A portion of this video is brought to you
by Surfshark. Hey, want to hear the most annoying sound
in the world? Okay, “most annoying” may be subjective,
but according to a 2017 study from NASA’s Langley branch, humans find the buzz of a
drone’s propellers to be more annoying than any other machine-based sound on earth, which
really limits all the helpful ways we can use drones in big cities. But just by changing the shape of the propeller,
we may have found a way to make drones--and a lot of other things that use propellers--not
just quieter, but way more efficient. Can this propeller really help everything
from quieting tiny drones to helping boats sail further with less fossil fuels? And if just changing the propeller shape makes
such a big impact, why haven’t we tried something like this sooner? I’m Matt Ferrell … welcome to Undecided. Drones: love ‘em or hate ‘em, they are
an increasingly commonplace feature of the modern world. Though they’re probably best known for their
use in photography (or more infamously as weapons platforms), there’s truly an astounding
variety of applications for drone tech, like exploration, forestry, treating weeds on farms,
and safety.[3] You may have seen Mark Rober’s excellent video on Zipline’s drones delivering
lifesaving blood and medicine to distant parts of Rwanda and eventually other cities around
the world. Speaking of deliveries, one often promised
but not-yet-realized opportunity for drones can be found in cargo and shipping services. Amazon has been working for almost a decade
to make drone delivery a real possibility , but concerns about safety, theft and noise
pollution have stymied its development. As I mentioned at the top, humans are very
sensitive to the sound of a drone’s propellers. This is because the buzz they make falls into
the 100 Hz to 5 kHz audible range, which is the same as a crying baby. It could also be compared to the sound made
by flying insects, such as wasps or houseflies, which we’re already accustomed to avoiding. This is a shame because drone-based ‘last
leg deliveries’ emit 84% less greenhouse gasses, and consume up to 94% less energy
per parcel when compared to standard vehicle deliveries. Cargo ships are in the same boat, pardon the
pun. When shipping large amounts of goods, ocean
freight is usually the preferred method because it's so much cheaper to ship items by water
than by air or land. Maritime shipping plays a critical part in
global supply chains, accounting for 80% of global trade by volume. These large ships rely on the dirtiest kind
of fuel - heavy oil fuel - and they can be difficult or expensive to retrofit for clean
energy. As a result the maritime shipping industry
accounts for 3% of global greenhouse gas emissions. Now that might not sound too bad, but if maritime
shipping were its own country, it’d be the sixth largest CO2 producer in the world. Normally drones and cargo ships would be two
very different videos, but one, singular, simple innovation might kill two birds with
one stone. But, other than shipping us stuff, what could
a 3 pound drone and 220,000 ton container ship possibly have in common? Well, they both use propellers. Interestingly, both MIT’s Lincoln Lab and
Sharrow Marine hit upon the same, radically different propeller shape: the toroidal propeller. Instead of the traditional blade design used
by most propellers to generate thrust or lift, these use softly slanting donut shapes, called
toroids. We’ll get into all the benefits this weird
shape provides in a minute, as well as how two different institutions working on very
different projects stumbled upon the same solution. Before we get to that, I’d like to thank
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supporting the channel. So, how did those two institutions stumble
upon the same solution? In both cases, the path to the toroidal prop
was a winding one. Sharrow Marine’s founder, Gregory Sharrow,
was a Berklee College of Music graduate working in video production, when he started tinkering
with propellers to make drones less annoying on film sets. He knew the propellers' tips made most of
the noise, but how could he make a propeller blade with no tip? This initially lead him to the toroidal shape
way back in 2012, and after years of testing and modeling, he thought it would be a better
fit for maritime applications. And here we are … with their prop now on
the market. Conversely, according to Lincoln Labs’ Dr.
Thomas Sebastian, they were working on ionic propulsion for fixed-wing aircraft when they
came across an outdated, turn-of-the-century, ring-shaped wing design. The shape didn’t work well with fixed-wing
craft, but Sebastian wondered if that type of shape could be applied to a propeller,
and thanks to an intern and a 3D-printer, in a few days the team had developed some
working toroidal prototypes. After testing, they found some surprisingly
large improvements in noise pollution and efficiency. What were their findings? How did simply changing the shape fix both
the noise and efficiency issues? As you can clearly see in this test from Sharrow
Marine, a standard propeller creates these small swirls, or vortices at the tips of its
blades, which can create bubbles or cavitations. Surprisingly, the loudest part of a propelled
device isn't the engine or the motor, but the sound made by these vortices and cavitations. Look at this example from Sharrow Marine,
and you can see that not only does the Standard Propeller create noticeable tip vortices,
it also sprays (or displaces) water in a less concentrated manner as the sharrow prop does,
reducing the potential to propel the boat. Here the toroidal and standard propellers
are moving at the same speed. Sharrow’s toroidal propeller is not just
generating far smaller tip vortices, but the dye being pushed out behind it forms a tighter
stream. That equates to more power and efficiency
for the same amount of energy.. This quote from Dr. Sebastian really helps
illustrate what we’re seeing in these tests: “The key thing that we thought was making
the propellers quieter, was the fact that you're now distributing the vortices that
are being generated by the propeller across the whole shape of it, instead of just at
the tip…Which then makes it effectively dissipate faster in the atmosphere. That vortex doesn't propagate as far, so you're
less likely to hear it." In most cases we have to sacrifice some level
of power or efficiency for a quieter ride, but that’s just not the case here. MIT’s best-performing B160 design was not
only quieter at a given thrust level than the best standard propeller they tested, but
it also produced more thrust . The toroidal drone is about twice as quiet as a traditional
drone, and they found that the most annoying sounds - that’s 1-5 kHz range - were the
most reduced. One of the reasons for the sound is the high
speed of the propeller tip. As it passes through the fluid (water or gas),
it lowers the pressure of the fluid. For ships, this means a poorly designed propellor
can lower the pressure enough to actually turn it into vapor- it’s possible to boil
33 F seawater by lowering the pressure. When these gas bubbles burst, called cavitation,
they cause a lot of acoustic noise and can actually damage the propellers. This problem is also found in pumps which
use a rotor to move liquids through pipes in the chemical processing industry. As you saw a second ago in Sharrow’s tests,
these effects are even more pronounced when it comes to hydrodynamics. The toroidal variant sucks in more water than
a traditional propeller, which reduces the amount of water that "slips" out the sides. The result allows the boat to be not just
faster, but smoother and more efficient too. In testing, Sharrow has doubled the speed
a boat can achieve at lower and mid-range RPMs. This broadens the effective rev range of the
motor and reduces fuel consumption by somewhere around 20% (that’s significant when we’re
talking about fuel prices!). Boats also tend to spend the majority of their
time at midrange cruising speeds around 4,000 RPMs. As you can see in this graph, the boat equipped
with toroidal props managed to be 105% more efficient than your average propeller at this
4,000 RPM sweet spot. If just changing the propeller shape made
such a big difference, why are we only hearing about it now? Surely, someone else must have been experimenting
with non-standard propeller shapes? The answer is, of course, yes. The potential energy savings means that almost
every industry with a propeller is toying with its shape. Just like Zipline’s seed-pod-esque propeller
design from Mark Rober’s video. Airbus, a giant in aviation, is testing their
“open rotor” propeller designs, which they claim reduce a passenger plane’s CO2
emissions by 20%. And those are just some of the recent examples. I mean … just look back at the Cold War
stealth submarine race, where both the US and the Soviet Union continually sought to
make their nuclear submarine propellers quieter and quieter. This culminated in the Toshiba-Kongsberg Scandal. Combining Toshiba’s precision machining
tools and software with Kongsberg’s Numerical control device, the Soviets were able to craft
an ultra-stealthy propeller. The US could detect the older, louder subs
from 200 miles out, but submarines with the new propeller were only detectable from 10
miles away or less! So, if practically everyone has been working
on improving propellers for the last 200 years, then why are we only hearing about these developments
now? Sadly, it's just one of those things that
doesn’t usually make it to mainstream headlines. And yet, coincidentally, both Lincoln Lab
and Sharrow Marine recently earned coveted awards in their respective fields. And when a similar design starts making waves
in two different industries, it's hard not to take notice! As exciting as it is, you probably don’t
own a boat, and hopefully you’re not waiting on a drone to deliver you some lifesaving
meds. So, you might be wondering, “Why should
I care?” We’ve already covered the benefits drones
bring if we can make them quieter, but consider the potential of toroids and larger aircraft. Airtravel accounts for 2.5 - 3.5% of global
CO2 emissions, depending on how you tally it. If this tech can be scaled up it presents
another avenue for fuel and energy savings. … and we’ve already touched on just how
much of the global economy relies on massive, diesel-chugging cargo ships. Now, ideally, we’d be able to replace these
with something more environmentally friendly, but in the meantime Sharrow Marine’s toroidal
propellers are already on the market. A radically more efficient ship means a lot
less diesel fumes, heavy metals and carbon being pumped into our seas and skies. If and when these kinds of vessels do make
the leap to greener alternatives, the increased efficiency of toroidal propellers is going
to be a welcome addition. As the pandemic and so-called “port crunch”
inversely showed us, anything that helps these big boats move around the world faster, cheaper
and more efficiently could very well reduce prices on all kinds of goods. As good as that sounds, we just won’t know
if toroidal propeller tech can successfully be scaled-up for big ships and planes until
more tests are performed. And the same unique shape that gives toroidal
props so many benefits comes with manufacturing drawbacks. The novel shape means they’re more complicated
to produce compared to traditional propellers, and this issue only increases with scale. It's not a huge problem for a drone hobbyist
to screw up a toroidal propeller 3D print job, but when we’re talking about a 43 ton
propeller for a cargo ship, any mistake in the manufacturing process is bound to be very
expensive And before we get too far from expenses, as
is often the case with any new technology, these propellers are initially very pricey. Sharrow Marine’s toroidal propeller is going
to run you a minimum of $5,000 for a consumer-sized boat, which is a full ten times more expensive
than a similarly sized, standard-issue propeller. Of course, thanks to the fuel-savings, the
toroidal propeller could pay for itself in time, and a $5K investestment for a minimum
20% fuel savings seems like a no-brainer if we’re just trying to maximize stats. Still, a 1,000% price hike is going to be
a hard sell for a buyer. Then again, as the technology matures and
the manufacturing process becomes more commonplace, that price will likely come down over time. Same goes for 3D printing, which was critical
to the creation of Lincoln Lab’s propeller. 3D printers have vastly sped up the development
process here and elsewhere, and as the tech continues to proliferate we might see tinkerers
create even more radically efficient propellers. At the moment there’s still a lot of testing
to do before we know just which applications are right for this tech, but it’s very cool
seeing such seemingly simple engineering have an outsized impact like this. So what do you think? Jump into the comments and let me know. And be sure to check out my follow up podcast
Still TBD where we'll be discussing some of your feedback. Thanks to all of my patrons, who get ad free
versions of every video. And thanks to all of you for watching. I’ll see you in the next one.
Only 6000$ for my boat, roi at like 35 years… it’s a steal lol