The Unexpected Genius of Bionic Propellers

As a former submarine sonar tech you have no idea how terrified of cavitation I am 😂

Recently, I had an enlightening experience while using a small electric motor on my boat. I want to share this because it illustrates the significant impact that underwater noises, like those from propellers, can have on marine life. While I was out on the water, something remarkable happened. I switched the motor into reverse, and to my surprise, a seal popped its head up out of the water. Intrigued, I stopped the motor, and the seal submerged. But when I hit reverse again, the seal resurfaced. This wasn't a one-time occurrence. Each time I alternated between forward and reverse, even from a distance, the seal would respond by appearing while the engine was in reverse. This was particularly striking because the motor I was using was very small and relatively quiet – an electric model. Yet, the seal's reaction was immediate and consistent. This interaction, as amazing as it was to witness, really drove home a crucial point for me. It made me realize the profound effect that underwater noise – from things like propellers and even sonar – can have on aquatic creatures. The fact that even a small, 'silent' motor could elicit such a clear response from the seal underscores the sensitivity of marine life to our human-made sounds in their environment. It's an important consideration for all of us who spend time on the water and a reminder of the broader environmental impact of our activities.

You're telling me his name was Dr. Fish?

I first learned about cavitation and its destructiveness as a mechanic working on Caterpillar hydraulic systems; how it would destroy the vane type hydraulic pumps needed to drive the massive rams on Cat scrapers and loaders. Later I learned about the noise issue as it relates to, particularly, submarines and how the U.S. Navy went to extraordinary lengths to keep the design of its submarine props, enshrouded, LITERALLY, in secret and how they could tell exactly where a Soviet submarine was simply by its noise signature. Even now, when you see pictures of U.S. Navy subs in drydock, their propellers are wrapped to keep them hidden from prying eyes. Truly fascinating stuff.

Marine Biologist Frank Fish? You cannot make this up!

There is a computer fan maker called Noctua from Austria. They have been well known for making quiet fans. If you go their website you will see the same flutes on their fans. This idea came to them more than 20 years ago, after their R&D labs led them to fine tune their observations.

So can these shapes and their effects also be applied to toroidal propellers? Because toroidal propellers seem to already be more effective compared to traditional and traditional with these modifications, so are we able to mix the two ideas in a way where we gain even more effectiveness in the toroidal performance for efficiency and sound reduction?

Probably one of THE MOST important data points I've never even heard about! Absolutely remarkable! I've worked in the U.S.Air Force as a Jet Engine Mechanic and can say I NEVER envisioned this but was completely blown away at the context of this idea - coming from Whale fins??!! How mind blowing!

Just wanted to make a correction. At 1:57 there's a picture of a propeller that supposedly has cavitation damage. This is actually a picture of a brass propeller that's in the process of being repaired. The outer edges have been welded and the "cavitation damage" is actually the weld that was added to repair the propeller. This will be ground down to match the original shape of the propeller. Thought I'd clear that up incase anyone was confused.

I did my dissertation on tubercles, the effect did not seem to be a primary effect of vortex or mixing as would seem intuitive but having a wing with a blend of chord lengths. This in effect smooths the lift/drag distribution so that the wing does not perform as per one specific aerofoil geometry but a blended solution of the chord ranges. This is not so useful for lift generation which can be designed for specified efficient parts of flight but it is useful for maximising the Angles of attack a control surface can be used at - it is not surprising in the end as the humpback whales use the fins for rapid turning and mobility for prey catching, not propulsion.

Cavitation is extremely loud! I was in a ferry. The mechanic took me to see the engine room. He was extremely kind and informative. Then a horrible banging and rumble started very suddenly. It felt like the ship had bottomed out. The mechanic said, "cavitation! We just changed that propeller! I'll be back!" He took off running screaming into a walkie talking about what was going on. I do not know why he was so upset. I did not want to anger the mechanic, so did not ask. He came back a few minutes after things smoothened out and apologised. He was not happy at the operation of the ship. But, I never asked him what issues could arise from the cavitation. This video answered the question.

I must say, having used some 3D CAD/CAM drawing programs to design propellers, these are insanely cerebral from the onset. But introduction of tubercles to the edges makes these ever more insanely complex. Your presentation was professionally presented so that anyone could understand this content without struggling. Good job, Ziroth!

Just as a short side note. The 2 propellers shown use completely different concepts. One is a (water) propeller with structure on the leading edge, the other is a shrouded propeller with structure on the tailing edge. First one is probably good for slow moving air/water the other for fast moving air. Latter is also based on the concept of an owls wing to reduce noise and is already in wide spread use especially in noise reduced ventilation of factory floors (and PCs)

That's why a golf ball with dimples, travels further compared to a similar size ball with no dimples. It seems rough over smooth appears counter-intuitive, but there is definitely some hidden secrets we can learn from nature.

I've long been interested in nature being the template for human design. As a kid I made clay models of cars and ran water over them to see how the natural flow affected the shape. So I'm fascinated to see this.

I don't understand. In your images of whales, the bumps are on the leading edge, and on your model propeller, they are on the trailing edge. Does that make no difference ?

Nature paper says "Our findings present a possible avenue for mitigating cavitation erosion through the application of inexpensive and environmentally friendly materials." It kind of seemed like you were saying GEMS would help mitigate the sound of the propellors and engines, but GEMS allow for louder propellors because the surface coating reduces cavitation damage and not cavitation itself, in theory allowing for faster and louder propellors.

If these were first tested in 2008 with positive results, why hasn’t extra R&D taken place by the major manufacturers of props? The whale being a slow mover has no cavitation to overcome so I find it unlikely it’d be much help with that, an owl on the other hand can fly stealthily with modified feather placement, but with the fluid viscosity being so different, it won’t work in water.

Nice vid. Tho almost every time you say bionic you mean biomimetic.

Applicable to impellers?