Prop shaft electrolysis bonding brush maintenance

[Novaturient Spirit]

Happy Monday all!  >.<

Recently we started hearing a blood-curdling metallic scraping sound with the engine engaged in forward gear. We traced the sound to the electrolysis bonding brush on the prop shaft (pictured). I can't seem to find any info on maintenance of these things... Electrically conductive grease? Or just one of those things you replace?

Does anyone else have this? If so have you ever had to do anything with it?

Thank you!

Best,

Chuck

[Mickey Panayiotakis]

Wow. I've never seen that. Isn't your propshaft bonded to the engine?

I would think some electrically conductive grease would help. I use this ( https://smile.amazon.com/NO-OX-ID-Special-Electrical-Contact-Corrosion/dp/B00HDF9EXE/ ) on all my electrical connections--I got a can from the guys wiring 48VDC when I was building data centers. 

Remember that electrically conductive is not dielectric. I think dielectric is non-conducitve--which might stop the noise but not help the bond any :)

mickey

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[Novaturient Spirit]

Hey Mickey, thanks for the fast reply! I don't know much about bonding, I'm learning on the fly as a result of the scraping sound.  :-)  I don't know if the shaft brush was standard issue on the CR 34 (none of my documents mention it) or if a previous owner added it on. The prop shaft does bolt on to the transmission, though I've read a couple accounts that that doesn't necessarily mean bonding to the engine -- allegedly the lubricating oil in the gear box offers sufficient resistance to make direct bonding of the shaft desirable?? I have lots more reading to do.

This looks like what I'm looking at: https://www.amazon.com/dp/B00DH3UBVA/ Rather amusing it's in the Hair Care / Hair Brushes category. =^D

Thanks so much for the super-helpful lead on the conductive grease!

Chuck

[Thierry Danz]

Chuck,

Are you sure it is coming from the carbon bonding brush? I don't have one of those on my CR42 but had one on another boat. It is a piece of carbon that should be slippery enough by itself that it doesn't need grease. They will run out, eventually. When you pull it away from the shaft does it still look that it has enough carbon left?

Thierry

[Novaturient Spirit]

Hi Thierry! Thank you for these ideas. I'm not familiar with this brush so it's hard to say. It's not all the way down to the metal strip that supplies the springy pressure -- there is still a small block of something protruding off the end -- so I imagine it's the original carbon material on there, though I can't say it feels slippery to the touch. I wiped it off in case of foreign particles, but after that it still makes a scraping sound. (If the brush is held off the shaft by hand, no scraping sound; if the brush is allowed to contact the shaft, scraping sound.) There's no evidence of scoring or other damage to the shaft. I'll take another look at where the carbon is, but honestly I'm not sure what I'm looking for.

Chuck

[Mickey Panayiotakis]

Great info as always, Thierry.  I didn't realize there was a carbon bit on there.

Any ideas what types of transmissions might require this instead of bonding through the transmission?

On Mon, Dec 5, 2016, 21:15 Novaturient Spirit <novaturie...@gmail.com> wrote:

Hi Thierry! Thank you for these ideas. I'm not familiar with this brush so it's hard to say. It's not all the way down to the metal strip that supplies the springy pressure -- there is still a small block of something protruding off the end -- so I imagine it's the original carbon material on there, though I can't say it feels slippery to the touch. I wiped it off in case of foreign particles, but after that it still makes a scraping sound. (If the brush is held off the shaft by hand, no scraping sound; if the brush is allowed to contact the shaft, scraping sound.) There's no evidence of scoring or other damage to the shaft. I'll take another look at where the carbon is, but honestly I'm not sure what I'm looking for.

Chuck

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[Thierry Danz]

Mickey,

I am certainly not an expert on bonding. I don't think the transmission is the issue. But if the coupling between the shaft and the engine transmission is isolated, e.g. by a non-metallic flexible shaft coupling, you need to electrically connect the shaft to the bonding system. You can do that with a jumper across the coupling, or by a carbon brush.

Thierry

On Mon, Dec 5, 2016 at 9:25 PM, Mickey Panayiotakis <svb...@gmail.com> wrote:

Great info as always, Thierry.  I didn't realize there was a carbon bit on there.

Any ideas what types of transmissions might require this instead of bonding through the transmission?

On Mon, Dec 5, 2016, 21:15 Novaturient Spirit <novaturie...@gmail.com> wrote:

Hi Thierry! Thank you for these ideas. I'm not familiar with this brush so it's hard to say. It's not all the way down to the metal strip that supplies the springy pressure -- there is still a small block of something protruding off the end -- so I imagine it's the original carbon material on there, though I can't say it feels slippery to the touch. I wiped it off in case of foreign particles, but after that it still makes a scraping sound. (If the brush is held off the shaft by hand, no scraping sound; if the brush is allowed to contact the shaft, scraping sound.) There's no evidence of scoring or other damage to the shaft. I'll take another look at where the carbon is, but honestly I'm not sure what I'm looking for.

Chuck

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[Mickey Panayiotakis]

Hey Thierry

I'm aware of the issues with installing a flexible coupling (I have one, but for other reasons) and the need to bond if you do. However Chuck mentioned something different I haven't heard of before:

> The prop shaft does bolt on to the transmission, though I've read a couple accounts that that doesn't necessarily mean bonding to the engine -- allegedly the lubricating oil in the gear box offers sufficient resistance to make direct bonding of the shaft desirable?? 

Any ideas?

mickey

[Thierry Danz]

I've read that too somewhere. On Curlew I just rely on the prop and shaft zincs.

Thierry

[Novaturient Spirit]

Installed a new brush over the weekend. No more scraping! Here's a side-by-side look at the old and new.

Chuck