Help me out here....

[Baker]

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

 

[skipperdude]

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*

 

[Baker]

skipperdude wrote:

*

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).

*

 

[Woodsong]

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.

 

[skipperdude]

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.

SD

 

[Baker]

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

 

[healhustler]

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.

 

[Baker]

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.

 

[dougd1]

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.

 

[Delfin]

It may turn out to be erosion corrosion, caused by prop wash and air bubbles.

 

[Marin]

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.

 

[Baker]

Delfin wrote:

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?

 

[Marin]

Baker wrote:

*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

 

[Baker]

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

 

[Marin]

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.

 

[skipperdude]

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.


SD

 

[Baker]

Thanks folks!!! I just uploaded the pics...will post here very shortly.

 

[Baker]

Here ya go....

 

[Baker]

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

 

[Avista]

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

 

[skipperdude]

The shaft is isolated from the strut by a bering of some sort. Right?

The shaft zinc is the anode for the prop. Right?

The stainless bolts holding the strut to the skeg are not isolated?

Two dissimilar metals in a salt water solution = a battery.

The stainless bolts become the cathode and the strut (Bronze Less noble) becomes the anode

The stainless bolts are not corroding because they are the cathode.

This would equate to the transfer of electrons from the strut to the sal****er.

The stainless bolts look to be to long as if they are recent additions i.e. not original.

This is how I am understanding the issue .

Tell me if I am wrong.

SD

PS. *Calder says that there are two ways to defeat this problem encapsulate the stainless bolts in bottom paint or some other way or replace them with bronze bolts.



-- Edited by skipperdude on Thursday 24th of February 2011 03:37:14 PM

-- Edited by skipperdude on Thursday 24th of February 2011 03:47:11 PM

 

[Baker]

1)..Yes...the cutlass bearing.
2)I would assume....although the PO had a theory on why not to have a shaft zinc on this particular boat. I listened to him. That shaft zinc is brand new and has not been there during the past 3 years!!!
3)Not sure I understand. But, yes, they are not connected to the bonding system other than touching other metal that is.
4)Understand
5)I thought Bronze would be more noble...although a completely ignorant statement!
6)Maybe.....

So to summarize, you think the stainless bolts are the issue??? Now I know electrolysis causes the pink stuff....does galvanic corrosion cause the pink stuff also??? You are saying I have a galvanic problem when I am thinking it is more of an electrolysis issue??? I am not disagreeing with you. I am just discussing and thinking out loud.

 

[skipperdude]

Galvanic corrosion, often erroneouslycalled electrolysis, is generated by galvanic
action, or the flow of electrical current between
dissimilar metals immersed in an

electrolyte such as seawater.

This is a quote from Nigel Calder the guru on marine corrosion.

As i* Understand it you have a problem with galvanic issues.
the pink is just the indication that the tin in the bronze is migrating thru galvanic action out of the alloy. It makes it week and almost like a sponge i.e .full of holes.

You just can't hav two dissimilar metals in a sal****er solution without forming a galvanic cell and transfering electrons out of the least noble metal to the seaGraphite
Monel
Stainless Steel
Bronze
Brass
Copper
Tin
Mild Steel
Aluminum
Zinc

Thes is the scale of metals most often found on boats.

a fitting made of metal at the bottom of the scale will waste away in seawater
if it is in contact with metal higher on the scale

So to answer to your question it is my belief that you have a galvanic corrosion issue due to dissimilar metals.

SD

 

[Baker]

Hmmmmmmmmm

 

[Baker]

Okay...let's assume it is galvanic corrosion. Why would the aft part of the shoe be unaffected??? And would not the standard bonding system cause the circuit to be connected to a zinc and thus be protected? Again, not disagreeing in anyway. Just thinking out loud. I think you might be on to something for sure.

 

[skipperdude]

You said the rudder zinc is new. It looks to be well pitted.

**Meaning it is doing it's job and sense it is connected to the shoe it is affording some protected by the rudder zinc. the furthe away from the anode (zinc )the less protection.

I am no expert at this but I have done a lot of reading on this stuff.

You said the bolts were loose. the corrosion could have caused the disassociation of the contact thereby negating the effectiveness of the bonding loop.

If you take out one of the stainless bolts is there any evidence of crevas corosion stainless will corrode in the absence of oxygen. white powder in the stainless bolt


SD




-- Edited by skipperdude on Thursday 24th of February 2011 05:13:49 PM

 

[Marin]

skipperdude wrote:
So to answer to your question it is my belief that you have a galvanic corrosion issue due to dissimilar metals.

Yes there is, but that's why there's a bonding system connected to a sacrificial anode.* If the anode is at the bottom of the galvanic chart, or at least significantly lower on the chart than the other metals you have in the electrolyte (the salt water) or that are physically connected together and connected to the bonding circuit, the anode is what goes away first.* Once the anode is gone then the next lowest metal is "attacked."

So if the bonding system is intact, the connections are good, and the anode (zinc in this case) is good, that is what makes connecting dissimilar metals on*a boat possible without deterioration of the metal in the important components.* The "unimportant" zinc deteriorates instead.

Which is the long way of saying that having dissimilar metals in contact with each other either physically or via an electrolyte is fine as long as there is an anode protecting them.

-- Edited by Marin on Thursday 24th of February 2011 06:46:02 PM

 

[Baker]

Mike wrote:

Is that a standard Mainship installation of the prop shaft strut, and rudder skeg?

I can't help you with your underwater metal problem, but I did notice that your propellor shaft nuts are incorrectly installed, which would cause me to question the competency of the yard that works on your boat.

If they didn't know how to install those 2 simple nuts, maybe they didn't know how to install a zinc, i.e clean surfaces, good contacts, and quality parts.

Not all zincs are the same.

Good luck with your problem. I hope it doesn't ruin the upcoming boating season.

Mike
Merritt Island, FL.

That is a stock installation. *It has nothing to do with the yard that works on my boat.....it is not their work. *The prop has never been *removed under my ownership. * *There is plenty of good metal left in the strut...again the reason for this haul. *I just don't want it to get worse. If you read the post, zincs were never an issue or in question here....nor was their installation. *It is the bonding system that is potentially in question.


I do appreciate your input(sincerely). *It just didn't help any other than to point out something MIGHT be wrong and then for whatever reason not share it with me(or the rest of us). *

Sorry, but your post came off as elitist and condescending. *You made some incorrect assumptions and then judgements based on those assumptions. *I probably took it wrong and the context was lost on this here internets.

*

ANd if you are interested in the design of the strut and rudder shoe, it appears that you could cut off the shoe and the lower part of the strut leaving a relatively conventional set up. *It appears to me that Mainship added the shoe for protection of the running gear. *THe strut and rudder are very properly mounted in their own rite regardless of the existence of the shoe...IOW, the shoe and the lower part of the strut are not structural.....again I think Mainship did it for protection.

Edit: *I did do some research reference the prop and I do see what you are talking about if you were referring to the sequence of the nuts. *I also understand why and it is also stated in the ABYC to have the smaller nut forward. *It was interesting that I did come across a few articles stating that it didn't matter. *I guess my question would be...how much does it matter? *In theory it matters I guess. *But it reality, I don't think it would cause any sort of failure in the prop or any sort of damge to it or any surrounding equipment. *But thanks for pointing that out...

IOW, I won't lose sleep over it and correct on the next haul out.





-- Edited by Baker on Friday 25th of February 2011 12:19:29 AM

 

[Baker]

Marin wrote:

*
skipperdude wrote:
So to answer to your question it is my belief that you have a galvanic corrosion issue due to dissimilar metals.

Yes there is, but that's why there's a bonding system connected to a sacrificial anode.* If the anode is at the bottom of the galvanic chart, or at least significantly lower on the chart than the other metals you have in the electrolyte (the salt water) or that are physically connected together and connected to the bonding circuit, the anode is what goes away first.* Once the anode is gone then the next lowest metal is "attacked."

So if the bonding system is intact, the connections are good, and the anode (zinc in this case) is good, that is what makes connecting dissimilar metals on*a boat possible without deterioration of the metal in the important components.* The "unimportant" zinc deteriorates instead.

Which is the long way of saying that having dissimilar metals in contact with each other either physically or via an electrolyte is fine as long as there is an anode protecting them.

-- Edited by Marin on Thursday 24th of February 2011 06:46:02 PM
*



Yep....that is kinda what I was thinking. *Will put a wire in the water tomorrow.

 

[sunchaser]

Baker

Not intending to come across as elitist, but these are simple things to do right with your yard guys on the ground and nearly impossible to do from long distance via the internet. Your yard guys should have the answer, if they don't, oh-oh.*

Yes use several additional zincs, but please ask your yard guys to get a VOM and check the entire bonding wire integrity and also the conductivity for each and every bonding system to metal to hull connection. I believe this has been*touched on*earlier in the thread.