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Re: WOB Corrosion

karkauai
 

Thanks, Mark.  Interesting to know.  I have a MaxProp Classic.  They sell stainless steel hex bolts for the zinc.
Anyone have suggestions for something I can put between the zinc and aft side of the prop to improve contact?

I was able to remove the bad WOB by drilling two holes and using screws to pull it out.  It came out with just a little coaxing.

See pic.  The galvanic damage extended about half way through the WOB.

I tested continuity between the prop shaft and bonding system and found NO LOAD!!!
Further investigation showed bad connections between the CDrive and engine bed.  After cleaning those up, still NO LOAD. Cable was bad, too, inside the connectors.
I've now confirmed no resistance between the prop shaft and the rudder zincs.

If this had been worse, I could have had catastrophic failure of the WOB, and who knows what kind of other damage...I got lucky this time.

Soooo, bottom line for me is that while hull potential is a good measure of overall bonding efficacy, we must REGULARLY measure continuity at ALL metals exposed to sea water to confirm that they are protected.  It goes on my quarterly maintenance list today.

Kent
SV Kristy
SM 243

On Mar 29, 2020 1:17 PM, Mark & Debbie Mueller <brass.ring@...> wrote:

Hi Kent, 

 

I do like the Dremel idea; it will allow you to section the WOB and remove it like a dentist removes a wisdom tooth. 

 

I wanted to let you know that every time I have ordered prop shaft zincs they have come with the plastic screws.  The zinc has exhibited “normal” wear but has never fallen off.  The Autoprop website has a video showing the rebuild of an H5 and references removing the plastic screws when disassembling the prop.  I believe metal screws provide a preferential contact area on the mounting tabs enhancing the destruction of the tabs whereas the plastic screws spread out the contact area to the body of the zinc – just a SWAG.

 

Good luck with your project.


--
Mark Mueller
Brass Ring  A54

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