[PSUBS-MAILIST] Thruster Reliability

Tue Jul 25 19:06:15 EDT 2023

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:
>
>
> <hvwrA_XYbHM4wnAnT6PD23ce1r3TTx98KLljgIsgeatOQqs_ozgPAoDf_LRIrLUnwKqmA7i_6YC
> tq3prbN_uGmkJ1pQsRDVuTtWK9_40l-g=@protonmail.com>
>
> 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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