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Electrolysis and Galvanic Action in Practice and Theory

Oct 19, 2017
6,849
O'Day 19 Littleton, NH
{This thread has lead to a larger treatment of this issue on a new thread based upon Everette Collier's book, 'The Boat Owner's Guide to Corrosion'. If you are interested in joining us, here is the link to the book club page(s):

Section 1: Sailboat Owner's Guide to Corrosion - Basic Theories (Collier 1-4)}
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This subject often comes up as a result of one question or another, someone's prop is pitting, they need to replace their zinc or, in another current thread, are wondering about the wisdom of using a zinc coated brass fitting below the waterline.

I know some general theories of electricity, but have very little practical experience. I am very interested in learning more and I think there are others who feel the same. So, I'm starting this thread to help in understanding the nature and practices around galvanic action and electrolysis aboard.

My understanding of the issue, so that someone who actually knows something can have a place to start and help correct some misunderstandings. This is an issue with direct current, not so much with alternating current, although, it seems like half the time, alternating current could still play a roll.

How I understand electrolysis and electricity to work, is that the less nobel metal has a looser electrical bond to its electrons and thus, in the presence of a high electrical gradient of pressure, will give up those electrons to the more nobel metal. This lose of electrons means a breaking down of the material at an atomic level. In order to do this, there needs to be a conduit or conductive pathway. This is provided by the electrolytic (i.e. saltwater). There also needs to be the electrical pressure. This is a natural gradient between the two metals, but it is made much greater, allowing the movement of electrons to overcome the material resistance between the two metals, when there is a low resistance connection to ground. This makes the connection for a completed circuit. The material that gives up electrons in the anode and the material that greedily sucks them in is the cathode.

I have comme to these ideas from reading about solutions to galvanic action by isolating boats from marina ground and their own electrical systems. It makes sense, however, that a combination of metals that naturally makes a battery, should be capable of creating an independent circuit where the solution they were immersed in allowed the flow of electrons. Another solution I have read about, is to cut off the pathway by coating the metals in teflon or other high resistance insulating materials. Shellac is another insulating material to prevent the loss of electrons. Besides providing sacrificial metals, like zinc, to prevent galvanic material lose, charging a metal with extra electrons should have the same effect. Setting up an electrical anode should take the place of a chemical anode without lose of the anode.

DC Electricity moves at about half the speed of light over a copper wire, but electrons themselves only move a few millimeters per second on average (drift velocity). It is the electron that flows and represents a negative charge. Positive charge is represented by protons, which are much larger and usually fixed in place. Ionized air is filled with electrons and is negatively charged, for example. When the electrical pressure becomes great enough between that ionized air and the positively charged ground, lightning happens.

Ground is a concept representative of a large positive charge. A collection of negative charge (electrons) will be attracted to positive charge. Elections also repel each other, again forcing movement towards the positive charge, but also, significantly, away from each other. This means what multiple pathways can and probably will be taken, as electrons moving along a branch conduit wil choose the path with the least electrons already on the branch ahead.

It seems there are a number of solutions for dealing with galvanic action. More often than not, the only two solutions discussed by sailors are, keeping metals homogeneous and/or adding a sacrificial anode into the mix.

How about it? What's going on with your electrolysis?

-Will (Dragonfly)
 
Oct 19, 2017
6,849
O'Day 19 Littleton, NH
I remember reading about the use of non-sacrificial anodes that work by creating a negative charge to provide electrons to a cathode metal without having to sacrifice a consumable metal. When trying to look it up again, as soon as I include "marine" in the search string, everything references "sacrificial" anodes. Has anyone had experience with electrical anodes to stop galvanic action?

-Will (Dragonfly)
 

DArcy

.
Feb 11, 2017
1,167
Islander Freeport 36 Ottawa
Great thread idea Will. I mostly want to follow this to learn, just a couple of points I can contribute. You mention ground, but a ground reference is not needed to create electrolysis, just an electro-potential difference, one side could be ground but doesn't need to be ground. Sometimes the AC power can have a DC component which is where it can cause electrolysis problems.
Another point to add is, generally speaking, if there is a power source involved it can be considered forced potential difference but there does not need to be an external power source to create electrolysis since any two different types of metal have a different electro-motive potential and can create a current flow if they are electrically connected and there is an electrolyte present - that's how batteries are made. If you have two metals with more than about 1/4 volt separation the anode will give up electrons.
 
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DArcy

.
Feb 11, 2017
1,167
Islander Freeport 36 Ottawa
I remember reading about the use of non-sacrificial anodes that work by creating a negative charge to provide electrons to a cathode metal without having to sacrifice a consumable metal. When trying to look it up again, as soon as I include "marine" in the search string, everything references "sacrificial" anodes. Has anyone had experience with electrical anodes to stop galvanic action?

-Will (Dragonfly)
There are automotive devices which claim to stop rust forming electrically. Search for electronic rust control. Here is one article discussing it
I'm not convinced they work as well as oil sprays
 
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TomY

Alden Forum Moderator
Jun 22, 2004
2,637
Alden 38' Challenger yawl Rockport Harbor
A curious thing to me about electrolysis is, why do most people have no real problems with it? Is it because many of us are floating on moorings, not involved in shore power issues and nearby boats?

I've owned 3 sailboats and can't really recall an electrolysis issue beyond the simple degradation of corrosion which is a far more severe concern in the salt environment.

Books have been written about bonding vs not bonding. I don't see evidence that bonding matters (I've had it both ways), as long as electrical systems are correctly wired.

I have two zincs, conceivably making an electrical connection to the bronze shaft log, but isolated from the shaft- SS, and the prop - bronze, due to cutlass bearing rubber.

One zinc is usually partially eroded, the other minimally(?). The only other zinc is in the HE on the engine. This HE pencil zinc is always entirely eroded away each spring (I don't check mid-season), when I install a fresh one. That HE is ancient, possibly new in the 70's (I swapped it with a re-power).

I have no room for a prop zinc but the prop, at least 45 seasons old, has suffered no electrolysis.

What gives here? Outside of extreme examples of ruined components due to dockside shoddy wiring examples, is electrolysis a boat problem, or more an owner problem?
Prop Speed 6-7-19.jpg
 
Jun 7, 2016
295
Catalina C30 Warwick, RI
The interesting thing is my new to me boat was in the water at a dock every summer for 30 years. It never had a zinc on the prop shaft and up until me replacing it this winter had the original running gear. The original shaft and prop were both bronze and the thru hulls are marelon. So not sure if that was the determining factor.

Now I have a stainless shaft and bronze prop and will be using zincs on the shaft.
 
Feb 14, 2014
5,552
Hunter 430 Waveland, MS
Corrosion is a chemical reaction.

We boaters are most concerned about the

Oxidation of Metals

Oxidation is giving up of electrons.
Guess what?

Metals are full of excess electrons. [ Will called it electrical pressure]
Nature wants to go to the lowest level or stable condition of Oxidation.
____
Example to use is Iron [Fe].
We mine Iron Oxide [dirt] put into a furnace and make elemental Iron. [the opposite of side of reaction or Reduction]

Now we fight chemical reactions to Iron, which nature wants to go back to Iron Oxide.
Redox - Wikipedia

Stopping now on chemistry.
______
Metals on boats always corrode. Designers of boats want to slow corrosion down to an acceptable rate.

So separate corrosion of an Aluminum mast or Stainless rigging, from those metals submerged in water [salt or fresh]

Why?
We can inspect the non submerged stuff easier.

Galvanic Corrosion is mainly in submerged Metals.

End of first Lesson.
Jim...
 
Feb 14, 2014
5,552
Hunter 430 Waveland, MS
Some Metals form a protective barrier of Oxidized metal in Air.
Best example is an Aluminum Mast.
This is a process called..
Anodizing
Making a coating of Oxidized Aluminum

Stainless Steel does too, but designed to use other metals in the Mix to make it more stable and pretty than just Iron.

Titanium and Gold are the best, since they do it very slowly. $$$

This is not true when submerged in Water and in contact with other metals.

So economics play a part on deciding what Metals to submerge.

If we made a Titanium Propeller and Shaft , no worries about Galvanic Corrosion.:biggrin:

Actually true for Stainless if both are the same metal.
Jim...
 
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Oct 19, 2017
6,849
O'Day 19 Littleton, NH
According to wikipedia, these protection systems are called Cathodic Protection Systems
Cathodic protection - Wikipedia
Electrically activated systems are referred to as Impressed Current Systems.

"impressed current cathodic protection (ICCP) systems are used. These consist of anodes connected to a DC power source, often a transformer-rectifier connected to AC power."


They sound more complex than I would have guessed, due to the necessity to measure and vary the charge under changing conditions.


-Will (Dragonfly)
do most people have no real problems with it? Is it because many of us are floating on moorings, not involved in shore power issues and nearby boats?
I had been taught that electrically isolating a boat, such as on a mooring, meant electrolysis wouldn't be a concern, but I'm beginning to think there is more to it than that.

-Will (Dragonfly)
 
Jan 11, 2014
7,628
Sabre 362 113 Fair Haven, NY
Folks, boat don't have a problem with electrolysis.


What boats do have is problems with galvanic corrosion.


Galvanic corrosion can happen because of the underwater metals on a boat by its self or between underwater metals on different boats, a process that can be accelerated by connecting to shore power without galvanic isolation, by diodes or a transformer.

For more on galvanic corrosion and protecting the boat check out Steve D'Antonio's website. Here's a link to an article on bonding:

 
Jan 19, 2010
9,898
Hunter 26 Charleston
Above someone mentioned bonding...if it matters I’m going to postulate that bonding may actually speed up electrolysis...Years ago I read a post about a guy who made a battery charger out of some wire strung in a tree and an old Tesla coil hooked to a spark plug. Hooked to a half dead 12v battery he had it charged up in about a weeks time from static electricity generated as wind blew over the wire. The spark plug was connected to the positive terminal and the negative terminal was connected to a piece of rebar pounded into the ground. I could not find the original post but found this...


so if your standing rigging is bound to your engine and thus to your shaft and prop... and wind strips electrons from your rigging and that pulls electrons from the entire bonded system... corrosion would happen
 
Oct 19, 2017
6,849
O'Day 19 Littleton, NH
made a battery charger out of some wire strung in a tree and an old Tesla coil hooked to a spark plug.
Might it also be possible that he was inducting electrical energy as a dipole antenna connected to a Tesla Coil? With the atmosphere flooded with radio waves, antennas pick up the EMF and convert them into minute electrical charge through induction. Of course, the electrons have to come from somewhere, but it could be that the flow comes from the EMF reception. Tesla coils act as elaborate antennae. However, anything that pushes a charge through your system could accelerate galvanic processes. It would depend, I would think, on whether the charge made your system more positive or negatively charged. If you are collecting electrons from another source, wouldn't that mean the metals with loose electrons to give up, would be less likely to give them up? The cathodic metals would collect their electrons from the freer source.

-Will (Dragonfly)
 

dLj

.
Mar 23, 2017
1,756
Belliure 41 Snug Harbor, Lake Champlain
so if your standing rigging is bound to your engine and thus to your shaft and prop... and wind strips electrons from your rigging and that pulls electrons from the entire bonded system... corrosion would happen
It's my understanding that a properly built bonding system is made only to those components that are submersed in the water. So if someone had bonded their standing rigging to the below water line bonded system, it is incorrectly built and the above is quite true. Using a bonded system is a boat term. I've never heard it elsewhere but maybe it's used somewhere else. In pipelines, when they are using cathodic protection, they bond across high resistance joints, but that is not a system, it's a technique. In boats, as I understand it, bonding, in fundamental principles, is cathodic protection something @Will Gilmore brought up above.

dj
 
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dLj

.
Mar 23, 2017
1,756
Belliure 41 Snug Harbor, Lake Champlain
@Will Gilmore - you have sure raised a large subject. It seems to me if you really want to talk about it here, we would have to start from a much more basic level of defining terminology, what corrosion is, how it works, and a lot more. One of the biggest difficulties I have seen, is that people seem to know some things, get other concepts mixed into it, and generally speaking, there are a lot of misused terms and concepts so to do what you've asked, one would have to start with some fundamental terminology and concepts. This could get very long and complicated..

dj
 
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Jan 11, 2014
7,628
Sabre 362 113 Fair Haven, NY
Above someone mentioned bonding...if it matters I’m going to postulate that bonding may actually speed up electrolysis...Years ago I read a post about a guy who made a battery charger out of some wire strung in a tree and an old Tesla coil hooked to a spark plug. Hooked to a half dead 12v battery he had it charged up in about a weeks time from static electricity generated as wind blew over the wire. The spark plug was connected to the positive terminal and the negative terminal was connected to a piece of rebar pounded into the ground. I could not find the original post but found this...


so if your standing rigging is bound to your engine and thus to your shaft and prop... and wind strips electrons from your rigging and that pulls electrons from the entire bonded system... corrosion would happen
Epistemology, it is the study of how we know what we know. Since the Enlightenment we have refined our knowledge and the manner in which it is gained. The scientific method is one such robust method. It is important to consider the source, is this just one person spouting off, or is there robust and replicable science backing the knowledge?

From the Zetatalk.com website the source of @rgranger's link:

ZetaTalk leads you through the vast amount of information being relayed by the Zetas in answer to questions posed to their emissary, Nancy Lieder.

ZetaTalk answers cover such subjects as portents of a Pole Shift and how this relates to the Transformation in process; how life in the Aftertime following this shift will be different from today; the self-centered or service-minded spiritual Orientation of humans as well as aliens from other worlds and how inadvertently giving the Call to aliens can put you in touch with one group or the other; how Visitations can be more easily interpreted when spiritual orientation is understood; how visitors from other Worldsare watched by the Council of Worlds, which has set Rules regulating their behavior; why we are only gradually getting acquainted with our visitors from other worlds, and what will allow the Awakening to occur faster; to what extent the Government is aware of and interacting with the alien presence; the true nature and reason for the Hybrids being developed by the Zetas to merge the best from both Zetans and Humans; why aliens can disappear and move through walls, and what both physical and spiritual Density changes will be like in the future; what the Zetas have to say about our Science theories; what the Zetas as students of human nature have concluded on what Being Human means; and straight ZetaTalk about our Myths.
Where are Mulder and Scully when we need them? :biggrin:
 
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Jan 11, 2014
7,628
Sabre 362 113 Fair Haven, NY
Even limiting the scope to sail boaters, it can get very complicated.

Perhaps it is too broad to be here. It could be brought into a special subject area - that may be more appropriate.

dj
To understand the relationships between corrosion, galvanic corrosion, stray current corrosion, and related topics, it really requires a structured approach by some who has a good command of the subject and can teach lay persons about the problem. The kind of random, yet well meaning, responses on a forum end up leading the discussion far astray and makes the topic more confusing than it really is. If someone is really interested in understanding marine corrosion, then I'd suggest reading Evertt Collier's book The Boatowner's Guide to Corrosion. It is well written and covers the myriad kinds of corrosion we run into on our boats. @Maine Sail recommended it to me several years ago when I began working on a steel boat that had corrosion issues.

What makes understanding corrosion on boat particularly challenging is the interaction between the electrical systems (AC and DC) and the chemistry of corrosion, compounded by imprecise terminology. This just makes the topic, keeping the metals on our boat in one piece, complicated and confusing.