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Old 13-03-2023, 08:57   #1
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Grounding Shaft via PSS Shaft Seal: thoughts?

Not sure if this should be in here or the engine subforum, but I'd like to get the community's thoughts on this.

I have a flex coupling/drive saver between the shaft and the transmission so the shaft and prop is no longer electrical connected to ground. I currently have my shaft removed from the boat so that I can replace the bellows on my supplies stuffing box. This shaft seal is the type that has the graphite ring that seals on a stainless shaft collar. Being that graphite is a good electrical conductor, would it make sense to drill and tap a hole in the graphite so that I can connect a ground wire, essentially using the shaft seal as a shaft brush. Transmissions are not generally good at creating a good circuit to the output flange, so I thought this would be better than making a jumper wire to bridge drive saver.

1) I'm not sure how well this would even work, has anyone tried it?

2) As far as I know, I don't have an electrolysis problem, and neither do my dock neighbors. My prop zinc lasts two seasons (April through November). The only zinc that I need to keep after is the one for my raw water cooling and seafrost condenser. Is there a benefit to doing this, or should I just leave well enough alone and not ask for more trouble?
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Old 13-03-2023, 09:09   #2
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Re: Grounding Shaft via PSS Shaft Seal: thoughts?

No, for the same reason PYI ships a plastic barb for the PSS air bleed. The metal will hold heat in the graphite and can cause it to crack.
The proper way to bond around a drive saver is a wire or braid.
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Old 13-03-2023, 09:10   #3
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Re: Grounding Shaft via PSS Shaft Seal: thoughts?

Put a ground wire/flat copper strap on 1 of the bolts holding the coupler together, from the tranny side to the shaft side !
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Old 13-03-2023, 09:38   #4
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Re: Grounding Shaft via PSS Shaft Seal: thoughts?

Quote:
Originally Posted by CaptNemoO2 View Post
Not sure if this should be in here or the engine subforum, but I'd like to get the community's thoughts on this.

I have a flex coupling/drive saver between the shaft and the transmission so the shaft and prop is no longer electrical connected to ground. I currently have my shaft removed from the boat so that I can replace the bellows on my supplies stuffing box. This shaft seal is the type that has the graphite ring that seals on a stainless shaft collar. Being that graphite is a good electrical conductor, would it make sense to drill and tap a hole in the graphite so that I can connect a ground wire, essentially using the shaft seal as a shaft brush. Transmissions are not generally good at creating a good circuit to the output flange, so I thought this would be better than making a jumper wire to bridge drive saver.

1) I'm not sure how well this would even work, has anyone tried it?

2) As far as I know, I don't have an electrolysis problem, and neither do my dock neighbors. My prop zinc lasts two seasons (April through November). The only zinc that I need to keep after is the one for my raw water cooling and seafrost condenser. Is there a benefit to doing this, or should I just leave well enough alone and not ask for more trouble?
If it ain't broke don't fix it.

As others have said the typical way to keep conductivity at a coupler is to run a wire or flat bar from one flange to the other. Another way to do it is to have a commutator brush on the prop shaft. Search "prop shaft grounding devices"
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Old 13-03-2023, 10:05   #5
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Re: Grounding Shaft via PSS Shaft Seal: thoughts?

Could use somehting like this:
www.mgduff.co.uk/products/EE1


I have one fitted aft of the coupling, and the cable connects to the engine block to ensure continuity.
The flexible coupling I have is an R & D coupling which uses a sliver impregnated rubber strip to establish continuity across the coupling.

R and D MARINE : Flexible Shaft Couplings
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Old 13-03-2023, 10:07   #6
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Re: Grounding Shaft via PSS Shaft Seal: thoughts?

Quote:
Originally Posted by CaptNemoO2 View Post
As far as I know, I don't have an electrolysis problem,
Don't go screwing around with the graphite or any part of that assembly.
Is there any particular reason to provide an electrical path to the water via the prop shaft.
Or is it just to do something to see what, if anything, happens, or "fix what ain't broke".
If there is, then as others have said, use a jumper on the coupling.
The "Drivesaver" devices come with a pre-bent piece of flat metal to make that connection should one wish to use it.
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Old 13-03-2023, 11:05   #7
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Re: Grounding Shaft via PSS Shaft Seal: thoughts?

I use shaft brush(es) as part of ssb antenna or lightning mitigation strategy. Some say it can replace shaft zincs. Maybe.
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Old 13-03-2023, 14:52   #8
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Re: Grounding Shaft via PSS Shaft Seal: thoughts?

Quote:
Originally Posted by SY Harmony View Post
No, for the same reason PYI ships a plastic barb for the PSS air bleed. The metal will hold heat in the graphite and can cause it to crack.
The proper way to bond around a drive saver is a wire or braid.
Not saying you're wrong, but I have never seen my shaft seal get more than lukewarm, even after 16 hours of motoring. Also, while my vent line barb is plastic, it looks like the new ones come with stainless steel.
Quote:
Originally Posted by mike d. View Post
Put a ground wire/flat copper strap on 1 of the bolts holding the coupler together, from the tranny side to the shaft side !
When I last put an ohmmeter to measure it, the resistance was very high between the engine and transmission output flange. There's just not a good connection passing through the transmission to be able to use that to bridge the circuit over the drivesaver. I would have to use shaft brushes, which while I have no experience with them, doing some research said they weren't that effective.

The thing I was hoping to fix was to allow the big prop zinc to help augment the little pencil zinc on the heat exchanger so that it lasts a little longer. I guess I'll just keep changing them out. They last most of the season, but if I let it go more than about 6 weeks, the little pencil zinc breaks when removing it from the brass fitting. Then it's a pain to get it out to reuse the fitting. It is not a standard brass NPT plug, it's got a stud for connecting it to the condensor coil since the heat exchanger body is nonmetallic.
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Old 14-03-2023, 04:57   #9
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Re: Grounding Shaft via PSS Shaft Seal: thoughts?

Quote:
Originally Posted by CaptNemoO2 View Post
I would have to use shaft brushes, which while I have no experience with them, doing some research said they weren't that effective.

I've been using a set of shaft brushes for about the last 10 years (replaced the brushes once during that period), and can only say that I have had no issues with them not functioning.
I perodically do a continuity test between the prop shaft and the stud of the hull anode and have always had very good continuity.
When the boat is hauled, I do the check between the prop and the hull anode and again, no issues.
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Old 15-03-2023, 16:41   #10
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Re: Grounding Shaft via PSS Shaft Seal: thoughts?

@CaptNemo #8:
Quote:
The thing I was hoping to fix was to allow the big prop zinc to help augment the little pencil zinc on the heat exchanger so that it lasts a little longer. I guess I'll just keep changing them out.
This scheme will not produce the desire results. The shaft anode and the Hx anodes are in two different bodies of water. One anode has absolutely no effect on the other anode.

Recommend changing from zinc to aluminum on your prop shaft. About 50mVDC more voltage (in cathodic protection, that is a big deal), last longer than zinc, and don't put the heavy metal Cd in the water column where it enters the food chain and ends up in you if you eat seafood. Heavy metal does not treat humanoids kindly.
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Old 16-03-2023, 08:55   #11
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Re: Grounding Shaft via PSS Shaft Seal: thoughts?

What kind of engine/trans do you have?


My Volvo MD2020 specifically says the engine and trans are electrically isolated and do NOT electrically couple them to a common ground.
If your thruhulls are bonded, this is what you would be doing.
Just an FYI
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