Cetaceans, tubercles, electronics protection, leaks and propylene glycol


These are absolutely 'off the cuff' observations and are offered solely as food for thought. i have more than a passing interest in almost anything biological, particularly biological/tech mimicry.

The first thing that came to mind was the recent innovation with 'props' (mainly helicopter propellers ?) that benefited from improved performance based on the tubercles present on the trailing edges of the fins and tails of certain whale species.

Apparently these small bumps helped to disrupt or enhance the small vertices created by the thrust of the cetacean's swimming movements and added to the efficiency of of their forward propulsion ? Eons of R&D at work.

I recently read that 'DARPA" or like agency had successfully capitalized on this natural design feature by the fairly simple addition of similar small 'bumps' on the trailing edges of helicopter blades ?

This minor modification (if memory serves?) added measurably to the efficiency and stability of the helicopters' propulsion and lift.

I'm wondering if something mimicing that same action might add not only to the efficiency of any ROV propellers but perhaps decrease any water resistance in general with their judicious placement on the surface of the body of the ROV itself ?

Along similar lines, during deep dives cetaceans such as sperm whales. rather than resist the enormous pressures their bodies are subjected to at depth with a rigid outer counter force. Instead 'go with the flow ' as it were, by allowing their highly flexible bodies to actually "collapse" and compress with the pressure, including their large air filled lungs (while at the surface).

This adaptation allows for far greater flexibility and freedom of movement. Though probably not of great importance as such here ? It also helps to dissipate oxygen more evenly and effectively to their core organs. This helps prevent the well known effects of the 'bends' when resurfacing by preventing the reformation of large 'bubbles' as the gasses decompress from solution as the pressure quickly starts to decrease.

What it does do is bring me to the propylene glycol (or similar non toxic, non conductive, non compressible fluid) aspect of my title.

Many of you may have probably witnessed the "science experiment" where someone has taken a TV, computer or other sensitive electronic component and submerged it fully operational into a clear tank of such a liquid without any evidence of ill effects to the electronics ?

I've stretched this simple demonstration enormously with the supposition of "What if" the outer 'shell(s) ' of an ROV's component(s) were encased in some sort of semi-flexible or flexible shell, either single or double walled (mesh encased silicone ?) which was then filled with a similarly propertied liquid ?

Since liquid doesn't compress the addition of an appropriately sized bladder/reservoir to contain the displaced liquid at depth may serve a the same purpose as the cetacean's tissue does with its' displaced gasses when submerged ?

Liquid is more viscous than gas and the flexible outer shell allows the ROV's interior to 'cope' a bit better with the external pressures with a controlled collapse instead of trying to resist the considerable pressures, it also seems less likely to 'leak' for the same reason ?

The non conductive nature of the liquid would also appear to help protect the electronics more effectively from any salt water 'creep' better than an air barrier, and, in the case of shaft/gasket interfaces may also help reduced wear and additional likelihood for leaks with its' intrinsic lubricating action and reduced friction ?

The increased viscosity would not doubt cause some impediment to the motors' rotations so a larger motor and increased attendant power consumption would be needed as an offset and may negate its' use for all but the more extreme conditions ? The current motors being fairly inexpensive and easily replaced.

the liquid is either neutral or slightly buoyant, certainly much less buoyant than the same volume of air, so shouldn't have too adverse an effect in that regard besides a little added weight ?

The liquid's viscosity vs. gas should, in my mind anyway, be lass prone to find tiny areas to cause leaks. Although its' lubricating properties may cause other unseen issues along those same lines ?

admittedly I'm in no way well versed in any of these disciplines so there may be myriad reasons all or little of this missive has any application whatsoever ?

I had just come across your amazing "Kickstarter" project and these among other "outside the box" thoughts immediately found their way from the "box" into my head and then quickly onto your blog for digestion, comment or derision !

Thanks for reading and any thoughts it may provoke. The "box" itself is still pretty full, its' contents' value however, remain open pending critical review.


In the oceanographic field I have dealt with oil filled electronics bottles fairly often. Sometimes it is a small board in some oil filled Tygon tubing. Sometimes it is a rigid box with a bladder (often a finger from a glove) to allow the oil and any stray air to compress. Things to watch out for:

1) Optics usually count on the index of refraction of air. They don't work in oil unless they are designed that way.

2) Hard drives require air. they will crash in oil or vacuum.

3) Electrolytic capacitors, especially large ones, may fail if pressurized.

4) Metal can transistors and ceramic ICs with the soldered on lid may fail at very high pressures.

5) Repairs of oil filled electronics are messy.

6) Power dissipation of many small components is greatly increased.

7) Mineral oil from a drug store usually works well. Peanut oil too.


Interesting things to think about. It sounds like the bumps on the trailing edge of a foil like a propeller help with inducing departure of the boundary layer.

Allowing a body to compress with pressure does reduce a pressure bias, but also changes displacement which can be problematic.

Back-filling the main pressure vessel with mineral oil or some other non-conductive fluid is definitely a possibility if we end up needing to withstand more pressure, but if we get to that point, it will be a happy problem to have.

Thanks for the thoughts!


thank you both for a serious assessment of my "armchair" pondering. after rereading my own posting i can see the shortcoming both of your observations point out.

i also see my 'thought' of a 'displacement bladder' for an already oil filled chamber doesn't make much sense ? nor does the weight of a mile of the thinnest cable on such a small craft at such depths ? (though i hope you do get "there" ! )

my ideas about the oil in general was prompted more by the possible 'protective effects' of oil over air with salt water intrusion under pressure ? the same with the shaft's gasket wearing interface issues.

i guess my primary purpose was an attempt to try and use mother nature's eons of free R&D whenever possible ? i worked primarily with exotic animals so tend to go with things from that perspective.

again thanks for the thoughtful responses.