[PSUBS-MAILIST] Thruster Reliability

Tue Jul 25 19:25:57 EDT 2023

 I will send drawings.  I am kind of interested in testing the factor lip seals on the MK 101's.   They look like they can handle a lot more pressure than 30 fsw. 
Cliff
    On Tuesday, July 25, 2023 at 06:07:10 PM CDT, Alec Smyth via Personal_Submersibles <personal_submersibles at psubs.org> wrote:  

 Cliff knows this first hand, but my experience with the WD40 was similar to his. I found the oil went black after just the shortest of use time, and all my thrusters were generating gas. I'd start the day with just a tiny bubble of air in the accordion bottles, but end it with those bottles stretched taut, and a couple of times they blew off or ruptured due to the pressure. I got the impression the electrical arcs on the brushes might be generating gas. 
I'm returning to Michigan next week to pick up the sub, which I left behind to a mechanical breakdown of my tow vehicle. Once I have the sub in hand, I'll take a thruster off and use it to research ceramic seals and the design of a custom endcap. Cliff, I know you use a custom endcap already. If you want to send me the CAD file for it, and I used that as a starting point, it's likely the resulting design would maintain compatibility with your Kort struts. 
One thing that perplexes me is that Hank gets good results with WD-40. I really can't think of anything we're doing differently!
On a positive note, I redid the air compensation for the arm for this trip, and it worked really well. It uses the SS Parker regulator that both Cliff and I used in the past for compensation. My issue with it earlier was that it's OP valve appears to handle only a very low volume, because I was seeing compensation pressure overshoot on ascent. The solution was super simple, I just added a separate OP valve to the compensated line (thanks Alan for the valve suggestion!) This small change makes air compensation attractive again to me, but if we can get 1-atm thrusters to work well, I'd like that even more due to the simplicity. 
Best,Alec

On Tue, Jul 25, 2023 at 6:07 PM Cliff Redus via Personal_Submersibles <personal_submersibles at psubs.org> wrote:

 Good to hear from you my old friend.  I stated out with air compensation using the same pressure regulator that you were using.  I switch out mainly because I was using too much air on deep dives. At that point I only had 80 scf of HP air.  I have since added another 60 scf but still this is not a lot of air for deep dives. Interesting comment about oil impregnating the carbon and then depressurization and getting the "bends".
I think Alec may be on to something with the idea of going back to no pressure compensation and using a single mechanical seal.  Jon just sent me some pictures of the mechanical seal Kittridge had in the K600.    The issue is if there is enough space in the housing to machine out the enclosure. I just don't think there is enough space for the seal without a complete redesign of housing on the Minn Kotas that hold the brushes.
 So I am assuming that the 15 seals on Q-Sub are all air compensated with the same regulators you sent me specs on?  
Cliff

    On Tuesday, July 25, 2023 at 04:11:09 PM CDT, via Personal_Submersibles <personal_submersibles at psubs.org> wrote:  

 I noticed that Karl Stanley promotes air compensation.  I could never
understand why oil ( WD40 etc) was touted as being the preferred medium.  I
would agree with Cliff that the oil has possibly affected the carbon.  I
have had a lot of experience with carbon and mechanical seals and now will
not use it.  The most successful carbon was antimony impregnated in my
experience.  The oils would impregnate the carbon and then with
depressurisation it would get the "bends".  i.e. it would be subjected to
minute explosive decompression which would pit the surface.  The most
successful seals were bronze and silicon or tungsten carbide.  I should
learn from my own mistakes as I have a leaking "carbon"/silicon Carbide
seal. That is only in test mode and has not seen any real pressure.  As I
have so many seals, 15 , I once again got conned into a cheaper solution.  I
think we all collectively have the answers it is just the in depth reviews
of detailed design that is lacking.  Cheers, Hugh

-----Original Message-----
From: Personal_Submersibles <personal_submersibles-bounces at psubs.org> On
Behalf Of via Personal_Submersibles
Sent: Wednesday, July 26, 2023 8:03 AM
To: personal_submersibles at psubs.org
Subject: Personal_Submersibles Digest, Vol 119, Issue 24

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Today's Topics:

  1. Re: Minn Kotta 101 - Thruster Reliability
      (Sean T. Stevenson via Personal_Submersibles)
  2. Re: Minn Kotta 101 - Thruster Reliability
      (Cliff Redus via Personal_Submersibles)

----------------------------------------------------------------------

Message: 1
Date: Tue, 25 Jul 2023 19:22:18 +0000
From: "Sean T. Stevenson via Personal_Submersibles"
    <personal_submersibles at psubs.org>
To: personal_submersibles at psubs.org
Subject: Re: [PSUBS-MAILIST] Minn Kotta 101 - Thruster Reliability
Message-ID:

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Content-Type: text/plain; charset="utf-8"

I have no specific experience with using the WD40 product for pressure
compensating thrusters (or any other volumes, for that matter), but I do
question its efficacy for that purpose on the basis of its known properties.

WD40 is a proprietary mixture of lubricants and solvents known to have
strong dielectric properties. While the exact formulation is a trade secret,
in general terms the product is an emulsion of oil and alcohol. Marketed as
a penetrant, it has a low viscosity afforded by the substantial fraction of
volatile, lightweight components, which help to allow capillary action to
draw the emulsified product into crevices. In unencapsulated service (open
to atmosphere), typically the lightweight components will evaporate into the
surrounding air, temporarily serving their function as a solvent to dissolve
certain solid or high viscosity residues before leaving behind the heavier
oils which serve the lubrication function.

When you encapsulate WD40 in a closed volume, the lightweight components do
not evaporate, leaving them to perform their solvent function on any soluble
material in contact for as long as the equilibrium concentration gradient
supports that. Additionally, you hold these lightweight components with low
viscosity / high volatility (remember, this product is marketed as a
penetrant) in contact with whatever sealing arrangements are designed to
keep it contained, where these seals would otherwise perform much better in
contact with a higher viscosity oil or grease which augments the seal
performance.

In short, for any compensation of electronics in static applications, I
would consider only the dielectric properties and dimensional stability
(bulk modulus) of the compensating fluid. In a dynamic application, such as
with a drive shaft seal, I would also pay attention to viscosity and
lubricity. Material compatibility, however, is critically important in both
cases, and I would be much more comfortable with a product for which the
chemical makeup (and thus the material compatibility matrix) is known and
available on a technical datasheet, versus a proprietary product that has no
such publically available information.

Similarly, with regard to compensating a Minn Kota motor specifically, I
would want to know what all of the internal materials that may be in contact
with the compensation fluid are, to make sure I was specifying a compatible
fluid. I have no idea what information is available in that respect.

Finally, I do wonder how much fluid breakdown is occurring not as a result
of chemical incompatibility, but rather as a result of the brushes lifting
from the armature due to the journal effect of the compensating fluid
forming a boundary layer in between the two parts as they rotate, and a
consequent electric arc forming which jumps the gap and cooks the fluid in
the process. The combination of fluid breakdown and ablation of the brushes
from such arcing could possibly be the source of the blackened fluid, as
opposed to dissolution of the components due to chemical incompatibility.

I find myself wondering if there might be a sweet spot with respect to the
compensating fluid viscosity where the rotor is actually slowed by the fluid
to the extent that the brush contact is actually better than it would be
when rotating faster in a lesser viscosity fluid.

Sean

-------- Original Message --------
On Jul. 25, 2023, 12:11, Cliff Redus via Personal_Submersibles wrote:

> The point of the thread is Psubbers like to use the Minn-Kotta 101 lower
units as a starting point for thrusters because they are cheap, simple to
control, quiet and simple to work on.For my boat I have used these with both
air and oil compensation and have now lost a thruster using each of these
pressure compensation strategies.Typical run lives of trolling motors are on
the order of 5-10 years for boaters. This thruster had less than 20 hours of
run time.How can we boost the reliability of these thrusters?
>
> R300 Thruster Failure, Beaver Island Expedition July 15, 2023
>
> We had a great IS Expedition at Beaver Island on Lake Michigan.Water was
blue, visibility was great, support excellent.Dives were great!That?s the
good news.The bad news is that after a submerged two mile transect when I
surface, I lost the port stern horizonal thruster. Alec?s son Treavor was
the safety diver for the expedition.I asked him to swim over and
inspect.There were no obvious issues like had occurred last year at Lake
Charlevoix when a limb got lodged between the prop and ducted nozzle and
lockrf up rotation.After recovering the boat, I disassembled the
thruster.These are Minn-Kotta 101 lower units that have been modified by
adding hydraulic pressure compensation with WD-40 for the fluid and a small
bellow style bladder for thermal expansion.Before disassembly, I noticed
that the bladder for this unit was completely compressed.The bladders on the
three remaining thrusters were expanded almost to the point of rupture and
were black in appearance.Also, before I di!
 sassembly, I pushed radially on the prop shaft and was rewarded with a
squirt of black 10WD-40.The shaft had a lot more radial play than
normal.From this I could tell the shaft bushing was worn and that both the
thruster lip seals had failed.Upon disassembly, I drained the contents of
the remaining fluid into a plastic pail.See picture at the Psubs web
site.What came out was black WD-40 fluid and a lot of loose black sludge
which was a portion of the brushes.Trolling motors are typically made of a
blend of carbon and graphite also known as carbon-graphite.Upon pulling off
the bow cap and brush end of the trolling motor I found that the surfaces
were caked with black sludge.See picture.Inspecting the brushes showed the
cause of failure.Both brushes were about half the thickness of a new brush
set.One of the brushes springs had bottomed out thus no spring force was
being applied to the brush and thus loss of electrical contact.The WD-40
fluid had been in the thruster since la!
 st year?s Psub convention in Lake Charlevoix.According to the manufacturer
MSDS sheet, WD-40 consist of 30-60% petroleum distillates, 10-30% petroleum
base oils and 5-15% Naptha.My working hypothesis is that one or more of the
components in the WD-40 reacted with the binding agent in the
carbon-graphite brushes and reduced the mechanical strength of the brush
thus leading to accelerate wear.Over the two years period (17,500 hours),
the thrusters had two main dive events with a total of no more than 20 hours
on the units.The balance of the time, the thrusters were sitting on the boat
in my shop soaking in this WD-40 at elevated Texas temperatures.BTW, the
driver for using WD-40 is that is a very low kinematic viscosity (2.8 cSt at
100 F or 38C). Note water is about 1 cSt.
>
> One other observation on the failure was the wear on the armature shaft.It
has a visible wear ring and the shaft bushing went from a snug fit to a
loose fit.Working hypothesis is that the carbon-graphite particles in
suspension were acting like an abrasive polish.
>
> The question is how can we improve the reliability? Should we investigate
a different seal and try to get by with 1-ATM operation or investigate a
different oil or go back to air compensation? What Alec and I discussed at
the Expedition was to try a single mechanical carbon seal or a high
pressure-rated lip seal. If we can come up with something to try, I am
willing to put a Minn-Kotta 101 in my test chamber, power it up so that the
seal in a dynamic mode and increase pressure to failure. A control would be
to run an off-the-shelf MK 101 with no pressure compensation to failure.
>
> Any thoughts?I would like to hear what experience others have had with oil
compensation on MK 101?s.
>
> Cliff
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Message: 2
Date: Tue, 25 Jul 2023 20:02:55 +0000 (UTC)
From: Cliff Redus via Personal_Submersibles
    <personal_submersibles at psubs.org>
To: "Sean T. Stevenson via Personal_Submersibles"
    <personal_submersibles at psubs.org>
Subject: Re: [PSUBS-MAILIST] Minn Kotta 101 - Thruster Reliability
Message-ID: <1367956435.5158416.1690315375216 at mail.yahoo.com>
Content-Type: text/plain; charset="utf-8"

 Minn Kota is very tight lipped about any of the design aspects of their
products.? I guess they are fending off cheap knockoffs.? As such I can find
no real data on materials such as make-up of the brushes.? I am looking at
transformer dielectric oil as a possible replacement
like?https://phillips66lubricants.com/wp-content/uploads/2019/12/Transformer
-Oil.pdf. As to arcing being the possible cause of the blackened fluid, it
is possible, but my guess is a suspension of brush particles given the
amount of sludge left on all the parts and the wear pattern on the shaft.?
What would support arcing hypothesis is that all of these thrusters were
filled using a vacuum pump.? Yet all the bladders experienced gas pressure
build-up.? Likewise, Alec filled all his thrusters with WD-40 and saw
similar blackened WD-40 in bladders and similar gas built up past what you
would expect from thermal expansion of fluid.
Cliff

    On Tuesday, July 25, 2023 at 02:23:16 PM CDT, Sean T. Stevenson via
Personal_Submersibles <personal_submersibles at psubs.org> wrote:  

 I have no specific experience with using the WD40 product for pressure
compensating thrusters (or any other volumes, for that matter), but I do
question its efficacy for that purpose on the basis of its known properties.

WD40 is a proprietary mixture of lubricants and solvents known to have
strong dielectric properties. While the exact formulation is a trade secret,
in general terms the product is an emulsion of oil and alcohol. Marketed as
a penetrant, it has a low viscosity afforded by the substantial fraction of
volatile, lightweight components, which help to allow capillary action to
draw the emulsified product into crevices. In unencapsulated service (open
to atmosphere), typically the lightweight components will evaporate into the
surrounding air, temporarily serving their function as a solvent to dissolve
certain solid or high viscosity residues before leaving behind the heavier
oils which serve the lubrication function.

When you encapsulate WD40 in a closed volume, the lightweight components do
not evaporate, leaving them to perform their solvent function on any soluble
material in contact for as long as the equilibrium concentration gradient
supports that. Additionally, you hold these lightweight components with low
viscosity / high volatility (remember, this product is marketed as a
penetrant) in contact with whatever sealing arrangements are designed to
keep it contained, where these seals would otherwise perform much better in
contact with a higher viscosity oil or grease which augments the seal
performance.

In short, for any compensation of electronics in static applications, I
would consider only the dielectric properties and dimensional stability
(bulk modulus) of the compensating fluid. In a dynamic application, such as
with a drive shaft seal, I would also pay attention to viscosity and
lubricity. Material compatibility, however, is critically important in both
cases, and I would be much more comfortable with a product for which the
chemical makeup (and thus the material compatibility matrix) is known and
available on a technical datasheet, versus a proprietary product that has no
such publically available information.

Similarly, with regard to compensating a Minn Kota motor specifically, I
would want to know what all of the internal materials that may be in contact
with the compensation fluid are, to make sure I was specifying a compatible
fluid. I have no idea what information is available in that respect.

Finally, I do wonder how much fluid breakdown is occurring not as a result
of chemical incompatibility, but rather as a result of the brushes lifting
from the armature due to the journal effect of the compensating fluid
forming a boundary layer in between the two parts as they rotate, and a
consequent electric arc forming which jumps the gap and cooks the fluid in
the process. The combination of fluid breakdown and ablation of the brushes
from such arcing could possibly be the source of the blackened fluid, as
opposed to dissolution of the components due to chemical incompatibility.

I find myself wondering if there might be a sweet spot with respect to the
compensating fluid viscosity where the rotor is actually slowed by the fluid
to the extent that the brush contact is actually better than it would be
when rotating faster in a lesser viscosity fluid.

Sean

-------- Original Message --------
On Jul. 25, 2023, 12:11, Cliff Redus via Personal_Submersibles <
personal_submersibles at psubs.org> wrote:

The point of the thread is Psubbers like to use theMinn-Kotta 101 lower
units as a starting point for thrusters because they arecheap, simple to
control, quiet and simple to work on.? For my boat I have used these with
both airand oil compensation and have now lost a thruster using each of
these pressure compensationstrategies.? Typical run lives of trollingmotors
are on the order of 5-10 years for boaters. ?This thruster had less than 20
hours of runtime.? How can we boost the reliability ofthese thrusters?

R300 Thruster Failure, Beaver Island Expedition July 15,2023

We had a great IS Expedition at Beaver Island on Lake Michigan.? Water was
blue, visibility was great, supportexcellent.? Dives were great!? That?s the
good news.? The bad news is that after a submerged twomile transect when I
surface, I lost the port stern horizonal thruster. Alec?sson Treavor was the
safety diver for the expedition.? I asked him to swim over and inspect.?
There were no obvious issues like had occurredlast year at Lake Charlevoix
when a limb got lodged between the prop and ductednozzle and lockrf up
rotation.? After recoveringthe boat, I disassembled the thruster.? Theseare
Minn-Kotta 101 lower units that have been modified by adding
hydraulicpressure compensation with WD-40 for the fluid and a small bellow
style bladderfor thermal expansion.? Beforedisassembly, I noticed that the
bladder for this unit was completely compressed.? The bladders on the three
remaining thrusterswere expanded almost to the point of rupture and were
black in appearance.? Also, be!
 fore I disassembly, I pushed radiallyon the prop shaft and was rewarded
with a squirt of black 10WD-40.? The shaft had a lot more radial play
thannormal.? From this I could tell the shaftbushing was worn and that both
the thruster lip seals had failed.? Upon disassembly, I drained the contents
ofthe remaining fluid into a plastic pail.?See picture at the Psubs web
site.?What came out was black WD-40 fluid and a lot of loose black sludge
whichwas a portion of the brushes.? Trollingmotors are typically made of a
blend of carbon and graphite also known ascarbon-graphite.? Upon pulling off
thebow cap and brush end of the trolling motor I found that the surfaces
were cakedwith black sludge.? See picture.? Inspecting the brushes showed
the cause of failure.? Both brushes were about half the thickness ofa new
brush set.? One of the brushessprings had bottomed out thus no spring force
was being applied to the brushand thus loss of electrical contact.? TheWD-40
fluid had been in the!
  thruster since last year?s Psub convention in Lake Charlevoix.? According
to the manufacturer MSDS sheet, WD-40consist of 30-60% petroleum
distillates, 10-30% petroleum base oils and 5-15%Naptha.? My working
hypothesis is that oneor more of the components in the WD-40 reacted with
the binding agent in the carbon-graphitebrushes and reduced the mechanical
strength of the brush thus leading to acceleratewear.? Over the two years
period (17,500hours), the thrusters had two main dive events with a total of
no more than 20hours on the units.? The balance of thetime, the thrusters
were sitting on the boat in my shop soaking in this WD-40at elevated Texas
temperatures.?? BTW,the driver for using WD-40 is that is a very low
kinematic viscosity (2.8 cStat 100 F or 38C). Note water is about 1 cSt. 

One other observation on the failure was the wear on the armatureshaft.? It
has a visible wear ring andthe shaft bushing went from a snug fit to a loose
fit.? Working hypothesis is that the carbon-graphiteparticles in suspension
were acting like an abrasive polish.? 

The question is how can we improve the reliability?? Should we investigate a
different seal andtry to get by with 1-ATM operation or investigate a
different oil or go back toair compensation?? What Alec and I discussedat
the Expedition was to try a single mechanical carbon seal or a high
pressure-ratedlip seal.? If we can come up with somethingto try, I am
willing to put a Minn-Kotta 101 in my test chamber, power it up sothat the
seal in a dynamic mode and increase pressure to failure.? A control would be
to run an off-the-shelf MK101 with no pressure compensation to failure.

Any thoughts?? I wouldlike to hear what experience others have had with oil
compensation on MK 101?s.

Cliff

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