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

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

#141

Post by nattaylor »

JamesCoyne wrote: post #129

This led me to wonder how important height was a restriction on ships. Turns out "air draft" is reported for major ports. Some interesting findings: The Panama Canal has an air draft of 201 ft imposed by the Bridge of the Americas; the Port of Oakland has an air draft of 220 ft imposed by the Golden Gate Bridge. Height from waterline does not appear to be typically listed for ships, but I would guess that most cargo…

I believe the unloaded freeboard of a typical containership is 80-100' The bridge (navigation deck) is higher, but the "sails" would be mounted from the deck, so I expect most ships would be OK.

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

#142

Post by jessaustin »

jessriedel wrote: post #139
kenneth wrote: post #51

Earlier quoted context omitted.

Regular sails actually work similarly to a wing, in that pressure differentials on either side create a force we call lift on a plane, rather than simply being "pushed from the back" by directly catching the wind. That's why a sailboat can go in almost any direction regardless of which direction the wind is blowing.

Edit: sorry, nevermind, I was confused as to what you were claiming.

Reading the parent carefully, I find nothing that contradicts what you have written in response. Pressure is just force over area.

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

#143

Post by LeifCarrotson »

cwmoore wrote: post #44
LeifCarrotson wrote: post #37

Earlier quoted context omitted.

300m^2 only gets you a couple hundred kW on the brightest days at peak efficiency. These ships require powerplants providing on the order of 50,000 kW. A 40-acre floating solar farm would add a LOT of drag. Better to make the solar farm stationary, use it to synthesize fuel, and run the ship with an internal combustion engine for power density. Maybe someday batteries could be used.

I believe you. The difference between required and available power is large. Can you provide sources that derive/explain/summarize the figures you present so that others may better understand the reasoning?

Sure, sorry.

The rule-of-thumb max for solar irradiance is 1 kW/m^2 (noon, clear day, low latitude, etc):

https://en.wikipedia.org/wiki/Solar_irradiance#Irradiance_on...

The rule-of-thumb for the electric power output of a solar cell is about 20% of the irradiance.

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

And because this drops in the morning and evening and falls to zero at night, you realistically only get a bit more than 1kWh/day with a 1 m^2 solar cell.

And these ships require huge powerplants. Maersk's biggest ships use this engine:

https://en.wikipedia.org/wiki/W%C3%A4rtsil%C3%A4-Sulzer_RTA9...

which outputs over 80 MW.

No citation for the drag caused by a floating mat of solar cells. The fact that these enormous ships burn this much fuel should be evidence that dragging a much more enormous mat should show that dragging an even more enormous and more draggy mat would be a non-starter.

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

#145

Post by jabl »

nabla9 wrote: post #75

Viking Line installed similar 80-foot rotor sail on a LNG powered Cruise Ferry on the route between Helsinki-Stockholm. It reduces power usage roughly 20 percent (900 tonnes CO2 annually). Compared to tankers ferries don't carry significant amount of weight even when they are full. They are basically full of air and 60-100 cars or trucks. Together with using LNG, periodically cleaning the bottom of the ship, slower s…

> Viking Line installed similar 80-foot rotor sail on a LNG powered Cruise Ferry on the route between Helsinki-Stockholm.

Turku - Stockholm, actually.

> The best way to reduce energy consumption for a ship is to reduce the speed and make thinner ships.

Do you mean thinner as in narrower, or thinner materials to save weight? If you mean narrower, I've understood bigger ships tend to have a length/width ratio of about 6:1, as a rule of thumb compromise between seakeeping ability, fuel consumption, cargo space etc. Do you have some more information about design tradeoffs going into such narrower ships?

> New cargo ships optimized for slow speed don't have the bulbous bow because it does not increase efficiency in lower speeds.

Oh, interesting! Any links for further reading on this topic?

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

#147

Post by newnewpdro »

Calling these sails is a stretch, and IMHO just an attempt to market them as more "green" than they really are.

They may as well be propellers. It's great to improve the fuel efficiency of these vessels, but the word sail evokes a mental image profitably inconsistent with reality.

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

#148

Post by craftyguy »

qume wrote: post #120

My small 12 meter long boat has a sail area of 900sqft. When sailing perpendicular to the wind it captures pretty much all of that. The sail on that ship is 100' high, and looking at the aspect is around 15' wide, or 1500sqft. That type of sail I think only harneses half of that area, so half of 1500' or 750' best case. I can say with complete confidence that if all the energy from two of my boats were towing one of…

These use rotor sails, which are different than what you have on your boat. Unless of course you also have rotor sails?

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

#149

Post by jabl »

siruncledrew wrote: post #41
ValleyOfTheMtns wrote: post #23

I've been wondering why shipping companies haven't been doing this for years now. Whenever I brought it up with friends they would say it's probably not worth the effort, but I can't see how it wouldn't be worth it. It's essentially free energy to help move the ship around. Got to say, I feel vindicated by this story.

I think part of it is needing the technology/implementation piece. Wind power was viable for centuries, but as ships got bigger and bigger, steam/petrol engines became the standard in the shipping industry as traditional sails were no longer viable. Now that we are developing higher efficiency renewable energy technology, we have the opportunity to move full-circle back towards wind power again. However, since these…

> Wind power was viable for centuries, but as ships got bigger and bigger, steam/petrol engines became the standard in the shipping industry as traditional sails were no longer viable.

My understanding is that the main driver in the sail->steam transition was that steam ships were usually faster (and had much less variability in their schedule), and required smaller crews.

The glory of the "last windjammers" was largely enabled by very cheap labor from then-developing countries, allowing them to be competitive on a few select long distance routes.

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

#150

Post by toomim »

fmsf wrote: post #2

It's called the Flettner rotor, it uses the Magnus Effect. Cool stuff but not exactly new tech. It gives a nice read, here's some links to wikipedia on the topic: https://en.wikipedia.org/wiki/Magnus_effect and https://en.wikipedia.org/wiki/Rotor_ship I'm curious of what will be the results.

Here's a video demonstrating Flettner Rotos on a boat: https://www.youtube.com/watch?v=__8-QSXgupA
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