lets talk about anodes.

[oldboot]

We all have sacrificail anodes on our outboards and the concept of how they work when immersed is quite straight forward and beyond argument.

But do they work when they are out of the water.

Ive scratched my head and tries to reason this..... but theonly thing thats going to prove it one way or another is....someone who has direct knoweledge.


so do they or don't they.

cheers

[tigermullet]

Anodes work out of water? No, they cannot.

[Hunt-N-Gather]

Also don't be afraid to take them off your motor and give them a clean up with a wire brush.
They work more efficiently if clean.

[Captain Seaweed]

No I dont think they do as air is not as dense as water and would have a very high resistance in the electrolytic part water plays in the corrosion process. I recon if it was super dense fog then maybe but not just air. This is only a guess.

Marty

[PinHead]

if you have Aluminium anodes then they will get a coating of AlO on them in the air. Not sure about zinc or magnesium ones.

[finga]

They work in the air.
The air around you has moisture and when combined with salts, which are also present on the motor and in the air, acts as an electrolyte.
The only question is rate of corrosion of the anode.
Easy way to show this is to take a piece of steel and grind any surface on it. Does it rust when it's done in Alice Springs??
Does it rust if you do it at the boat ramp at Viccy Point??
The answer is yes but the rate is considerably different between the two places because of the amount of moisture in the air and the amount of salts available for the reaction.

Would I be worried about taking anodes of the outboard to give them a clean with a manual wire brush or to give them a good old file up?
Nope. If I lived at Cleveland I'd have them back on pretty quickly and out here I could take my time and not worry much at all.
If you clean them use a file or manual wire brush. Don't use the wire brush on the angle grinder or bench grinder and always use a conducting grease when they go back on to get a good electrical bond between the electrode and the motor.
Also very important to have all those little bonding conductors around the motor in good nick too.

[hivalley]

Hi Oldboot,

This is what I believe.

To form a galvanic cell and start the galvanic corrosion process you need two dissimilar metals and an electrolyte. Depending where the two metals sit on the galvanic table one will be more noble than the other so one will be an anode and the other the cathode, when moisture (an electrolyte) is present a galvanic coupling of the two metals is formed, an electrolyte allows ion’s to flow from the anode to the cathode.

Go out to western Queensland or NSW and there will be old cars, tractors and all types of machinery laying around in paddocks many many years old and barely rusted, restores of old cars and machinery always search these areas for their projects because they know the low humidity and dry air has concededly slowed the galvanic corrosion process.

If you live on the coast close to a surf beach you will also know every thing is corroding before your eyes, even things kept under cover or in your garage will rust over time, this is because there is sufficient moisture from high humidity or sea spray in the air to act as an electrolyte and form a galvanic cell.

You do not have to submerge your outboard in water to start the galvanic process, salt water will be a better electrolyte than fresh, and coastal Australia will be better than central Australia to start the galvanic process, you will still get corrosion in dry climates but just at a different rate.

Cheers

[hivalley]

They work in the air.
The air around you has moisture and when combined with salts, which are also present on the motor and in the air, acts as an electrolyte.
The only question is rate of corrosion of the anode.
Easy way to show this is to take a piece of steel and grind any surface on it. Does it rust when it's done in Alice Springs??
Does it rust if you do it at the boat ramp at Viccy Point??
The answer is yes but the rate is considerably different between the two places because of the amount of moisture in the air and the amount of salts available for the reaction.

Would I be worried about taking anodes of the outboard to give them a clean with a manual wire brush or to give them a good old file up?
Nope. If I lived at Cleveland I'd have them back on pretty quickly and out here I could take my time and not worry much at all.
If you clean them use a file or manual wire brush. Don't use the wire brush on the angle grinder or bench grinder and always use a conducting grease when they go back on to get a good electrical bond between the electrode and the motor.
Also very important to have all those little bonding conductors around the motor in good nick too.

Finga, I posted a similar reply and only realised after I posted that you covered it with the same reasoning, thats the problem with typing with 2 fingers:undecided: By the time I get it posted every one has already covered it. Cheers:tongue:

[tigermullet]

I cannot see that moist air would be sufficient as an electrolyte. With dissimilar metals the galvanic process will progress at a certain rate in the presence of moisture but I doubt that the electrical bond between a hull or motor and the anode would be made just by moist air i.e., the anode wouldn't be giving any protection.

[hivalley]

I cannot see that moist air would be sufficient as an electrolyte. With dissimilar metals the galvanic process will progress at a certain rate in the presence of moisture but I doubt that the electrical bond between a hull or motor and the anode would be made just by moist air i.e., the anode wouldn't be giving any protection.


Hi tigermullet, do a google mate, just type humidity and galvanic corrosion, high humidity is an excelent electrolyte.

cheers.

[tigermullet]

Hi tigermullet, do a google mate, just type humidity and galvanic corrosion, high humidity is an excelent electrolyte.

cheers.

Thanks Hivalley. But if moist air is an excellent electrolyte wouldn't it be dangerous to walk under power cables on foggy days? I cannot see how the very weak current formed by dissimilar metals could be conducted via moist air to the anode. It's hard enough to get anodes to work in salt water. Unless properly placed they are next to useless.

The accepted practice for mono hulls is for the main group of anodes to be placed at 30% of the distance of the waterline length as measured from the stern toward the bow. With multi hulls, two groups are needed and equally divided, placing them at 20% and 52% of the waterline length as measured from the stern.

Our boat, a multihull, has the correct placement and nil corrosion after 12 years constantly in the water. Just for "extra" protection we bunged on a couple more anodes here and there. It was a waste - only the groups placed at 20% and 52% work. The other supplementary anodes show nil sign of working at all.

[TheRealAndy]

Oil rigs use aluminium anodes on the frames above the waterline.

[tigermullet]

I guess there must be a reason for using anodes above the waterline on oil rigs though I have no idea what the reason might be.

I don't really know much about anodes and protection of aluminium except for what is needed and has proved so effective on our boat. We have used stainless steel screws etc., above the waterline but would never consider mixing aluminium and stainless below the water line. There hasn't been any corrosion of aluminium in the areas where stainless fasteners have been placed but given that the whole boat is bonded the anodes must be providing sufficient protection.

[Stuart]

While on the subject of anodes, would it make sense to bolt a few on and around the place on a plat alloy hull. They work well on the an outboard so I can’t see why they wouldn’t work just as well on the hull itself.

Stu

[whiteman]

My mate is a chemical engineer and he reckons anodes on boats that are usually moving and stored on a trailer are probably unnecessary. He says that the chemical reaction needs water which is relatively calm around the metals. He also says that electrons like to work in a straight line so if the anode is to work it should be line of sight.

Is he right? My 10yo motor anode is like new on my trailer boat.

[finga]

He also says that electrons like to work in a straight line so if the anode is to work it should be line of sight.
So ask him how electricity is conducted on a wire that bends every which way possible??
When your getting down into molecular structure a straight line is a very short line (ie distance between two molecules) and an electron can be shot or pulled from any angle out of a molecule ie shot or pulled from any angle from the outer valence shell.
Electron transfer is better known as electricity in it's few forms ie AC, DC and static.

Something of interest too is that pure water is an insulator.
It takes an impurity such as a salt (not just the sodium chloride salt but any chemical salt) to make water conductive.

[SgBFish]

My 10yo motor anode is like new on my trailer boat.

If you use it in salt water then something else is depleting electrons!
I take it its an aluminium boat.

[TheRealAndy]

While on the subject of anodes, would it make sense to bolt a few on and around the place on a plat alloy hull. They work well on the an outboard so I can’t see why they wouldn’t work just as well on the hull itself.

Stu

An anode on any metallic hull will be benificial. If you own a plate boat, chances are the anodes on your outboard will be doing the job! So as long as your outboard has a good electrical connection to your hull, and you keep the anodes on your outboard in good nick, you should not need any more anodes on the hull itself.

[tigermullet]

An anode on any metallic hull will be benificial. If you own a plate boat, chances are the anodes on your outboard will be doing the job! So as long as your outboard has a good electrical connection to your hull, and you keep the anodes on your outboard in good nick, you should not need any more anodes on the hull itself.


Plus it is not so easy to attach anodes to an aluminium hull. We had threaded rod welded to the hull at the correct positions and used large rudder anodes held in place by nylon nuts - note, nylon not nyloc. Drag was not a real concern for us but on a fast boat the shape of anodes could interfere.

[oldboot]

This is why I said..I had tried to reason the matter.....things like this never work like pure theory, and there is always more to it that how the simple explanation says.

As I said it is plain and clear how it all works with the main body and the sacrificial anode both immersed.

After that it becomes a matter for much discussion...which will never prove anything.

But a film of water on the surface, or perhaps a spray or mist......hmmmmm

What i am thinking about is.....If there is a possible benifit to bolting a couple of anodes to the chasis of my 4WD.

Now it is plan also that galvanic protection works on a short path basis.....otherwise we would not bother galvanising or plating land bassed structures that will never be immersed.......but that is usually accepted as the sacrificial coating protecting a bare portion of matal immediately adjacent...like a scratch.

But would it carry further than that.

cheers

[TheRealAndy]

This is why I said..I had tried to reason the matter.....things like this never work like pure theory, and there is always more to it that how the simple explanation says.

As I said it is plain and clear how it all works with the main body and the sacrificial anode both immersed.

After that it becomes a matter for much discussion...which will never prove anything.

But a film of water on the surface, or perhaps a spray or mist......hmmmmm

What i am thinking about is.....If there is a possible benifit to bolting a couple of anodes to the chasis of my 4WD.

Now it is plan also that galvanic protection works on a short path basis.....otherwise we would not bother galvanising or plating land bassed structures that will never be immersed.......but that is usually accepted as the sacrificial coating protecting a bare portion of matal immediately adjacent...like a scratch.

But would it carry further than that.

cheers

Have a read here. This is probably the best site you will find with regards to corrosion. http://corrosion-doctors.org/Car/carCP.htm

In short, an anode will not work out of water. This is a pretty broad assumption and is not entirley correct, but sufficiently true for 99% of applications on this forum.

[finga]

Have a read here. This is probably the best site you will find with regards to corrosion. http://corrosion-doctors.org/Car/carCP.htm

In short, an anode will not work out of water. This is a pretty broad assumption and is not entirley correct, but sufficiently true for 99% of applications on this forum.
Gees I don't know about that.
Some pretty broad assumptions would have to be made to make a statement like that like low relative humidity levels, low concentrations of dissolvable salts in the soil or air or even some assumptions of how well somebody cleans stuff otherwise we're all just wasting money on getting stuff galvanised as there is no need for it.
The zinc on boat trailers is only a huge skinny sacrificial anode.
The zinc on the roof is only a huge, thin sacrificial anode.
Galvanising is only the process of covering something with a thin anode.

As an experiment put a saucer of common cooking salt on the vanity when a teenage girl has a hot shower.
After the shower have a gander at the saucer. There should be droplets of water very much present. This is because salts are hygroscopic. They suck moisture from the air and the reason the salt goes all cluggy in the salt shaker.

The same happens to a boat or boat trailer or car or the roof if there are salts present. The salt sucks the moisture from the air and the resultant salty solution is conductive and is the start of the redox reaction commonly known as corrosion.
These salts could be environmental (ie sea spray or dust) from where the item is stored or the salts could be left over from cleaning after been in the briney and when combined with moisture the salts have absorbed from the air there is a formula for corrosion.

Salts are used for controlling humidity by there ability to 'suck' out moisture from the air.

So seeing that most of Australians live in areas with a reasonably high relative humidity that's reasonably close to a great source of salt (ie ocean) the chances of something rusting is pretty good. Hence why we depend on galvanising (remember the zinc from galvanising is just a really thin anode that covers a large area of the item) and like processes to restrict corrosion.

But if you live in Alice Springs were the relative humidity is really low then an anode would really not do too much.

[TheRealAndy]

Gees I don't know about that.
Some pretty broad assumptions would have to be made to make a statement like that like low relative humidity levels, low concentrations of dissolvable salts in the soil or air or even some assumptions of how well somebody cleans stuff otherwise we're all just wasting money on getting stuff galvanised as there is no need for it.
The zinc on boat trailers is only a huge skinny sacrificial anode.
The zinc on the roof is only a huge, thin sacrificial anode.
Galvanising is only the process of covering something with a thin anode.

As an experiment put a saucer of common cooking salt on the vanity when a teenage girl has a hot shower.
After the shower have a gander at the saucer. There should be droplets of water very much present. This is because salts are hygroscopic. They suck moisture from the air and the reason the salt goes all cluggy in the salt shaker.

The same happens to a boat or boat trailer or car or the roof if there are salts present. The salt sucks the moisture from the air and the resultant salty solution is conductive and is the start of the redox reaction commonly known as corrosion.
These salts could be environmental (ie sea spray or dust) from where the item is stored or the salts could be left over from cleaning after been in the briney and when combined with moisture the salts have absorbed from the air there is a formula for corrosion.

Salts are used for controlling humidity by there ability to 'suck' out moisture from the air.

So seeing that most of Australians live in areas with a reasonably high relative humidity that's reasonably close to a great source of salt (ie ocean) the chances of something rusting is pretty good. Hence why we depend on galvanising (remember the zinc from galvanising is just a really thin anode that covers a large area of the item) and like processes to restrict corrosion.

But if you live in Alice Springs were the relative humidity is really low then an anode would really not do too much.

The difference between galvanisation and a sacrificial anode as per you outboard is that the former covers the entire area as you say. Remember, for a sacrificial anode to work the must be a circuit (ie the electrons must be able to flow back to the less noble metal), and with out some form of electrolyte this is not possible. Try measuring the resistance of moist salty air. If your entire surface is covered in the anode its a different story.

Furthermore, galvanising not only acts as an anode, it is also form a protective coating which prevents corrosion.

The best way to prevent corrosion is by using protective coatings.

[finga]

So why does a car rust in the shed at Victoria Point and not Alice Springs?
Both examples are 'dry'.

I will grant that for the anode to work for an entire boat (even in water) there needs to be some serious equipotential bonding to be done and the electro-mechanical join between the outboard and the anode needs to be good (most boats would fail this I reckon) otherwise there's is not much protection happening..at all.

[TheRealAndy]

So why does a car rust in the shed at Victoria Point and not Alice Springs?
Both are 'dry'.

Dont you hate it when you type up a response and then accidently refresh the browser?

Its been a while since I have consulted my materials books from uni, so if you are reading this and youare a chemist please pipe in.

There is many things that cause corrosion, but at a guess I would say its one of 2 things (or both).

Where the is an oxygen imbalance at the edge of a of water molecule(s). You can often see this on old plate ships, where there is a concentration of corrosion at the waterline. Another good example is a metal pipe in concrete(this time is an oxygen imbalance thanks to the concrete as opposed to water).

So natually where there is more water in the air there will be more corrosion. The corrosion cells will be very local however, and to use cathodic protection would require an anode to be placed between the metal and the electrolyte (ie molecule of water) which is not possible.

Corrosion can also occur with different ion concentrations, ie at grain boundaries in the metal. I am only guessing on this one but I reckon it could also be responsible.

I am sure there are other forms of corrosion occuring too, but buggered if I can remeber them.


Dont quote me on the low level chemistry on this either! I did a subject on material science and a subject on corrosion science in uni, but that was over 10 year ago now!!

[TheRealAndy]

Just dug out one of my materials books, it says the following about uniform attack, or uniform corrosion:

Uniform attack is a form of electrochemical corrosion that occurs with equivelent intenstity over the entire exposed surface and often leaves behind a scale or deposit.

It then goes on to say that:

Some familiar examples include general rusting of steel and iron...

It gets complex after that, but suggest that anodic regions are formed from things like forming or machining, or the things I mentioned earlier such as oxy depletion etc.

However, all things in common are water droplets! So goes goes to reaffirm that high humidity accelerates the process. Add in salts of any form and the problem gets worse.

[finga]

It gets complex after that, but suggest that anodic regions are formed from things like forming or machining, or the things I mentioned earlier such as oxy depletion etc.

That would be due to dislocation or work hardening in the machining process. A slightly different crystal of the parent material is evident after machining.

So you need water for corrosion to happen and it gets worse when salts present themselves.
Isn't water and salt an electrolyte and the higher the humidity and amount of salts create a better electrolyte and for an anode to work you need an electrolyte?
That's one reason why I use a conducting paste when I put the anodes on.
It gives a better contact with the alloy where the electro-mechanical bond cannot be broken easily which makes the anode work better and lessens the chance of a high resistance joint between the anode and alloy if the anode decided to do the nasty in the join.
It reduces the need for an electrolyte to get the ionic exchange between anode and alloy happening. The paste is the electrolyte.

I have been meaning to get out the old chemistry books too but they're in Brisbane and I'm not.
Working from memory...so I hope it's not too bad.

[TheRealAndy]

That would be due to dislocation or work hardening in the machining process. A slightly different crystal of the parent material is evident after machining.

So you need water for corrosion to happen and it gets worse when salts present themselves.
Isn't water and salt an electrolyte and the higher the humidity and amount of salts create a better electrolyte and for an anode to work you need an electrolyte?
That's one reason why I use a conducting paste when I put the anodes on.
It gives a better contact with the alloy where the electro-mechanical bond cannot be broken easily which makes the anode work better and lessens the chance of a high resistance joint between the anode and alloy if the anode decided to do the nasty in the join.
It reduces the need for an electrolyte to get the ionic exchange between anode and alloy happening. The paste is the electrolyte.

I have been meaning to get out the old chemistry books too but they're in Brisbane and I'm not.
Working from memory...so I hope it's not too bad.

The problem is that you need the sacrifical anode IN the corriosion cell for it to be effective, so with uniform corrosion, you would need a little zinc anode in every molecule of water. When your whole surface is in the electrolyte things become a little easier.

BTW, its for this exact same reason that electronic rust prevention cannot work. You cant just force electrons into a metal, its not possible. Basic physics prevents this from happening. It like trying to light up a light bulb by only connecting one wire. Exact same principle.

[finga]

So what's the difference between a covering of an electrolyte that's caused by humidity (when it's a high humidity it has a high concentration of water that goes everywhere that's not airtight) and a covering of electrolyte from submersion? In both cases the parent material is covered by an electrolyte.

Granted the submersion would be a better proposition for the anode to work due to less resistance in the electrolyte but the higher the humidity the lower the resistance as well (out of water that is) especially if the boat was used in the briney and was not washed too well remembering that sodium chloride is highly hygroscopic and will suck moisture from the air to make an electrolyte.
Rememeber also that there is an accepted correlation between conductance (and capacitance) and humidity and is how electronic hydrometers work.
They're both covering the alloy or base metal with an electrolyte but the effectiveness, or strength, of the humidity based electrolyte greatly depends on salt concentrations and moisture concentrations.

An example of this electrolyte caused by environmental conditions of humidity and atmospheric available salt is the good old 11kV (or higher) insulator on power poles.
Along the coast there is always an insulator breaking down and flash overs happening as compared to an insulator in Alice Springs.
You can usually hear one crackling if you go for a walk near a surfing beach where power lines are close by.

[TheRealAndy]

So what's the difference between a covering of an electrolyte that's caused by humidity (when it's a high humidity it has a high concentration of water that goes everywhere that's not airtight) and a covering of electrolyte from submersion? In both cases the parent material is covered by an electrolyte.

Granted the submersion would be a better proposition for the anode to work due to less resistance in the electrolyte but the higher the humidity the lower the resistance as well (out of water that is) especially if the boat was used in the briney and was not washed too well remembering that sodium chloride is highly hygroscopic and will suck moisture from the air to make an electrolyte.
Rememeber also that there is an accepted correlation between conductance (and capacitance) and humidity and is how electronic hydrometers work.
They're both covering the alloy or base metal with an electrolyte but the effectiveness, or strength, of the humidity based electrolyte greatly depends on salt concentrations and moisture concentrations.

An example of this electrolyte caused by environmental conditions of humidity and atmospheric available salt is the good old 11kV (or higher) insulator on power poles.
Along the coast there is always an insulator breaking down and flash overs happening as compared to an insulator in Alice Springs.
You can usually hear one crackling if you go for a walk near a surfing beach where power lines are close by.

You summed it up perfectly. We are talking about .5 to 1.5V here (refer to the galvanic series and anodic index -> http://en.wikipedia.org/wiki/Galvanic_corrosion), not 11kv!! 11kv jumps from molecule to molecule, 1.5V doesn't. Same as trying to use your multimeter to measure the resistance of humid air (except thats 9 volts).

At the end of the day, all you are doing with a sacrificial anode is creating a battery cell. If you suck all the acid out of your car battery it wont work either. The principle is exactly the same.

[Reefmaster]

Interesting topic this one. I have two anodes fitted to the lower part of my transom which Riptide alloy boats fit as a standard option. After going to such great lengths for a paint job I wanted maximum protection to avoid/prevent corrosion in my boat. The paint job is now over 2 years old and I have had minimal problems with corrosion under the paint. Some small spots here and there which have been fixed straight away to avoid it getting any worse.


My anodes are mounted to the non painted surface and have got a powdery look to them so they must be doing something.

Can't say for sure whether having anodes on a boat is 100% effective but seems like a small price to pay as far as I'm concerned.

Regards
Greg

[TheRealAndy]

Actually, the wikipedia link has an excellent photo of anodes not working!! Take a look at the aluminium anodes on what looks like an oil rig http://en.wikipedia.org/wiki/File:Anodes-on-jacket.jpg

You can clearly see that all the metal is still uniformly rusting!! Not sure what the purpose of those anodes are, but I am guessing they are there for when the structure gets submersed due to bad weather or the like.

[TheRealAndy]

Interesting topic this one. I have two anodes fitted to the lower part of my transom which Riptide alloy boats fit as a standard option. After going to such great lengths for a paint job I wanted maximum protection to avoid/prevent corrosion in my boat. The paint job is now over 2 years old and I have had minimal problems with corrosion under the paint. Some small spots here and there which have been fixed straight away to avoid it getting any worse.


My anodes are mounted to the non painted surface and have got a powdery look to them so they must be doing something.

Can't say for sure whether having anodes on a boat is 100% effective but seems like a small price to pay as far as I'm concerned.

Regards
Greg

If the anodes have that powdery look then they are doing their job. Whilst using a protective coating on the boat insulates it from galvanic corrosion, it also prevents anodes from working. If you have some exposed aluminum then that is a good thing. As you said, once the paint starts to bubble, get in and fix it straight away. If left to its own devices it will continue to do damage.

THere was an excellent case of this years ago, where a crude oil line ruptured. The pipe was covered in a protective insulated coating which prevented the cathodic protection from working. The pipe rusted out below the coating and ruptured.

[finga]

Why is there around 220mV (by two different multimeters) between my hull and my anode if there is no perceived electrolyte like immersion in water??
There has to be an electrolyte to have a galvanic cell hence the 220-230mV reading on the multimeters.
It may be a weaker galvanic cell then under optimum conditions but it's there.

No battery at all in the boat as well.

[Spaniard_King]

Scott,

I would be rushing out to drive an earth stake into the ground and hooking up some decent cables to the hull before you electrocute some poor soul:grin: :grin: :grin: :smiley:

[TheRealAndy]

Why is there around 220mV (by two different multimeters) between my hull and my anode if there is no perceived electrolyte like immersion in water??
There has to be an electrolyte to have a galvanic cell hence the 220-230mV reading on the multimeters.
It may be a weaker galvanic cell then under optimum conditions but it's there.

No battery at all in the boat as well.


Probably leakage or noise. Put the boat in a faraday cage! Even at .2v you still dont have a cell. According to the anodic index you need greater than .6v to prevent galvanic corrosion.

[finga]

Scott,

I would be rushing out to drive an earth stake into the ground and hooking up some decent cables to the hull before you electrocute some poor soul:grin: :grin: :grin: :smiley:
That enough lip from you young fella...you just wait until I see you again. Cattle prodder for Garry :wink:

Probably leakage or noise. Put the boat in a faraday cage! Even at .2v you still dont have a cell. According to the anodic index you need greater than .6v to prevent galvanic corrosion.
How about I just build a Farady cage and a Van de Graaf and stand in it and take some pictures?? Sounds like more fun then chucking the boat in. Actually I reckon it be would be pretty good pictures with 'Junior' in there too and sit in it. Just have to remember to take any graphite rods out :smiley:

[Bros]

Anodes don't work in air but they do work in water or the earth.

[Bros]

Why is there around 220mV (by two different multimeters) between my hull and my anode if there is no perceived electrolyte like immersion in water??
There has to be an electrolyte to have a galvanic cell hence the 220-230mV reading on the multimeters.


If you use this example yes the anode will work but only over the contact area between the anode and cathode but not for the rest of the metal so if you want to say they work out of the water the answer is yes but they don't work in the same manner as when they are immersed in an electrolyte.

Your multimeter is correct just hose the anode to metal junction and the Mv reading will increase

[finga]

Yeah, OK. You've all convinced me they don't work effectively or efficiently out of water.
And the exercise has worked my old brain a bit :)
But if the conditions of very high humidity (around the 90%) and a layer of salt was there do they work??

So why did I get a bunny?? I did the old : and then a ) and got a bunny. Strange??

[finga]

If you use this example yes the anode will work but only over the contact area between the anode and cathode but not for the rest of the metal so if you want to say they work out of the water the answer is yes but they don't work in the same manner as when they are immersed in an electrolyte.

Your multimeter is correct just hose the anode to metal junction and the Mv reading will increase
Oh hang on. I just read this bit. Beauty :cheesy:
So if the conditions of high humidity and a layer of salt left over from not washing so good then would that satisfy the conditions for the anode to work a bit better??

[Bros]

Oh hang on. I just read this bit. Beauty :cheesy:
So if the conditions of high humidity and a layer of salt left over from not washing so good then would that satisfy the conditions for the anode to work a bit better??

On second thoughts that might not have been entirely correct. The Mv reading shouldn't change but the external current flow will as you are adding more electrolyte to the battery as that is all it is a battery.

When the anode is immersed this external current will flow through the salt water and the less noble metal will corrode.

[TheRealAndy]

Yeah, OK. You've all convinced me they don't work effectively or efficiently out of water.
And the exercise has worked my old brain a bit :)
But if the conditions of very high humidity (around the 90%) and a layer of salt was there do they work??

So why did I get a bunny?? I did the old : and then a ) and got a bunny. Strange??

If the entire surface of the boat and the anode was covered in salt (sodium chloride version) and given that sodium chloride is hygroscopic and will absorb the water out of the air it is definitely possible. Take for example a gel battery, it uses a desiccant to hold the electrolyte in a more solid form. As long as that cell has a voltage greater than the corrosion potential of the aluminium then it will work.

[BaitThrower]

What I want to see is some kind of anode system that works on gal trailers to stop them rusting :)

[Bros]

What I want to see is some kind of anode system that works on gal trailers to stop them rusting

You have it, it is the zinc that it is dipped in and it doesn't last forever in a salt environment.

[TheRealAndy]

You have it, it is the zinc that it is dipped in and it doesn't last forever in a salt environment.

OR paint. so many people over look paint. I have had many trailers that were not galvanised. I just painted them, and kept painting them. Bored one weekend and have some leftover paint, then slap it on. Might not look pretty, but it works

[Mister]

We all have sacrificail anodes on our outboards and the concept of how they work when immersed is quite straight forward and beyond argument.

But do they work when they are out of the water.

Ive scratched my head and tries to reason this..... but theonly thing thats going to prove it one way or another is....someone who has direct knoweledge.


so do they or don't they.

cheers

No No No No No