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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 Presidents’ Day Deals on Gear We’ve Actually Tested

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The Best Presidents’ Day Deals on Gear We’ve Actually Tested


Presidents’ Day Deals have officially landed, and there’s a lot of stuff to sift through. We cross-referenced our myriad buying guides and reviews to find the products we’d recommend that are actually on sale for a truly good price. We know because we checked! Find highlights below, and keep in mind that most of these deals end on February 17.

Be sure to check out our roundup of the Best Presidents’ Day Mattress Sales for discounts on beds, bedding, bed frames, and other sleep accessories. We have even more deals here for your browsing pleasure.

WIRED Featured Deals

Branch Ergonomic Chair Pro for $449 ($50 off)

  • Photograph: Julian Chokkattu

  • Photograph: Julian Chokkattu

  • Photograph: Julian Chokkattu

Branch

Ergonomic Chair Pro

The Branch Ergonomic Chair Pro is our very favorite office chair, and this price matches the lowest we tend to see outside of major shopping events like Black Friday and Cyber Monday. It’s accessibly priced compared to other chairs, and it checks all the boxes for quality, comfort, and ergonomics. Nearly every element is adjustable, so you can dial in the perfect fit, and the seven-year warranty is solid. There are 14 finishes to choose from.



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Zillow Has Gone Wild—for AI

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Zillow Has Gone Wild—for AI


This will not be a banner year for the real estate app Zillow. “We describe the home market as bouncing along the bottom,” CEO Jeremy Wacksman said in our conversation this week. Last year was dismal for the real estate market, and he expects things to improve only marginally in 2026. (If January’s historic drop in home sales is indicative, that even is overoptimistic.) “The way to think about it is that there were 4.1 million existing homes sold last year—a normal market is 5.5 to 6 million,” Wacksman says. He hastens to add that Zillow itself is doing better than the real estate industry overall. Still, its valuation is a quarter of its high-water mark in 2021. A few hours after we spoke, Wacksman announced that Zillow’s earnings had increased last quarter. Nonetheless, Zillow’s stock price fell nearly 5 percent the next day.

Wacksman does see a bright spot—AI. Like every other company in the world, generative AI presents both an opportunity and a risk to Zillow’s business. Wacksman much prefers to dwell on the upside. “We think AI is actually an ingredient rather than a threat,” he said on the earnings call. “In the last couple years, the LLM revolution has really opened all of our eyes to what’s possible,” he tells me. Zillow is integrating AI into every aspect of its business, from the way it showcases houses to having agents automate its workflow. Wacksman marvels that with Gen AI, you can search for “homes near my kid’s new school, with a fenced-in yard, under $3,000 a month.” On the other hand, his customers might wind up making those same queries on chatbots operated by OpenAI and Google, and Wacksman must figure out how to make their next step a jump to Zillow.

In its 20-year history—Zillow celebrated the anniversary this week—the company has always used AI. Wacksman, who joined in 2009 and became CEO in 2024, notes that machine learning is the engine behind those “Zestimates” that gauge a home’s worth at any given moment. Zestimates became a viral sensation that helped make the app irresistible, and sites like Zillow Gone Wild—which is also a TV show on the HGTV network—have built a business around highlighting the most intriguing or bizarre listings.

More recently, Zillow has spent billions aggressively pursuing new technology. One ongoing effort is upleveling the presentation of homes for sale. A feature called SkyTour uses an AI technology called Gaussian Splatting to turn drone footage into a 3D rendering of the property. (I love typing the words “Gassian Splatting” and can’t believe an indie band hasn’t adopted it yet.) AI also powers a feature inside Zillow’s Showcase component called Virtual Staging, which supplies homes with furniture that doesn’t really exist. There is risky ground here: Once you abandon the authenticity of an actual photo, the question arises whether you’re actually seeing a trustworthy representation of the property. “It’s important that both buyer and seller understand the line between Virtual Staging and the reality of a photo,” says Wacksman. “A virtually staged image has to be clearly watermarked and disclosed.” He says he’s confident that licensed professionals will abide by rules, but as AI becomes dominant, “we have to evolve those rules,” he says.

Right now, Zillow estimates that only a single-digit percentage of its users take advantage of these exotic display features. Particularly disappointing is a foray called Zillow Immerse, which runs on the Apple Vision Pro. Upon rollout in February 2024, Zillow called it “the future of home tours.” Note that it doesn’t claim to be the near-future. “That platform hasn’t yet come to broad consumer prominence,” says Wacksman of Apple’s underperforming innovation. “I do think that VR and AR are going to come.”

Zillow is on more solid ground using AI to make its own workforce more productive. “It’s helping us do our job better,” says Wacksman, who adds that programmers are churning out more code, customer support tasks have been automated, and design teams have shortened timelines for implementing new products. As a result, he says, Zillow has been able to keep its headcount “relatively flat.” (Zillow did cut some jobs recently, but Wacksman says that involved “a handful of folks that were not meeting a performance bar.”)



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Do Waterproof Sneakers Keep the Slosh In or Out? Let WIRED Explain

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Do Waterproof Sneakers Keep the Slosh In or Out? Let WIRED Explain


Running with wet feet, in wet socks, in wet shoes is the perfect recipe for blisters. It’s also a fast track to low morale. Nothing dampens spirits quicker than soaked socks. On ultra runs, I always carry spares. And when faced with wet, or even snowy, mid-winter miles, the lure of weatherproof shoes is strong. Anything that can stem the soggy tide is worth a go, right?

This isn’t as simple an answer as it sounds. In the past, a lot of runners—that includes me—felt waterproof shoes came with too many trade-offs, like thicker, heavier uppers that change the feel of your shoes or a tendency to run hot and sweaty. In general, weatherproof shoes are less comfortable.

But waterproofing technology has evolved, and it might be time for a rethink. Winterized shoes can now be as light as the regular models, breathability is better, and the comfort levels have improved. Brands are also starting to add extra puddle protection to some of the most popular shoes. So it’s time to ask the questions again: Just how much difference does a bit of Gore-Tex really make? Are there still trade-offs for that extra protection? And is it really worth paying the premium?

I spoke to the waterproofing pros, an elite ultra runner who has braved brutal conditions, and some expert running shoe testers. Here’s everything you need to know about waterproof running shoes in 2026. Need more information? Check out our guide to the Best Running Shoes, our guide to weatherproof fabrics, and our guide to the Best Rain Jackets.

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How Do Waterproof Running Shoes Work?

On a basic level, waterproof shoes add extra barriers between your nice dry socks and the wet world outside. If you’re running through puddles deep enough to breach your heel collars, you’re still going to get wet feet. But waterproof shoes can protect against rain, wet grass, snow, and smaller puddles.

Gore-Tex is probably the most common waterproofing tech in footwear, but it’s not the only solution in town. Some brands have proprietary tech, or you might come across alternative systems like eVent and Sympatex. That GTX stamp is definitely the one you’re most likely to encounter, so here’s how GTX works.

The water resistance comes from a layered system that is composed of a durable water repellent (DWR) coating to the uppers with an internal membrane, along with other details like taped seams, more sealed uppers with tighter woven mesh, gusseted tongues, and higher, gaiter-style heel collars.



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