[PSUBS-MAILIST] Thruster Reliability

[River Dolfi via Personal_Submersibles]

Cliff,
Those sound like signs of an incompatible fluid to me. Especially
considering the length of time that the thrusters were filled with WD40
compared to the hours they have run in the field.

The US Navy created a bunch of technical reports on various aspects of deep
submergence systems design, and distributed them among defense companies
and researchers as part of the "Deep Submergence Systems Project" in the
60's and 70's. All of the documents are now approved for public release and
readily available online. This one is particularly interesting and relevant
to this conversation. I consult it often enough that I have a physical
hard-copy on my office shelf.
"Handbook of Fluid-Filled, Depth/Pressure-Compensating Systems for Deep
Ocean Applications"
https://apps.dtic.mil/sti/citations/AD0894795
There is also:
Handbook of Fluids and Lubricants for Deep Ocean Applications
https://apps.dtic.mil/sti/citations/AD0866350

I suspect that the bushing wear is caused by the low viscosity of the WD40
making it a poor choice for lubrication. I've always been told WD40 is a
penetrating oil, not a lubricating oil.

I maintain and operate a small fleet of ROV's and AUV's that routinely work
at a depth of 6000m. All of them use motors that are compensated with
either univolt transformer oil where high voltages are involved, or a
silicone oil. The caveat being that all of these are brushless electric
motors, so don't have the complications of carbon fouling of the fluid.

We have been evaluating fluids that can serve as both a hydraulic system
oil and an electrical system compensation oil, as we currently run two
separate oils for each function. The problems we are running into are
material compatibility with existing components. Things like wiring, heat
shrink, seals, adhesives, etc. We know what not to do with Silicone and
Univis, but the only way to determine the compatibility of a particular oil
with a particular off the shelf or proprietary component, like a Minn Kota
or any other motor, is testing.

Thanks,

-River J. Dolfi

412-997-2526
rdolfi7 at gmail.com
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