wing-sails-on-modern-ships.1063045/

We've obviously not sailed in the same types of thunderstorms. :)

 

[DaveC426913]

That's what I learned in my first hour of sailing and it works in ideal conditions. A craft of the size and cost that is described in this thread won't react fast - you can't just let the mainsheet fly when a sudden squall turns up (except in a small dinghy and I never used them much). With a container ship you already have a scary amount of windage which it there all the time and will have the full force from any beam wind.

I think you're sort of over-working the sailing analogy. This isn't a sailboat, subject to the whims of the seas. It's a fully-functional container ship, under power, with very sophisticated radar, that just happens to have an additional passive propulsion source whose sole function is to reduce fuel consumption.

You deploy the sail when conditions are right. You are still under power, just getting an assist. Unpredictable winds are dealt with by "luffing" the sails as-needed. No squalls are going to sneak up on you with your radar. Even if winds build precipitously, you're still not a sailboat, worrying about the whims of a rising gale - you're a container ship, under power, built for this. You simply depower the sails (first by "luffing" - which takes two seconds, and then by retracting) and continue steaming under full control.

 

[gleem]

Cargill launched the sail-augmented bulk carrier Pyxis last August on a six-month test cruise saving on average 3 tons of fuel per day with only two sails. Is it worth it?

 

[Dullard]

In case you were wondering:
A Panamax bulk carrier (without sails) typically burns fuel at a rate of 90 Tons/day.

 

[Baluncore]

LNG tankers will not benefit directly from sail unless they are better insulated, since they are fuelled by the LNG that boils off during the voyage.

Australia sells coal and iron ore to China for steel making. It would be more sensible to make the steel next door to the coal mine in Australia, and so not ship most of the raw material in bulk carriers. Sail-assist will further lock-in that inefficiency.