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Comment by barbegal | Hacker News Reader

The headline is misleading they haven't put anything on a cargo ship yet and likely never will. They have a single prototype yacht which can be seen in this image https://cdn.trendhunterstatic.com/phpthumbnails/454/454358/4...

It's an interesting concept but I can't really see how it scales to large ships. To propel a larger ship you need a huge amount of force which requires a very sturdy mast and stays (guys) which support the mast. Without those elements the amount of force that can be transmitted will be negligible.

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I don't think the aim is to replace motor power completely, but to offload some of the effort for long distances to reduce fuel consumption.

As regard stays, the stay needs to be at 90deg to the sail orientation. Presumably mounted on some kind of circular track to rotate with the sail.

The engineering is challenging but not inconceivable.

the safety side of things is also interesting, it provides a secondary moving force in case something happens with the ICE part

The article says there are 15 in operation with 5 more coming in the next year. I couldn’t find details on those ships but the MV Afros is a working cargo ship outfitted with wind assistive technology.

https://www.nytimes.com/2021/06/24/magazine/cargo-ships-emis...

The 15 in operation are not the puffy sails that the headline is talking about. They are a rotor design by a different manufacturer. The rotor style sails can save about 10 to 20% of a ship's fuel https://theicct.org/sites/default/files/publications/Rotors_...

that's a great paper! I love that it walks the reader through the math! I wish more did that! I often feel papers I read are just a little outside my abilities, but this one actually makes a person smarter!

I think most papers do this mostly to prevent too much scrutiny of their calculations. Publish or perish etc

Informative video on how it works [1]. Btw the 20% is an overly optimistic scenario.

[1] https://youtu.be/JhAlWHSez90

Found this awesome simple demonstration of Flettner rotors.[1]

One question I have is, how would this work with a sort of semi-circle fan version, where the blades retract when they start getting pushed into the wind. This could theoretically have the rotor turn off of just wind power instead of external power. Here's a crude drawing lol [2].

[1] https://www.youtube.com/watch?v=XsGin7CFaF8

[2] http://draw.to/D47BxHT

This demand is significantly lower for rotating mast. On fixed mast we need shrouds to compensate side force. We also need deep massive fin to compensate overturning moment.

Look at Maltese Falcon rotating mast. They don't have any shrouds, although they are carbon fiber made.

Agree on the potential scaling issues but the article suggests it operates different from a normal sail

more of how an airplane wing generates lift (bernoulli's principle) then catching wind.

I'm just learning sailing but I believe traditional sails act like wings/airfoils as well, at least for part of the thrust.

Normal sails also generate lift, which constitutes most of the thrust. Without it, it would be impossible to sail up wind.

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

"The company plans to test the technology on a commercial freighter in 2022."

> which requires a very sturdy mast and stays (guys) which support the mast.

Did we read the same article? I read that the system was completely autonomous at the press of a button and automatically retracted in bad weather and for bridges

I think GP is asserting that that part of the article is bullshit as it regards larger craft.

The GP thinks that his large engineering expertise regarding sails after reading a wikipedia article and some press releases makes him better than Michelin - a company whose small achievements includes inventing the radial tire - into predicting what will happen in the industry and the design of inflatable structures based on a misreading of the linked article.

That's Hacker News at its finest.

Even the rendering image in the article is on a oil tanker, not cargo ship.

Tankers are cargo ships.

It is clearly a bulk carrier as it ha large visible hatches, hatches used to reach the bulk cargo.

Oil is simply liquid cargo.

What makes you think they haven't accounted for the mast engineering requirements?

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