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Old 02-23-2011, 08:38 AM   #1
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Help me out here....

Posted below is a pic of my Mainship in the slings. *There is some electrolysis on the strut and on the "shoe" that goes forward of the strut to the hull. *The "shoe" behind the strut and back to the rudder is in perfect condition. *The two "shoe segments" are two seperate pieces of metal as is the strut(obviously). *You can see the bolts that bolt each shoe segment to the strut...that is metal to metal contact as is the contact with the rudder.

My question is, how in the heck can the strut and one side of the shoe suffer from electrolysis while the other segment(and the rudder for that matter) are in perfect shape???? *Especially since they are all connected.


The rudder has a bonding wire to it. *The strut has a bonding wire to it. *The whole bonding system is connected via a galvanic isolator by ProMariner. *The continuity of the bonding circuit has not been checked but that will be completed by the end of the week if not already.


And my ignorance is vast!!!...but my ignorance of electricity is unsurpassed!!! *What am I missing here????


BTW, we hauled to check the structural integrity of the strut. *You can see we added a zinc on the shoe and also we added one to the strut just in case. *The fact that it took us about 20 minutes(with a tag team of drillers) to drill thru one inch of metal with a good cobalt drill bit put my fears to rest...there is still plenty of good metal left. *We just want to stop it. *For now, it is a "watch item". *We will haul again in the fall to take a look.


-- Edited by Baker on Wednesday 23rd of February 2011 09:48:36 AM
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Old 02-23-2011, 08:47 AM   #2
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RE: Help me out here....

Quote:
Baker wrote:

Posted below is a pic of my Mainship in the slings. *There is some electrolysis on the strut and on the "shoe" that goes forward of the strut to the hull. *The "shoe" behind the strut and back to the rudder is in perfect condition. *The two "shoe segments" are two seperate pieces of metal as is the strut(obviously). *You can see the bolts that bolt each shoe segment to the strut...that is metal to metal contact as is the contact with the rudder.


My question is, how in the heck can the strut and one side of the shoe suffer from electrolysis while the other segment(and the rudder for that matter) are in perfect shape???? *Especially since they are all connected.


The rudder has a bonding wire to it. *The strut has a bonding wire to it. *The whole bonding system is connected via a galvanic isolator by ProMariner. *The continuity of the bonding circuit has not been checked but that will be completed by the end of the week if not already.


And my ignorance is vast!!!...but my ignorance of electricity is unsurpassed!!! *What am I missing here????
It would seem to me there is a problem with a connection somewhere

The only other thing it could possibly be is a poor quality of stainless.

Best to*see what the*connections shows when checked out.

SD*
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Old 02-23-2011, 08:52 AM   #3
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RE: Help me out here....

Quote:
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*

The only other thing it could possibly be is a poor quality of stainless.



*

It's bronze....but I still had thought about that....a bad casting of bronze. *BUT, the telltale signs(pink) of electolysis are there! *ANd the shoe was likely made by someone other than the maker of the strut....that is an assumption. *It is, by far, the most elaborate strut I have ever seen and a very "pretty" piece of work....and not cheap as I have already priced the replacement. *We aren't at the replacement point(which is the whole reason for this haul).

*
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Old 02-23-2011, 08:58 AM   #4
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RE: Help me out here....

John,
Post some close up pics. Not that I am smart enough to diagnose it for you, but close up pics would make it much easier to see what you are talking about.
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Old 02-23-2011, 09:01 AM   #5
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RE: Help me out here....

What about stray current.

*The current takes the path of least resistance.

A Galvanic cell has to have been formed somewhere.

Current flowing into or out of the affected area.

Bad connection or bad grounding wire and the boat next to you.

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Old 02-23-2011, 09:07 AM   #6
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Help me out here....

SD, I understand all of that....or maybe I don't. But why would the strut and one side of the shoe be affected by stray current and not the other side of the shoe and the rudder???.....which are all bolted very solidly together!!!....as I type that I remember....not so solidly. We did find some of those strut-to-shoe bolts alarmingly loose. Could that have been the issue??? Maybe a "compound failure"....loose bolts and a bad grounding circuit???

Woodie, my close up pics are on my real camera and I don't have that with me right now. Will get them up tomorrow or Friday.

PS...the ProMariner galvanic isolator panel has a ground monitor on it...it is in the green. *It has a reverse plarity monitor on it....it is in the green. *It has an Isolator monitor on it...it is in the green. *It tests!!!


PSS...galvanic corrsion and electrolysis are two different animals.


-- Edited by Baker on Wednesday 23rd of February 2011 10:11:36 AM
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Old 02-23-2011, 09:41 AM   #7
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RE: Help me out here....

Darned Electric stuff. *You may have a point there with the strut to show bolts, but only as a contributor to something that sounds like a enigma outside of your boat. *I'd take a meter and put the tips into the water at your dock to see what shows. *Please let us know how this proceeds, because there's nothing more valuable than someone finding a solution to an electric problem. *Is there a current in your slip or dock that throws the rudder in one direction or another? *Your rudder standing in the same position for long periods could explain a bit of the uneven electrolysis, especially if the source of the problem is outside.
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Old 02-23-2011, 12:46 PM   #8
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RE: Help me out here....

I always park the boat with the wheel hard over to starboard. So the rudder is always in the same position. BTW, the prop was PERFECT! Not a nick on it...surprised me. I have never seen a prop look so good other than brand new.
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Old 02-23-2011, 12:55 PM   #9
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RE: Help me out here....

Were there any zincs on any of the exposed metal?* Or did it all depend on the remote mounted bonding system zinc bar?

I would think that a zinc directly attached to a bronze or other metal piece to be the best bet.* Maybe they were looking to minimize drag?

Loose hardware could definitely be a problem between the 2 shoes.
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Old 02-23-2011, 01:30 PM   #10
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RE: Help me out here....

It may turn out to be erosion corrosion, caused by prop wash and air bubbles.
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Old 02-23-2011, 01:55 PM   #11
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RE: Help me out here....

As I recently learned, it doesn't take much resistance to block the very tiny amount of electricity that flows through a bonding system. In our case, a brand new transom zinc sitting on its bronze mounting bolts and held on by bolts and washers did not "go away" even though the other transom zinc, mounted in the identical way on the port side of the transom, behaved normally. Not only did the starboard zinc not go away, algae grew on it. which is a sure sign no current is reaching it Yet the mounting bolts for both zincs are hardwired together and there was good continuity between all the mounting bolts, the bonding system, and nearby components like the rudder bars and seacocks.

Needless to say I was very puzzled as nothing had changed on the boat, nothing had become disconnected, and the previous zinc on the same mounting bolts had behaved properly.

At the suggestion of a very knowledgeable marine engineer friend, I removed the starboard zinc (I can do this from the dinghy), cleaned the mouting bolt threads, the nuts and washers with bronze wool and reinstalled the zinc and mounting hardware. I has behaved normally since then. So just because two things like your strut shoe halves appear to be connected together it doesn't take much in the way of a surface film or corrosion or whatever to provide enough resistance to effectively isolate the two components.

If the bronze shoe is scratched down to shiny metal, what color is it? If' it's pinkish, you have a problem. If its bronze colored, maybe not.

But based on our recent experience, if the bonding connections to the strut and the strut shoe are sound and show continuity I would think about taking apart and thoroughly cleaning (with bronze wool or whatever) all the mating surfaces--- bolt threads, washers, nuts, etc. to make sure you've got a good connection the through you shoe and strut components.
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Old 02-24-2011, 12:35 PM   #12
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RE: Help me out here....

Quote:
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It may turn out to be erosion corrosion, caused by prop wash and air bubbles.
Nope...and this is to answer Marin's question too. *It is definitely pink. *ANd Doug, there were no zincs on the affected parts as they were supposed to be protected ny the bonding system. *But we did install zincs for added protection and because it was "easy".

*

My feeble mind says that it would have to be a compound failure somewhere. *If the *bonding wire to the strut is somehow bad, then it's conatct with the rudder(which is bonded as well) should protect it. *But if the connection from the rudder to the shoe to the strut is loose, then maybe that protection didn't take place. *IOW....

*

Loose connection+bonding wire fault= the problem. *take out any one of those two factors and we don't have an issue. *Is this proper thinking?

*

Also, let's assume the boat next to me is putting electricity into the water. *Would my bonding system protect my boat(if everything is working properly) or can electolysis occur regardless of the health of your bonding system?
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Old 02-24-2011, 12:45 PM   #13
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Help me out here....

Quote:
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*1.* Loose connection+bonding wire fault= the problem. *take out any one of those two factors and we don't have an issue. *Is this proper thinking?

2.* Also, let's assume the boat next to me is putting electricity into the water. *Would my bonding system protect my boat(if everything is working properly) ...?
1.* Maybe.* There are a number of possible factors here, from bad connections, to loose wires, to corrosion resistance in a connection, to current leakage in the boat's DC system (and AC system, too, for that matter),**to bad zincs (it happens).* Best thing to my way of thinking is get someone who truly understands this whole bonding thing and electrolysis and galvanic corrosion and have them go over your boat's entire bonding system and components.* In my experience people who meet these qualifications are few and far between so make sure as best you can that*whoever you select knows what they're doing.

2.* No.* From everything I've read and been told by our electrical shop the only thing that will protect your underwater hardware from stray current in the water from another boat is an isolation transformer.* Very expensive.* A galvanic isolator is a different animal altogether and will only protect your boat from stray current in the wrong wires of your shorepower connection.

If a nearby boat is leaking current into the water and it's strong enough it will attack your props and any other metal components (at least bronze ones) in short order*regardless of your bonding system.* I've seen photos of a prop that was destroyed almost overnight*by stray current leaking from a compromised shorepower cable in a neighboring boat.* The current wiped out the boat's zincs very quickly and then went to work on the prop.

-- Edited by Marin on Thursday 24th of February 2011 01:56:34 PM
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Old 02-24-2011, 01:06 PM   #14
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Help me out here....

See Marin, that is what has me totally bamboozled!!!! My rudder is untouched and my prop is in showroom condition...not a nick....it is absolutely perfect!....so much so that I *sat there and stared at it in disbelief!!!

And while I only have a galvanic isolator, it does measure the quality of the ground of the shorepower and it shows it to be okay.

-- Edited by Baker on Thursday 24th of February 2011 02:07:53 PM
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Old 02-24-2011, 01:17 PM   #15
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RE: Help me out here....

Quote:
Baker wrote:

...that is what has me totally bamboozled!!!! My rudder is untouched and my prop is in showroom condition...not a nick....it is absolutely perfect!....
From your description it does not seem like stray current from another boat is the cause of the problem.* I would suspect a bad connection, which as I*described earlier can happen*even if things are*solidly bolted together as our transom zinc was to it's mounting bolts.* Or a bad connection in the boat's bonding wire or strap system.*

As I learned, it takes very little resistance to*"shut off" the flow of current through the bonding system, so a connection that looks as though it should be good may not be if even tiny bit of corrosion or surface "film" has built up between the two things that make the connection.
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Old 02-24-2011, 01:29 PM   #16
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RE: Help me out here....

You said that some of the bolts were loose.

I think that is the problem. They came loose and started to develop corrosion then time compounded the issue. The corrosion blocked the connection to the anode.*I think Marin is right on.**You need to take it all apart and reassemble everything after a through cleaning with an abrasive to get down to good metal. I think you were right with you statement about a compound failure loose bolts and a bad ground. There is really nothing else it could be. Something is causing you strut to be the anode*and not the zinc.
As to where the stray current is coming from is anybody's guess.

The point being is that you are loosing electrons from the strut. If it was properly connected to the sacrificial anode then that would be going. *so it must not be connected.

Just thinking out loud.


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Old 02-24-2011, 01:37 PM   #17
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RE: Help me out here....

Thanks folks!!! I just uploaded the pics...will post here very shortly.
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Old 02-24-2011, 02:00 PM   #18
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RE: Help me out here....

Here ya go....
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Old 02-24-2011, 02:03 PM   #19
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Help me out here....

The zinc on the rudder is about 1.5 months old! Notice the pitting. It was replaced during the survery haulout which brought this issue to light.

Also note that is a 3.5 year old bottom job!!!.....Interlux Ultra Bio!!!


-- Edited by Baker on Thursday 24th of February 2011 03:04:18 PM
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Old 02-24-2011, 02:13 PM   #20
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RE: Help me out here....

Is the ss prop shaft properly bonded to the hull grounding staps?* Just thinkin'
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