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 propellers. 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.

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.

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.

A team of engineers at the University of California San Diego has developed an electronic sticker that can monitor a person’s vitamin C levels using the sweat from their fingertips—no blood draws, lab visits or batteries required. The flexible sticker, which attaches to the outside of a drinking cup, collects trace amounts of sweat as a person grips the cup. Within minutes, the system harvests enough power from the sweat to analyze it for vitamin C and wirelessly sends the results to a nearby laptop.

Details about the device are published in Biosensors and Bioelectronics.

“By turning everyday objects like cups or bottles into smart sensors, people can gain real-time insights into their health and wellness without changing a thing about their daily routine,” said study co-senior author Patrick Mercier, a professor in the Department of Electrical and Computer Engineering at the UC San Diego Jacobs School of Engineering.

“We’re moving toward a future of ‘unawareables’—devices that are unobtrusive and essentially invisible so that you are unaware that you’re even using them. You just go about your day and your drinking cup can give you access to all this rich information.”

Malnutrition and micronutrient deficiencies continue to affect millions of people worldwide. While vitamin C plays a key role in immune function, tissue repair and iron absorption, testing for it currently requires blood draws, specialized laboratory equipment and costs around $50 per test in the U.S. These barriers make frequent monitoring impractical for many people.

The new sticker offers a simple, convenient and low-cost alternative. Built on a flexible, adhesive polymer sheet, the system integrates screen-printed electronic components. A porous hydrogel pad mounted on the sticker collects sweat from the fingertips. A built-in biofuel cell converts chemicals in the sweat into electricity, which powers a custom printed circuit board and the vitamin C sensor. The circuit board reads signals from the vitamin C sensor and wirelessly transmits the data via Bluetooth low energy.

“Most people only get a snapshot of their health once a year at the doctor. But our bodies change much more frequently than that,” Mercier said. “We want to make access to health data as frequent and effortless as holding your morning coffee cup or orange juice bottle.”

Another special feature of the sticker is that it generates power without requiring physical exertion from the user. Fingertips, despite their small size, are among the body’s most prolific sweat producers—each is packed with over a thousand sweat glands and can produce between 100 and 1,000 times more sweat than most other areas on the body. This steady trickle of natural perspiration provides a continuous energy source that allows the sticker to operate even when the user is at rest.

Because the system is battery-free, it can be manufactured at low cost—potentially for just a few cents per unit. Its affordability could also make future versions of the system disposable and widely accessible, particularly in low-resource areas.

The work is a collaboration between the labs of Mercier and Joseph Wang, a professor in the Aiiso Yufeng Li Family Department of Chemical and Nano Engineering at the UC San Diego Jacobs School of Engineering. It builds on wearable technologies that Wang’s lab has pioneered—including tattoo-like biochemical sensors and fingertip-power wearables—along with ultra-low power, battery-free wireless systems developed in Mercier’s lab.

In tests, the device was stuck onto a disposable drinking cup and accurately tracked changes in vitamin C levels after participants took a supplement or drank orange juice. The device powered itself for more than two hours using only sweat-derived energy.

“This is an elegant extension of our early fingertip sweat-based technology toward effortless, continuous monitoring of personal nutrition and health,” said Wang, one of the study’s co-senior authors. “By moving sensors from the skin to the surface of everyday objects like cups or bottles, we are expanding what wearable technology can be.”

The team plans to expand the technology to measure additional nutrients and biochemicals. Future versions could send readings directly to smartphones or smartwatches to provide more seamless, real-time tracking of personal health data throughout the day.

Co-authors of the study include Muhammad Inam Khan, Ryan Burns, Akshit Agarwal, Lu Yin, Jongmin Moon, Bumsik Choi, Shichao Ding and Tamoghna Saha, all at UC San Diego.

Looking for a juiced-up Bluetooth speaker that can also keep your other devices charged? The JBL Charge 6 is currently marked down to just $130 on Amazon, an impressive $70 off its usual list price.

Like other JBL Bluetooth speakers, the Charge 6 has a big, loud sound profile. It’s great for parties thanks to its bass-forward setup, and it gets loud enough for a dance party or quiet enough for an evening by the campfire. It also packs in the features we’d expect from a modern portable speaker, like Auracast, which will let you pair it with other compatible JBL speakers to form a network of sound. You can even plug it into some devices for lossless playback, if you’re craving a little more detail and nuance in your sound.

While the Charge 6 is a decent Bluetooth speaker in its own right, it also acts as a charging hub for your other devices, saving you from having to carry around two separate chunks of plastic. The USB-C port on the side can charge your phone, and it has enough juice for up to 24 hours of listening, or up to 28 hours with Playtime Boost, a JBL feature that squeezes some extra life out of a Bluetooth speaker’s battery.

It’s available in a variety of fun and exciting colors, so you don’t have to settle for just plain black or white. I spotted the same $70 discount on every in-stock color, including the vaguely hot dog-looking Pink option, and the camo-like Squad color, in case you need your speakers to hide in the woods with you. It also includes a carrying strap, and while our reviewer Ryan Waniata wasn’t enthused by the strap’s durability, it may help you lug around the comparatively heavy 3-pound speaker. It’s at least quite rugged, with an IP68 dust and water rating, one of the strongest available.

The biggest downside to the Charge 6 is its relatively high price point, so taking almost half off the purchase price makes this a much more appealing buy. If it’s a bit too big for your lifestyle, make sure to swing by our roundup of Bluetooth speakers for all of our favorite picks.