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This is how two contra-rotating propellers can make ships more energy efficient

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This is how two contra-rotating propellers can make ships more energy efficient


One of the setups investigated in the Sea Zero project was a combination of contra-rotating propellers (the red propellers in the middle of the picture) and two pulling thrusters. A pulling thruster acts as a propeller that pulls the ship forward, much like an aircraft propeller. Credit: Brunvoll

By using two propellers that rotate in opposite directions, a ship can use less energy to move forward. New knowledge means that more ships can use the technology, including Hurtigruten’s Sea Zero project for its coastal cruise ships.

SINTEF has now designed and manufactured new measuring equipment for model testing of contra-rotating . This could be good news for many large ships.

“We see that propulsion efficiency increases when we utilize some of the energy lost from the front propeller at the same time as the rear propeller gets better water flow. This can provide more than 10% better efficiency compared to conventional propellers,” says Øyvind Rabliås, a researcher at SINTEF.

Although contra-rotating propellers are not new, they are still rarely used on commercial ships. The reason has been their cost and more complicated design than traditional layouts. That may be changing now.

“Together with our research partners, we’ve spent a lot of time on understanding and developing solutions for this. Now we believe that the technology is mature and ready for wider use,” says Jahn Terje Johannessen. He is a senior hydrodynamicist at Brunvoll, a leading provider of propulsion and maneuvering systems.

Good test results

SINTEF’s new measurement system was developed when Hurtigruten decided to use contra-rotating propellers for its zero-emission cruise ship in the Sea Zero project. The goal is an emission-free Hurtigruten ship with a sustainable and circular solution by 2030.

Contra-rotating propellers have significantly better efficiency than today’s propeller systems.

“This design simply means that we need less energy to achieve the same speed compared to conventional propellers. Brunvoll’s design is also more efficient than the contra-rotating propellers that exist today,” says Gerry Larsson-Fedde, chief operating officer at Hurtigruten.







How the propellers spin in opposite directions during a test run in the cavitation tunnel at the Norwegian Ocean Technology Centre. Credit: Norwegian University of Science and Technology

From drawing board to reality

A broad interdisciplinary team at SINTEF Ocean, from technicians and instrumentation engineers to design experts and researchers, has developed the new measuring equipment for model testing contra-rotating propellers. Together, they arrived at a solution that is well suited for self-propulsion tests.

Two dynamometers, which are instruments used to measure force in rotating systems, have also been developed.

“One version is suitable for integrating into ship models that are tested in the Towing Tank, meaning that it is built into the model, and the other version is used in open water tests and in cavitation tests,” says Rabliås.

The system has already tested Brunvoll’s propeller system for Hurtigruten. The results provided valuable insight into the system’s performance and helped identify the most efficient propulsion solution for further development.

“It was an added bonus for Brunvoll that the project is so versatile. We have a lot of different industrially relevant issues in our work to create a demonstrator,” says Johannessen.

This is how two contra-rotating propellers can make ships more energy efficient
Model of Hurtigruten’s new cruise ship in Sea Zero during testing in the ocean basin. Credit: SINTEF

Hurtigruten is also very pleased to have its ground-breaking ship tested.

“It’s fantastic for us that we can test all the parts of the Sea Zero design at such a professional and advanced laboratory as SINTEF has. Contra-rotating propellers are new to us, and they are not common on ships either. That’s why it is so important for us to be able to thoroughly test the ship design in the cavitation tunnel. Then we’ll know that it will work in practice,” says Larsson-Fedde.

Some challenges too

Propulsion efficiency is increased by recovering part of the energy loss from the front propeller and by better inflow to the rear propeller. That is why it is possible to achieve more than a 10% increase compared to conventional propellers. However, contra-rotating propellers require a complex shaft-in-shaft system.

“The design process is also more complicated than for conventional propellers, both because of complex flow phenomena and the larger number of parameters that need to be adjusted, compared to one propeller. This applies to both the diameter ratio and the propeller’s revolution ratio between the two propellers, for example,” says Rabliås.

It will be exciting to follow the developments in the future for Hurtigruten as well.

“The goal of Sea Zero is to design the world’s most energy-efficient ship, and in that quest we have to leave no stone unturned. The propulsion itself uses a lot of energy, and so contra-rotating propellers are very exciting for us to look at,” says Larsson-Fedde.

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This is how two contra-rotating propellers can make ships more energy efficient (2025, November 10)
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The Best Babbel Promo Codes and Deals for April 2026

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The Best Babbel Promo Codes and Deals for April 2026


I’ve been trying to become fluent in Spanish for the last decade. After spending most of my adult life surrounded by multilinguals, I often feel like I’m playing an impossible game of catch-up. Like everyone else, I’ve tried to become regimented with practicing on an in-phone app like Duolingo, which attempts to ‘game-ify’ language learning, but mostly ends up with a sad and sick-looking green bird icon guilting me to practice every time I open up my phone.

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Unlock Your Babbel Promo Code and Save Big in April 2026

Not only is Babbel a helpful interactive app to simplify language learning, but it also has holistic services to help introduce the language to every part of your life. These are things like Babbel videos, which do a deep dive into what makes a language so fascinating, Babbel podcasts, which are led by Babbel experts who take an inside look at local culture and break down language secrets, and Babbel magazine, which highlights stories from around the world so you can better understand the history, culture, and people from the language you’re learning (and maybe will inspire you to take a trip to practice that language IRL!).

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As stated, knowing another language is an invaluable life skill, and a skill that is immeasurably valuable to healthcare workers, who may be able to more easily give lifesaving care. Healthcare professionals and nurses get a Babbel discount of 60% off a six-month Babbel subscription. To claim the Babbel discount, users just need to verify their medical credentials via ID.me.

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This Babbel discount also applies to active duty military, veterans, and their families, who are also eligible for 60% off six-month Babbel subscriptions. This Babbel military coupon is valid for National Guard, reserve members, and immediate family members of service personnel, and all you need to do is verify your status at ID.me.

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Grab Top Lifetime Subscription Deals and Save in April 2026

Everyone knows that learning a language is a lifetime process, and Babbel wants to make it even easier for you to commit to it. If you pay once, you’ll get access to all available Babbel languages forever with Lifetime deals. You’ll just need to look for the “Lifetime Subscription” Babbel promos that could potentially save you hundreds of dollars over several years. Be sure to check back often, as these rotating deals often pop up during major holiday sales. While the upfront cost is higher, you’ll get access to all 14 available languages with this Babbel promo code lifetime subscription deal.



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Robotaxi Outage in China Leaves Passengers Stranded on Highways

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Robotaxi Outage in China Leaves Passengers Stranded on Highways


An unknown technical problem caused a number of robotaxis owned by the Chinese tech giant Baidu to freeze on Tuesday in the middle of traffic, trapping some passengers in the vehicles for more than an hour.

In Wuhan, a city in central China where Baidu has deployed hundreds of its Apollo Go self-driving taxis, people on Chinese social media reported witnessing the cars suddenly malfunction and stop operating. Photos and videos shared online show the Baidu cars halted on busy highways, often in the fast lane.

A college student in Wuhan tells WIRED that she was stuck in a Baidu robotaxi with two friends for about 90 minutes on Tuesday. (She asked to be only identified with her last name, He, to protect her privacy.) The student says the car malfunctioned and stopped four or five times during the trip before it eventually parked in front of an intersection in eastern Wuhan. Luckily, it was not a busy road, and the group was not in immediate danger. The screen display in the car asked the passengers to remain in the car with seatbelt on and wait for a company representative to come “in five minutes,” according to a photo He shared with WIRED.

He says it took about 30 minutes to reach a Baidu customer representative on the phone. “They kept saying it would be reported to their superior. But they didn’t explain what caused [the outage] or let us know how long we needed to wait for the staff to come,” He says. But no one ever came, and after another hour of waiting, the three passengers decided to just get out and go home by themselves (the doors weren’t locked).

On Chinese social media, other passengers also complained about being unable to reach Baidu’s customer support. “I tried every way I could think of to call for help using the options the app showed, but the phone line wouldn’t go through, and when I pressed the SOS button it told me it was unavailable. So then what exactly is the SOS for?” wrote one person in a post on RedNote alongside a video showing the button not working. She said she had to force the door to open and get out of the car as traffic halted to a complete stop behind her robotaxi. “Apollo Go, you really owe me an apology,” she wrote.

Baidu didn’t immediately respond to a request for comment. Local police in Wuhan issued a statement around midnight in China that said the situation was “likely caused by a system malfunction,” but the incident is still under investigation. No one was injured and all passengers have exited the vehicles, the police added. It’s unclear how many of Baidu’s robotaxis may have been impacted.

One dash cam recording posted to RedNote shows a car passing 16 Apollo Go vehicles parked on the road in the span of 90 minutes. On several occasions, the video shows the driver narrowly avoiding hitting the robotaxis by braking or changing lanes at the last minute.

Others were apparently not as fortunate. In another RedNote post, a man claimed he crashed into one of the malfunctioning Baidu vehicles. The man wrote in the caption that he was driving over 40 mph on a highway when the car in front of him suddenly changed lanes to avoid the stopped robotaxi. He couldn’t react fast enough and ended up running into the self-driving car. Photos of the man’s orange SUV being towed away show that the car’s front-right fender was completely torn off, and other parts appeared to have sustained major damage.



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Our Favorite Affordable Air Purifier Is Temporarily Even Cheaper

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Our Favorite Affordable Air Purifier Is Temporarily Even Cheaper


Tired of the stale, fetid air looming over your apartment like a cloud? Check out the Coway Airmega Mighty, an already wallet-friendly home air purifier that’s even cheaper right now as part of the Amazon Big Spring Sale. It’s currently marked down to just $154, a $76 discount from its typical price, but you’ll want to move quickly if you’re interested, as the deal is only available for a limited time.

Coway

Airmega Mighty AP-1512HH

Despite its low price tag and squat stature, the Airmega Mighty is capable of cleaning a substantial amount of space. At full bore, it can handle a 361-square-foot space, although you’ll get the best performance, and save your ears, if you’re closer to a 200-square-foot room. If you don’t want it running constantly, there are built-in timers to automatically shut off after 1, 4, or 8 hours, or you can use Eco Mode, which will run until the Might doesn’t sense any dirty air for half an hour.

That’s right, the Airmega Mighty has a built-in air quality sensor, and it reflects the current state of the air quality using a colored light with three levels. It uses those readings to automatically adjust the fan speed and timing settings on the fly, as well as giving you a peak into how bad the air you’re breathing right now is for you. While it lacks integration with smart home setups like Google Home, it makes up for it by handling all of its own business without Wi-Fi or extra apps on your phone.

While the Coway Airmega Mighty is available in three colors, only the black and silver model is currently discounted, so you’ll have to pay full price if it doesn’t match your living room’s color scheme. We’ve put in the work testing every air purifier we could get our hands on, so make sure to check out the full guide if you’re trying to clean up your space. The Coway is discounted as part of Amazon’s Big Spring Sale, and we’ve got the best deals from products we’ve tested gathered in one place if you want to save some bucks.



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