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Comment by IB885588 | Hacker News Reader

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.

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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

It seems like Magnus sails work best when the wind is coming from the side (port or starboard), since the direction of force is perpendicular to the wind [0]. Doesn't matter which side, since you can just reverse the rotation of the cylinder.

With a headwind or tailwind, tacking could be used but the increased distance traveled may offset the gains from the Magnus sail.

0: https://en.wikipedia.org/wiki/Magnus_effect

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) wind power systems will help when going straight upwind.

> 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.

> In fact, the Magnus rotors will not provide any usefull thrust is both upwind and downwind scenarios.

If the wind is coming from behind won't it simply push the stationary cylinder, adding some thrust?

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

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

I remember seeing this years ago. Wonder why it hasn't taken off. If their videos are honest in the ease of operation it looks like a great idea.

Hydrogen fuel cells are looking likely. Solar will probably produce too much electricity for usage during the day, so use that spare energy to split water to create Hydrogen fuel.

I was curious how much sense this actually made so I did the math, sources at the bottom. I suspect my sources aren't perfect, but they're probably close enough to get an idea of things.

Our hypothetical container ship is roughly 400m x 59m, or 23600 m^2, and solar panels generate ~4.5 kWh/m^2 after inefficiencies, giving a total energy generated of 106.2 megawatt hours per day for a ship, if you had a big solar array above all the containers. Assuming an 85% efficient hydrogen fuel cell, that gives you losses both in storing and reclaiming electricity from that storage process. Assuming 1/3 of your energy can be used while generating it and the other 2/3 has to be stored as Hydrogen and then spent to power the energy, losing energy both ways, that leaves you an effective ~81 MWh/day.

Meanwhile the existing engines on that same container ship can currently run at about 90 MW, which means it can output more energy burning bunker fuel in one hour than our solar panels gave us in the entire day.

Container ship size: https://en.wikipedia.org/wiki/Container_ship#Size_categories Energy per day: https://www.quora.com/How-much-solar-energy-is-generated-per... Fuel cell efficiency: https://en.wikipedia.org/wiki/Fuel_cell Container ship energy usage: https://newatlas.com/shipping-pollution/11526/

Clarification: I was talking about using excess electricity from shore based solar units. This would give operators somewhere to dump excess power cheaply (preventing negative electricity rates), all while providing fuel that's easy to store and usable in applications where batteries wouldn't work.

Obviously at this point fuel cells cannot produce the power output that diesel engines can at a given weight. But your power estimates on what a hydrogen fuel cell can do are off by a bit. Some quick searching finds portable 1MW fuel cells, existing 11MW power plants, and a planned 80MW power plant that's being constructed soon in South Korea. Obviously the latter probably weight too much for a ship today, but as the weight comes down that becomes a possibility.

> But your power estimates on what a hydrogen fuel cell can do are off by a bit

My estimate didn't assume the ship left the shore with any hydrogen fuel. I (apparently incorrectly) assumed you meant that the ship would generate its own hydrogen during the day from excess solar while it was in transport.

Ah yes, that wouldn't work at all.

If solar cells got effective enough to generate that much power, you’d probably be better off with solar + battery anyhow.

Isn't hydrogen difficult to store? I've heard that it will leak out of just about everything.

You might be thinking of helium, which becomes a zero viscosity superfluid when cold enough.

Hydrogen can diffuse through certain metals and weaken them [1]. Currently, hydrogen storage is costly and tricky for a number of reasons [2]. It’s also very important to avoid leaks into enclosed areas since it’s extremely flammable.

[1]: https://en.wikipedia.org/wiki/Hydrogen_embrittlement

[2]: https://www.energy.gov/eere/fuelcells/hydrogen-storage-chall...

Oh, didn't know it'd leach into metals, that's interesting.

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