Re: WOB Corrosion

Thomas Peacock

Hi Kent,

I hope you and Iris are weathering this non-meteorological storm well.

Galvanic corrosion is one of my (many) weak suits, but I’m isolated and have some time to let my imagination go nuts. 

The obvious pattern which appears is that, to my knowledge, you are the only person who has experienced galvanic corrosion of the WOB. You are also the only person who has had his C-drive melted by galvanism. I can’t help but look for a connection. I know that when you replaced the C-drive, you were ultra-fastidious. But, it is a complicated device. I would have to agree with Bill Rouse that I am worried about the C-drive not being protected by the bonding system, and that the WOB is taking the heat for now. I agree that the prop shaft needs to be tested for continuity; I would also test the innermost part of the C-drive that you can access in the engine compartment. My memory is that the C-drive has green and yellow wires attached via the engine frame, maybe also directly to the C-drive. All the wires look good? No chance there are nylon spacers anywhere in the construction?

My memory is that the zinc on the prop shaft is not really necessary, we have a plastic hub. Indeed, the zinc would always fall off in a few months. Someone of authority, not sure if it was Bill or Olivier, explained that the zinc was not necessary. Does it make a difference if you are using steel or nylon bolts to secure it (in terms of your corrosion problem)?

As an aside, I know some owners have foregone the Amel WOB (brass, I think) in favor of a stainless steel WOB. Obviously stainless is more durable to wear, but if you do have a galvanic issue, and if you had a stainless WOB, you might not have noticed anything. I guess the old Captain is right again.

Tom Peacock
SM #240 Aletes
San Juan, Puerto Rico
But I got nervous and flew back to the US

On Mar 29, 2020, at 9:17 AM, karkauai via Groups.Io <karkauai@...> wrote:

Thanks for your replies.
Eric, I am able to turn it on the shaft with rotational  pressure using a screw driver, but I can’t get any purchase on the WOB, as it crumbles when any aftward pressure is applied. I may have to grind it out but will need to get a flexible shaft for my Dremel.  

Danny, I didn’t replace the prop zincs about a month ago when it disappeared, as I knew I was going to haul out and was going on the assumption that I really didn’t need it anyway.

Paul, as Eric said, if you varnish or paint with enamel (fingernail polish works, too) around the holes, they last twice as long.  You said you had plastic bolts holding your prop zinc on.  It should have three hex head stainless steel bolts which would help make contact with the prop.

Gary, the set screws are gone, their holes were so brittle that with  just a little pressure they crumbled.

I will check continuity between the prop shaft and zincs.  If I find no continuity, that would explain the problem.  If there is good continuity, does anyone have an explanation why the rudder zincs are wearing normally but I have this problem with the WOB?

Kent Robertson
S/V Kristy
SM 243

On Mar 28, 2020, at 4:30 PM, eric freedman <kimberlite@...> wrote:

Hi Kent,


That looks like a delicate job. Good luck with the work.


Looking at the picture again, had to tried to put a screwdriver or small chisel in the place where the set screw was and try to rotate the bearing, If you can get it to rotate. Possibly you can get some purchase on the lip of the bearing and pry it out. If I see the photo correctly, a pair of channel lock pliers might allow rotation and removal.


If that doesn’t work and  you have a flex shaft attachment for a dremel tool that would make the work a lot easier. As a jeweler that is the way I would VERY carefully grind out the remains of the bearing.

Another possibility is to drill and tap it in a few places and try  to pull it out with the screws installed in the tapped holes. Use brass screws I case they break off.



If you cover the bolts on the prop shaft zincs with varnish or nail polish, the area around the screws last a lot longer.

Fair Winds


Amel Super Maramu #376



From: [] On Behalf Of karkauai via Groups.Io
Sent: Saturday, March 28, 2020 3:32 PM
Subject: [AmelYachtOwners] WOB Corrosion


Hi All,

I’m hauled out for bottom paint and servicing the Amel-supplied WOB and bow thruster seals.  It has been 4.3 years as I have had Island 44 on the bottom, and it lasts that long.  No water ingress and no oil loss.”, so I haven’t done the service until now.  Please see the pic of the WOB.  It is crumbling apart as if it were damaged by corrosion/electrolysis.  The hull potential has been perfect at -980mv every time I’ve checked it, and the rudder zincs have lasted almost a year with normal erosion.  I have used prop zincs on it since I had the prop shaft electrolysis a few years ago.  They have disappeared after a few months, mostly because they erode at the bolt hole edges and fall off, rather than completely erode away.

It’s going to be a bitch to get out, but bigger question is why did it corrode?  Any thoughts?  

Thanks in advance,
SM 243


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