Galvanic Corrosion

[techspecial]

This could really start an interesting series of responses...
I'm an electronics guy but I see so many differing opinions about the causes of galvanic corrosion. We all know about keeping your zincs in top shape and making good electrical contact with whatever they're connected to. Getting a little deeper we can refer to the table of noble metals and see that some metals are more sacrificial than others and will eventually suffer more in salt or brackish water. All boats that are connected to shore power should be grounded properly and the use of an isolator is the ideal situation. But my question is: During tide changes on floating docks shore power cables sometimes accidently end up in the water. Will a cable that has no damage i.e. nicks, cuts, cracks etc. contribute to galvanic corrosion? Some people in my marina have heated arguments with their neighbors about this and I think that it's all BS. I know that if you have a next door neighbor that isn't following the rules other that the cable in the water, you're in trouble. I just don't think that the cable in the water has any effect...THANKS IN ADVANCE!!! Mike the nuke...

[MOP]

Quite a few years back Sven Johnson of Johnson Labs was hired by Perelli to the electric cable spanning from Point Judith RI to Block Island. The island was battling the main land over the high electric usage that they said they were not using. When the cable was checked it showed of high readings, the cable lays mostly exposed in the deeper water buried near shore. I got to photos of the massive layers of insulation in a cross section of the cable it was hard to believe it could possibly leak. So I would say yes!

Phil

[cutwater]

If there is an adequate insulator on the cable, should be no problem. Water is a poor conductor, but still much better than the wire insulation. So even if there was 110V or 220V from line level to the hull, most of the field will be developed across the insulation. If proper materials are used, I don't see how you could expect any adverse effects.

[BillG]

I can tell you this from first hand experience. I was docked next to a boat that had a battery charger hooked up to it for a length of time and after just a week my aluminum prop was a swiss cheese. My boat had been in salt water for many years before this and never had any problems.

Bill

[DonziJon]

I can tell you this from first hand experience. I was docked next to a boat that had a battery charger hooked up to it for a length of time and after just a week my aluminum prop was a swiss cheese. My boat had been in salt water for many years before this and never had any problems.
Bill

I had this exact problem with my 32' sailboat at a marina in salt water. Lost a 15" BRONZE prop in one season. The guy next to me had a "do it yourself" battery charger installation on his boat. I showed him my prop at the end of the season and he just shrugged. Ignorance is bliss. :bonk: John

[txtaz]

This could really start an interesting series of responses...
I'm an electronics guy but I see so many differing opinions about the causes of galvanic corrosion. We all know about keeping your zincs in top shape and making good electrical contact with whatever they're connected to. Getting a little deeper we can refer to the table of noble metals and see that some metals are more sacrificial than others and will eventually suffer more in salt or brackish water. All boats that are connected to shore power should be grounded properly and the use of an isolator is the ideal situation. But my question is: During tide changes on floating docks shore power cables sometimes accidently end up in the water. Will a cable that has no damage i.e. nicks, cuts, cracks etc. contribute to galvanic corrosion? Some people in my marina have heated arguments with their neighbors about this and I think that it's all BS. I know that if you have a next door neighbor that isn't following the rules other that the cable in the water, you're in trouble. I just don't think that the cable in the water has any effect...THANKS IN ADVANCE!!! Mike the nuke...

Galvanic corrosion is caused by a difference in potential between two metals. Electrons pass from the higher potential metal to the lower metal causing erosion due to dissimilar metals. The difference is in the metals outer electron layer. This difference is measured in Volts. If anyone remembers bi-medal temperature measuring, this is the principal it works on.

So to answer your question: Yes!

Ok, I'll explain LOL...Shore power cables are at a higher potential than anything on your boat. Hence extra electrons which aids the transfer of electrons in dissimilar metals. So cracked insulation or freely dangling cables (especially in salt water ) will cause problems. The zink is used because it absorbs free electrons. Hence sacrificial. When extra electrons are absorbed, zinc turns to zinc oxide which is water soluble and looks like flakes much like lead oxide in your battery.

Questions? Anyone??? Bueler??? Bueler???
Da Taz<---Science class is ajurned

[zelatore]

Galvanic corrosion is caused by a difference in potential between two metals. Electrons pass from the higher potential metal to the lower metal causing erosion due to dissimilar metals. The difference is in the metals outer electron layer. This difference is measured in Volts. If anyone remembers bi-medal temperature measuring, this is the principal it works on.
So to answer your question: Yes!
Ok, I'll explain LOL...Shore power cables are at a higher potential than anything on your boat. Hence extra electrons which aids the transfer of electrons in dissimilar metals. So cracked insulation or freely dangling cables (especially in salt water ) will cause problems. The zink is used because it absorbs free electrons. Hence sacrificial. When extra electrons are absorbed, zinc turns to zinc oxide which is water soluble and looks like flakes much like lead oxide in your battery.
Questions? Anyone??? Bueler??? Bueler???
Da Taz<---Science class is ajurned

Bzzt!
The first part about the difference in the potential of different metals is right.

The 'yes' answer, however, is not.

The short (ha-that's a joke, son!) of it is that if the power cord is in good shape and the insulation is in-tact, the only thing that happens if part of it droops into the water is it gets a lot of growth on it and you have to clean the mess up.

(I’m assuming the hot end of the cable is not hanging in the water, only that a cable plugged into the dock and boat correctly is partially submerged in the middle)

There is no path for the electricity to flow to the water unless there is a breach of the insulation.

The only possible issue would be induction due to the AC power, but this is not at fault with your corrosion issues.

Electricity in general is not well understood by most people. After all, you can't see it so it's only grasped on a theoretical level. Small boat owners also generally don't deal with shore power systems; again, most small boats don't even have a shore power system. Most 'experts' on the dock just lump any underwater corrosion into the term 'electrolysis'. Actually, it's far more complicated that that. And while a dock or boat's poor wiring may (will) indeed affect other boats in the marina, a good condition shore power cord hanging in the water will not.

It will make a mess; it might pose a safety issue (if it were to drop the hot end into the water); but it's not causing any sort of corrosion on it's own.

Here are a few links if you want to study up. It's a much misunderstood topic, and you can even find some conflict between the articles.

http://www.practical-sailor.com/newspics/charts/883marinecorrosion.pdf

http://www.yachtsurvey.com/corrosion_in_marinas.htm

http://www.boatus.com/boattech/MarineCorrosion.htm

[cutwater]

Electrons pass from the higher potential metal to the lower metal

Have to disagree... :wink:


Ok, I'll explain LOL...Shore power cables are at a higher potential than anything on your boat. Hence extra electrons which aids the transfer of electrons in dissimilar metals. So cracked insulation or freely dangling cables (especially in salt water ) will cause problems. The zink is used because it absorbs free electrons. Hence sacrificial. When extra electrons are absorbed, zinc turns to zinc oxide which is water soluble and looks like flakes much like lead oxide in your battery.

Everyone seems to be talking about cracked cables or homemade battery chargers... But the question only applied to properly insulated cables, in which case there is no current flow as the larger field is developed across the insulation, not the water.

[cutwater]

Nice post Don.

[joseph m. hahnl]

Have to disagree... :wink:



Everyone seems to be talking about cracked cables or homemade battery chargers... But the question only applied to properly insulated cables, in which case there is no current flow as the larger field is developed across the insulation, not the water.

I would think that there is no such thing as a fully insulated cable. It would only take a micron hole to bleed current. Just because you don't get shocked doesn't mean there isn't any current escaping. I also believe that all wires with current create an electric field. You may not detect as it is not high enough to shock a person. "Not sure" but I think they give off Rf signals too.

Now that in it self may not be enough to destroy your neighbors prop.
I think for the sake of keeping the peace don't let be a continual thing

[yeller]

I also believe that all wires with current create an electric field.

Not an electric field, but an electromagnetic field. All AC current produces a magnet field. DC current does not.

[zelatore]

Not an electric field, but an electromagnetic field. All AC current produces a magnet field. DC current does not.

Exactly. That's how your basic inductive 'clamp' style AC meter works.

But as mentioned before, this is not a cause of underwater corrosion on a boat.

[txtaz]

Oooopppssss, I re-read the original post.

The question is about cables in good condition. My bad. So the answer would be no. However there could be dielectric leakage which would be extremely small.

Cutwater, electrons do pass between dissimilar metals and can be measured. The most common use are called bi-metals and are used for temperature measurement. However the principle of electron transfer is the same no matter what the material. It doesn't matter if you believe the electron theory or the hole theory, electrons are moving between materials of differing potentials. (potential is measured as the difference in electrons) It is because most all material have ions or are ions. Which is an excess or deficiency of electrons in the valance shell (2n^2 rule). So the transfer of electrons through one material or dissimilar materials is called current. The number of electrons to pass through one point in one second with one volt potential is one amp. This is the standard and I think it was set using copper as the material.

zelatore, dc current does produce an electromagnetic field (think of the starter in you car). However it is a constant field if current is constant. ac current is always changing which is why the field is always changing.

Hope this clears things up.

Da Taz<---I learned by watching Mr. Wizard.

[cutwater]

No, I "believe" the theory, haha :wink:. I'd get fired if I didn't. Although you can't just believe in one of them, they are both essential to understanding charge transfer.


Electrons pass from the higher potential metal to the lower metal

I only disagreed with this statement, as I noted... My point was electrons pass from the lower potential to the higher potential. Positive current passes from high-->low, but in reality describes the opposite direction of electron flow.

[txtaz]

My point was electrons pass from the lower potential to the higher potential. Positive current passes from high-->low, but in reality describes the opposite direction of electron flow.

OMG, I ran across a hole theorist. This is a first for me. General physics believes the electron principal. Negatively charged electrons move to valance shells bouncing out another electron and so on.

Also, current direction is a point of relativity. Which way are we looking at it? Right to left? Left to right? And the big question...Does it matter? And no it has no relevance to Einstein's equation. We can debate that if you choose. LOL Hymmm, a new thread???

Da Taz<---Albert who???

[zelatore]

zelatore, dc current does produce an electromagnetic field (think of the starter in you car). However it is a constant field if current is constant. ac current is always changing which is why the field is always changing.

OK, I believe you're right. But if I remember correclty, it's the collapse of that field that causes a transfer via induction into a nearby conductor. Thus explaining how transformers work or my laymen's example of an inductive clamp-type meter.

(I'm ashamed to admit my degrees are in electronics but I haven't actually used that training in over a decade so I'm a tad rusty)

[cutwater]

OMG, I ran across a hole theorist. This is a first for me. General physics believes the electron principal. Negatively charged electrons move to valance shells bouncing out another electron and so on.

You're losing me here... Look at any, and I mean ANY, electronics textbook... Holes are a universally accepted way of describing the absence of an electron... Please, go check out every single device physics book you can find, and talk to every IC designer you know...


Also, current direction is a point of relativity. Which way are we looking at it? Right to left? Left to right?

Yes, but electrons always tend toward the higher potential in order to achieve equilibrium, regardless of how you decide to define current.

[txtaz]

OK, I believe you're right. But if I remember correclty, it's the collapse of that field that causes a transfer via induction into a nearby conductor. Thus explaining how transformers work or my laymen's example of an inductive clamp-type meter.
(I'm ashamed to admit my degrees are in electronics but I haven't actually used that training in over a decade so I'm a tad rusty)

You are so close...It's the expanding or collapsing of the electromagnetic field that induces potential in a near by conductor. This is the principle that transformers, amp meters and inductors work on. Remember there are 5 time constants for the field to build or collapse and is why construction of coils is tight tolerance. They use varnish for insulation. Now that's tight.

Da Taz

[zelatore]

Negatively charged electrons move to valance shells bouncing out another electron and so on.

That's what I was taught, but I'm not a physicist. Heck, I don't even play one on TV.

[txtaz]

That's what I was taught, but I'm not a physicist. Heck, I don't even play one on TV.

Yeah, well I stayed at a Holiday Inn Express last night.:eek::eek:

Da Taz

[zelatore]

You are so close...It's the expanding or collapsing of the electromagnetic field that induces potential in a near by conductor. This is the principle that transformers, amp meters and inductors work on. Remember there are 5 time constants for the field to build or collapse and is why construction of coils is tight tolerance. They use varnish for insulation. Now that's tight.
Da Taz

You are beginning to sound suspiciously like an engineer. Or worse yet, a physicist. As a lowly technician, I don't think I can trust you. :wink:

Standard engineer vs technician joke:

An engineer and a technician are in a bar and spot a hot girl. She makes eye contact with them both and they say to each other 'hey, she likes me...I could get lucky!' But each time they move toward here they only cover 1/2 the distance. Since theory says that if you only move 1/2 way with each step you'll never arrive at your destination, the engineer gives up saying he’ll never reach her and it’s pointless to try. The technician keeps going on the premise that he'll get close enough that in the real world it won't matter and thus gets the girl.

Of course, the real punch line here is the idea that a hot girl would be interested in either a tech or engineer.

[yeller]

zelatore, dc current does produce an electromagnetic field (think of the starter in you car). However it is a constant field if current is constant. ac current is always changing which is why the field is always changing.

Don't blame zelatore, I was the one that brought it up. Yes taz you are right. I wasn't thinking straight. DC will create a constant magnetic field, where as AC will create one, then it will collapse, and repeat. I was thinking more of inducing a current. DC won't where AC can ie: transformers, etc.

EDIT: Now finished reading the rest of the thread and looks as I'm a little slow in answering.

zelatore, good joke. I always use the 1/2 way thing to explain why I'm not where I should be.

[techspecial]

Gosh, I didn't think I'd ever hear an argument about electron/hole theory since I graduated in the seventies!!! Countless beers and shots ago..
I'm just a lowly technician because we make more money than engineers at my nuke...But we still loose the girls to those cool Annapolis submarine guys!!!
Should I tell the guys who complain about their neighbors cords in the water to shut up or are they right? I'm the Commodore at my club so I need something to say at our next meeting...The Commodore thing still doesn't work with the girls though...Maybe if I move up to a 22C with a big block that'll work!!!:confused:

[txtaz]

I'm just a lowly technician because we make more money than engineers at my nuke...But we still loose the girls to those cool Annapolis submarine guys!!!


Nuclear engineer Mon...No way to go. Been there done that and on subs. We would get all the girls if we had free time. Or at least maybe we would. Nothing worse than hitting Hawaii for 5 days and not being able to shut down the reactor or go see anything. Not to mention all the other cool places I can say I've been and haven't seen.

I would approach your problem as a housekeeping sort of thing. Remind people that proper attention to lines, cords, grounding etc is always a good thing and does not take much time. Also, it makes good neighbors and saves money. Don't take a stand...It will offend someone. Foster an environment that each other wants to help others. Hymmm, much like here.

AND yes, get the 22c with a BB. If you don't get the girls, you will still end up with a smile on your face at the end of the day.:wink:

Da Taz<----Dive, dive, dive...OneSubDriver make depth 60 feet. All hands to general quarters.

[DonziJon]

Nuclear engineer Mon...No way to go. Been there done that and on subs. We would get all the girls if we had free time. Or at least maybe we would. Nothing worse than hitting Hawaii for 5 days and not being able to shut down the reactor or go see anything. Not to mention all the other cool places I can say I've been and haven't seen.
I would approach your problem as a housekeeping sort of thing. Remind people that proper attention to lines, cords, grounding etc is always a good thing and does not take much time. Also, it makes good neighbors and saves money. Don't take a stand...It will offend someone. Foster an environment that each other wants to help others. Hymmm, much like here.
AND yes, get the 22c with a BB. If you don't get the girls, you will still end up with a smile on your face at the end of the day.:wink:
Da Taz<----Dive, dive, dive...OneSubDriver make depth 60 feet. All hands to general quarters.

WOW: Another Bubblehead. :smash: I used to do "Scopes" when I was in the Navy back in the sixties. Subase, NLon.

BTW: I love it when you guys talk dirty....what with all that tecky stuff and whatnot. :cool: John

[dwiggl]

There was a great article in "Professional Boatbuilder" about a year ago on leaky circuits. Some real horror stories of the damage that occurred from tiny insulation failures poor understanding of circuits & grounds. The worst stories were about kids swimming off dad's boat at the marina; not rapid corrosion.
In fresh water the human body is a better conductor than the H2O as we are "salty". So the path of least resistance is through our heart. If an adult jumps in next to the do-it-hisself wiring guy we may feel a tingle and be able to swim out of range of the elect field. If a kid jumps into the same area their little heart stops.
If I remember the article correctly, the court decided it's manslaughter. Regarless of where you sit on the decision, it's dangerous stuff.
So what I want to know is, whenever I swim off the back of the boat with my bride of 22 years, the electricity starts flying. Does that mean my prop is gonna corrode?
dw

[txtaz]

In fresh water the human body is a better conductor than the H2O as we are "salty". So the path of least resistance is through our heart.


Ahh, that depends on frequency. The higher frequency current tends to travel closer to the surface of shin which is why 120V/60 hz is the most dangerous.


Does that mean my prop is gonna corrode?
dw

Only if you cheated on her and she found out. And that would be the prop corroding against the side of you head.:hangum:

Da Taz<---Faithfull because I can't afford extra props.

[onesubdrvr]

Nuclear engineer Mon...No way to go. Been there done that and on subs. We would get all the girls if we had free time. Or at least maybe we would. Nothing worse than hitting Hawaii for 5 days and not being able to shut down the reactor or go see anything. Not to mention all the other cool places I can say I've been and haven't seen.

I would approach your problem as a housekeeping sort of thing. Remind people that proper attention to lines, cords, grounding etc is always a good thing and does not take much time. Also, it makes good neighbors and saves money. Don't take a stand...It will offend someone. Foster an environment that each other wants to help others. Hymmm, much like here.

AND yes, get the 22c with a BB. If you don't get the girls, you will still end up with a smile on your face at the end of the day.:wink:

Da Taz<----Dive, dive, dive...OneSubDriver make depth 60 feet. All hands to general quarters.
1) Time, yes.... very little when locked up in a sewer pipe for 90 days at a time,... hell, come to think of it, no chicks,...... no fresh air,...... no sun,..... oh and sports scores ONLY if you did good enough on your drills

2) Good housekeeping, not only is it a houshold term, but a submarine one too,.... heck, don't forget the sound silencing surveys, and field days,... maybe that's what is needed at your marina, a good field day, if that line doesn't belong there, get rid of it ;)

3) Make depth six-zero feet aye,.... hey, did you close the haaaaatc blurb blurb bubble

[txtaz]

QUOTE=onesubdrvr;463546]1) Make depth six-zero feet aye,.... hey, did you close the haaaaatc blurb blurb bubble[/QUOTE]

Now that's funny. Who's job was it to close the door anyway?

Da Taz<---Only did a few tours on the con for quals. At least I didn't run into anything.

[onesubdrvr]

QUOTE=onesubdrvr;463546]1) Make depth six-zero feet aye,.... hey, did you close the haaaaatc blurb blurb bubble

Now that's funny. Who's job was it to close the door anyway?

Da Taz<---Only did a few tours on the con for quals. At least I didn't run into anything.[/quote]

Anything that the Navy will release anyway ;)

There was the one boat that left CT. in 1996, and didn't lower the scope before going under the bridge,.... that was a short deployment. :doh:

As far as I know, it was Carl's job to shut the hatch

I spent alot of time as DOOW, COW, and in my early days, Helms/planes. Most of my time was spent in the room with the bomb :shocking:

Wayne :)

[Ghost]

This has been a fun read--been a while since I pondered this stuff.

(As a quick aside, I concur that the flow of electron holes is the standard way of describing positive current. :))

TWO SCHOOLS OF THOUGHT THAT BOTH SEEM RIGHT:
On the one hand, I find extremely compelling the empirical stories of guys here whose props turned to swiss cheese next to shorepower-rigged boats, especially since they had years of happy experience prior to the shorepower guys showing up.

And at the same time, the discussion of cables with good insulation not being an issue when they dip in the water strikes me as pretty solid also. And I don't picture a whole lot of induction going on there either, but I could be wrong. So in the spirit of "it's a floor wax AND a dessert topping", I was trying to reconcile how both of these could be correct. Short version is that perhaps plently of current is leaking, just not through the shorepower cord.

I very much doubt current is leaking through the cables described here.
However, is it possible that current is leaking elsewhere through the water on the shorepowerd boat, not through the big yellow shorepower cable, but via hull fittings and such (perhaps due to squirrely grounding setups)?

TRYING TO THINK MORE CLOSELY ABOUT WHAT IS INVOLVED:
I would *think* that a proper shorepower system would always have a Ground Fault Interrupter protected circuit. My layman's understanding of these is that the GFE can measure the current being supplied through the hot side of its outlet, and also measure the current returning to it and going to ground. If those are different, current is getting loose somewhere it shouldn't (perhaps from your hair-dryer to your bathtub drain!) and it cuts off the circuit to protect you.

I haven't ever installed a shore-power system, so bear with me as I make stuff up in lieu of actually doing any research, like reading Don's links. Imagine a boat with a standard 110V AC power outlet into which you can plug a household blender or TV or whatever. When at sea, I would expect a transformer/inverter that takes power from the motor's 12V DC alternator/generator-fed side of the world and produces 110V AC that you could use to run the blender. (As an aside, maybe dedicated generators supply 110AC more directly? But I would think they too would mostly be used for supplying the 12V DC house systems on board, like 12V cabin lights, radios, etc.)

But when docked with shore power, I would expect the 110V AC shorepower outlet would feed a transformer on the boat which would produce (mostly if not entirely) 12V DC power to the systems on the boat. I don't know if it would normally use a switch to also directly supply 110V AC directly from the shorepower feed to the outlet for the blender, or if the blender would be supplied by the shorepower being converted twice: first to the 12V DC world on board the boat, and then back to 110V AC through the same mechanism used to supply the blender at sea. Anyone know?

The reason for discussing all of this is to consider more closely what is going on aboard the neighbor boat with his shorepower system that we think is ruining our nice prop. I imagine that the pretty yellow cord that is plugged into the side of the neighbor boat is NOT leaking current. Further, if it were leaking any appreciable amount, I would expect a GFE to cut it off.

However, as long as it isn't cut off, it can supply oodles of power to other stuff on the boat, to the DC system and possibly to some AC systems as well. Even if a transformer isolates the the shorepower from all the stuff on the boat (preventing any DC current flow), it would seem like there is potential for lots of other stuff to happen, including stuff that involves the DC system onboard which is grounded to the motor and some through-hull metal fittings. As such, IS ANY OF THIS stuff a likely place for current leakage to the water that would wreck the prop next door? I would think that there were some subtleties to properly grounding all of this stuff, and that a do-it-yourselfer could easily botch the job.

Anyhow, trying to spark some further thought FWIW...

[txtaz]

Ghost, man, You can write. Care to help with my thesis? It's on the social implications of computers. Yeah get that, my advisor bought off on it for a science degree.

OK, we can assume democrats believe in the hole theory and republicans the electron theory. Now you Dems have a convention to attend so get busy.

And the theory of current draining from any other source than shore power would be difficult to accept. The shore power is stepped down and converted to 12-14V DC most likely by a battery charger. So if something in the hull were to leak current, it would not be enough to make a prop swiss cheese. Unless it's been sitting there for years.

Maybe we should look at the chemical side of this equation. It seems all props were aluminum. Were all in salt or brackish water? If so a small charge would cause erosion. I'm not sure but would it turn to aluminum oxide?

Let me go look....I'm back...Man you just gotta love Wikki

Al2O3 + 3 H2O + 2 NaOH → 2NaAl(OH)4 is Aluminum Oxide, strip it of Fe2O3 and you have Boxite which is a hard material used for manufacturing and production. But that still doesn't answer the question.

From Wikki:
Aluminium has nine isotopes, whose mass numbers range from 23 to 30. Only 27Al (stable isotope) and 26Al (radioactive isotope, t1/2 = 7.2 × 105 y) occur naturally; however, 27Al has a natural abundance of 99.9+ %. 26Al is produced from argon in the atmosphere by spallation caused by cosmic-ray protons. Aluminium isotopes have found practical application in dating marine sediments, manganese nodules, glacial ice, quartz in rock exposures, and meteorites. The ratio of 26Al to 10Be has been used to study the role of transport, deposition, sediment storage, burial times, and erosion on 105 to 106 year time scales.[5] Cosmogenic 26Al was first applied in studies of the Moon and meteorites. Meteoroid fragments, after departure from their parent bodies, are exposed to intense cosmic-ray bombardment during their travel through space, causing substantial 26Al production. After falling to Earth, atmospheric shielding protects the meteorite fragments from further 26Al production, and its decay can then be used to determine the meteorite's terrestrial age. Meteorite research has also shown that 26Al was relatively abundant at the time of formation of our planetary system. Most meteoriticists believe that the energy released by the decay of 26Al was responsible for the melting and differentiation of some asteroids after their formation 4.55 billion years ago.[6]

Could we be dealing with an isotope of aluminum do to absorstion of electrons no matter how small even from a dialectric field in salt water?

Da Taz<---OK, I just baffeled myself.:smash:

[BillG]

You can Wiki yourself to death, but the fact still remains that my prop was made a swiss cheese in about one week. I have had the boat in salt water for 36 years and have had aluminum, bronze and stainless props on it. The only time I have encountered the galvanic problem, was when the boat next to me had a battery charger hooked up for an extended length of time. This also not the first time I have heard of something like this happening.
Just my .02 cents.

Bill

[Ghost]

OK, we can assume democrats believe in the hole theory and republicans the electron theory. Now you Dems have a convention to attend so get busy.

Dems?! I apologize profusely in advance if I misunderstood the implication, but just in case, I feel the need to add some clarity (if not bathe): :)
1. Both major parties make me want to vomit, albeit one more than the other.
2. (in a related story, I believe in the "a-hole theory")
3. I'm a staunch libertarian of almost 20 years now

:) Okay, enough of that silliness. I don't want to further side-track the thread. Back to the swiss cheese.

Is it really true that the DC side of the world wouldn't produce enough current to hurt a prop? For example, suppose I set a battery charger (essentially a 13Volt source with a LOT of power available) on a raft next to someone's boat and plugged it in, without dipping the cord in the water. Then I took the the positive lead from the battery charger and stuck it into the nice, salty water. Wouldn't that pull in droves of negatively charged stuff (including needed electrons from your nearby prop, turning it to a pile of metal oxide)?

Aren't the voltage differences that make sacrificial anodes important significantly less than the 13V of a charger, and with FAR less power (energy per unit time) in the mix?

It's been ages since my physics textbooks, but it seems to make sense to me. The fact that Bill's prop got schwacked in such short time while a charger was on the boat next door seems particularly compelling, as this not only could put a steady and significant voltage source into the system, but also one with lots of energy to burn.

Does this make sense? What am I missing?


Could we be dealing with an isotope of aluminum do to absorstion of electrons no matter how small even from a dialectric field in salt water?

I completely agree that this happens--we see all sorts of relatively slow corrosion effects all the time--but I was thinking the reason for the abnormal rate here was the change in voltage and power with the charger being introduced.

Regards, and please keep the thoughts coming, I'm enjoying the discussion and am all about trying to understand, even if I sound cranky... :)

[txtaz]

Dems?! I apologize profusely in advance if I misunderstood the implication, but just in case, I feel the need to add some clarity (if not bathe): :)
1. Both major parties make me want to vomit, albeit one more than the other.
2. (in a related story, I believe in the "a-hole theory")
3. I'm a staunch libertarian of almost 20 years now

:) Okay, enough of that silliness. I don't want to further side-track the thread. Back to the swiss cheese.


Sorry if I was offensive. Just having some fun here.:angel:




Is it really true that the DC side of the world wouldn't produce enough current to hurt a prop?


Actually it can, however you would need ideal conditions and the situation we are discussing is not. I once shut down half a military base with a DC electromagnet I made. Yep I calculated my coil time constants wrong and drew hundreds of amps for a split second. It was not pretty.



Aren't the voltage differences that make sacrificial anodes important significantly less than the 13V of a charger, and with FAR less power (energy per unit time) in the mix?


:confused: I'm not sure what you are asking here. Obviously less potential, less power P(t)=I(t) * V(t).

The material anodes are made from is because they absorb electrons easier than other materials on the boat. Hence sacrificial. Zinc reacts to acids and alkaline substances easily...creating zinc oxide.

Da Taz<---Soon to be Dr. Taz...just gotta write that silly paper that is like a gazillion pages long.

[zelatore]

http://www.yachtsurvey.com/corrosion_in_marinas.htm

I refer you back to this link. I'm not a fan of everything David Pascoe writes, but he gets it pretty close on this and puts in laymen's terms.

The problem comes from the fact that the earth ground is tied to the DC ground.

As for the prop getting eaten up in a matter of weeks - it happens. I've had customers loose rudders, shafts, props, trim tabs...pretty much anything metal under water on a boat.

But the cause had nothing to do with the shore power cord drooping into the water. It was due to a wiring problem on the boat or the dock.

And that, gentlemen, is why sterndrives don't belong in saltwater.
(says the guy who sells only inboards :wink:)

SO- suggest the dock be kept clean and tidy as a housekeeping exercise or a safety exercise. That way the place looks better AND you don't have to worry about the local dock 'experts' complaining about a non-existent electrical problem.

Helmsman, what's our depth?

[DonziJon]

ONESUBDRIVER: "I spent alot of time as DOOW, COW, and in my early days, Helms/planes. Most of my time was spent in the room with the bomb" :shocking:

Wayne :)[/QUOTE]

"DOOW",... "COW": Just guessing: Was that "Diving Officer of the Watch"? Can't quite figure COW. Maybe "Conning Officer of the Watch"?? I was only Enlisted, and only Supported Submarines, and it's probably been way to long since I was in. Just wondering. John (OM1)

[zelatore]

I once shut down half a military base with a DC electromagnet I made.

And that makes me think, it's not a matter of 'if', but of 'how big' and 'how long ago' it was that you made your own tesla coil...

http://www.youtube.com/watch?v=FY-AS13fl30

Hmmmm...Oklahoma is pretty close to Texas....perhaps names/locations were changed to protect the guilty?

[txtaz]

Hmmmm...Oklahoma is pretty close to Texas....perhaps names/locations were changed to protect the guilty?

Now that was good and much MUCH bigger than I built.

Nope, I shut down Great Lakes Naval Facility just outside Chicago. My CO was very nice and understands technical experiments. I did however pull mid shift guard duty for a month and promised to never play with the electrical supply.

Dr. Taz<---Helmsman make heading one five zero, make speed one five knots, prepare for launch operations...OOOpppps, that was aircraft carrier speak. Yep played with them too. Subs are better people though IMO.

[onesubdrvr]

ONESUBDRIVER: "I spent alot of time as DOOW, COW, and in my early days, Helms/planes. Most of my time was spent in the room with the bomb" :shocking:

Wayne :)

"DOOW",... "COW": Just guessing: Was that "Diving Officer of the Watch"? Can't quite figure COW. Maybe "Conning Officer of the Watch"?? I was only Enlisted, and only Supported Submarines, and it's probably been way to long since I was in. Just wondering. John (OM1)[/quote]
COW - Chief of the Watch, you're right on DOOW,.... yeah, it's amazing how fast time slips away, last I knew I was in,....but it was actually 10 years ago.

:D
Wayne
<-- make heading 150 aye, make speed one five knots aye,... launch operations, are you kidding, I was on REAL subs, not "Boomers" lol :)

[Ghost]

Wow, this has been a sticky one! Further reading has shed some light--thanks for various links people have sent, which have been helpful.

I think the short version is that there are lots of different scenarios--LOTS. As a thread I think we've been bouncing around somewhat inadvertently--lots of ideas about what the reality is, when in fact we're probably talking about lots of different scenarios with different symptoms, different root causes, and different solutions. Makes sense given different people have run into different things.

As far as answers go, there is too much to relay and way too much I don't totally follow yet. I will be buying a whole book and reading further. Here are couple of useful notes, however, that seemed worth passing on:

1. Best I can tell, the properly insulated shore power line dipping in the water is not a problem.

2. Sounds like lots of problems are due to varied scenarios that involve:
- bad ground wiring,
- the fact that the drives and water can serve as paths to ground,
- differences between the land ground in the marina's electrical system and the onboard grounding,
- lack of proper isolation transformers between the AC shore power and DC systems onboard
- ordinary "car-battery" chargers, which often don't properly isolate the AC and DC sides either
- varying metals and quality thereof, the voltages they create, and all sorts of paths that current will take as a result, destroying metal in the process.

3. A lot of people who may be pretty expert in boats don't really understand the issues here (the big picture anyway), and sorting it out can be pretty complicated. Like, guys who write professionally about boat maintenance across many topics. I think this particular stuff is a black art even to many of them and many admit it outright.

4. In order to make sense out of what is going wrong somewhere, you most likely need to do some voltage/current/resistance measurements to figure out the voltage differences and where current is going.

One curiosity, the sort of scenario I speculated about earlier (quoted below for easy reference), sounds fundamentally correct in that "properly" set up (or improperly, depending how you look at it), this sort sort of thing is would have by far the most effect on materials in the shortest time. (I don't think I had the details dead on in my example, but the basic idea was right--dumping large amounts of current through the water with something like a charger would have huge effects in a short time.)

Illustrative of this is a related concept: Electrolytic Rust Removal, or ERR. Essentially, you take a DC voltage source (one example I found used a battery charger in fact) and stick the leads into an electrolyte bath, with the negative lead connected to a rusty piece you want to restore, and with the positive lead connected to a piece of sacrificial metal. In very short order, like 2 hours, the hydroxide (OH minus) ions in the rust are purged from the rusty piece, restoring a lot of its integrity, while the sacrificial piece becomes swiss cheese.

Okay, I have some book buying to go do... :doh:



Is it really true that the DC side of the world wouldn't produce enough current to hurt a prop? For example, suppose I set a battery charger (essentially a 13Volt source with a LOT of power available) on a raft next to someone's boat and plugged it in, without dipping the cord in the water. Then I took the the positive lead from the battery charger and stuck it into the nice, salty water. Wouldn't that pull in droves of negatively charged stuff (including needed electrons from your nearby prop, turning it to a pile of metal oxide)?

[txtaz]

1. Best I can tell, the properly insulated shore power line dipping in the water is not a problem.

2. Sounds like lots of problems are due to varied scenarios that involve:
- bad ground wiring,
- the fact that the drives and water can serve as paths to ground,
- differences between the land ground in the marina's electrical system and the onboard grounding,
- lack of proper isolation transformers between the AC shore power and DC systems onboard
- ordinary "car-battery" chargers, which often don't properly isolate the AC and DC sides either
- varying metals and quality thereof, the voltages they create, and all sorts of paths that current will take as a result, destroying metal in the process.



Ding ding ding...we have a winner. You are right on. However absolute ground and dc ground are most likely not at the same potential. The primary side and secondary side of a transformer (in the battery charger) is isolated. So to get them to be the same you would need to ground the battery to shore power. Not recommended.

Good housekeeping is the answer. Teach people to look for signs of corrosion, bad zincs, green copper, oxide on electrical connections etc. and then the problem should solve itself. Keep shore power cables clean, dry and out of the water.

Although this discussion has been fun, I have to say, Dad and I owned a salt water marina for 23 years, we have never had any problems such as this.

Dr. Taz<---Really miss writing off gas and expeses for company owned boats and cars.

[zelatore]

Ding ding ding...we have a winner. You are right on.

<---Really miss writing off gas and expeses for company owned boats and cars.

Yup. It's a very complicated situation and very few people actually understand it. I don't know it all ... I've never devoted the time to studying everything, only read about it here and there then moved on to the next issue.

As for write-offs....I'm all about that! Over the 4th I used my Donzi to run a couple clients from an anchorage to pick up an impellor for a gen and a racor for another gen. Bingo Baby! Buisness expense! I think I'll need to write of the blower install as well...after all, don't want to keep a client waiting!