Anodes- are they worth the money????

[larryjc]

Just got the boat out of the water for blacking at short notice as when in Liverpool I could suddenly see just how rusty it was getting. However when she was out it was quite clear that the anodes were only protecting the hull wthin about a metre of thier location consequently the bow and stern were fine but the sides well rusted up.  The anodes which were about 3 years old are still in goodish condition.

So whats the point??  To make them useful one would have to have them all down the sides about every metre.  Alternatively they aren't working properly but why?  They are in pairs probably because they were replaced but it wasn' worth taking the old ones off.  Is it possible that they are slightly different so are actually working against each other to a degree?  I understand the chemistry of how they work but can't reconcile that with what is actually happening.  Anyone else seen this effect?

[Robbo]

You need more anodes, they do only protect about a meter around.  It would be every other meter, not meter.  However on a narrowboat they are more likely to get knocked off.  The rear ones are prob more important as you have the stern / prob gear here.

Edited May 12, 2017 by Robbo

[larryjc]

I can understand then having them at the stern with all the different metals about but seems a waste of money to put them at the bow.   Anode manufacturers must be laughing all the way to the bank.

 

 

 

 

 

[Chewbacka]

7 minutes ago, larryjc said:

I can understand then having them at the stern with all the different metals about but seems a waste of money to put them at the bow.   Anode manufacturers must be laughing all the way to the bank.

 

 

 

 

 

It is an interesting point.  There are still quite a few old steel narrowboats that are not blacked very often, and certainly have never had zinga or 2 pack epoxy applied and maybe don't even have anodes which are still happily cruising the waterways.  But, I guess the ones that were not so lucky have long ago been scrapped.  So is it worth the risk???

 I suppose it is a bit like house insurance in that you only truly get your monies worth if the house burns down which normally is NOT what you want.

[Tony Brooks]

If bow anodes did not work they would not get eaten away so if the OPs anodes stay in good condition and unpitted for years and years then he can probably safely dispense with them. If not is it worth  the risk?

[bozlite]

Isn't it a misunderstanding, though, that anodes protect against rust? Or have I misunderstood?

[dor]

53 minutes ago, Tony Brooks said:

If bow anodes did not work they would not get eaten away so if the OPs anodes stay in good condition and unpitted for years and years then he can probably safely dispense with them. If not is it worth  the risk?

Unless they were zinc anodes meant for salty water.  I've seen them (mistakenly) fitted to narrowboats that have never been near salty water.

[Martin Megson]

Surely anodes protect against galvanic erosion not rust. 

[bozlite]

8 minutes ago, Martin Megson said:

Surely anodes protect against galvanic erosion not rust. 

That's what I've always thought ...

[Chewbacka]

46 minutes ago, Martin Megson said:

Surely anodes protect against galvanic erosion not rust. 

By fitting an anode you create a galvanic corrosion cell between the anode (Mg for fresh water) and the steel of the hull such that exposed steel which would normally rust (corrode) doesn't because the anode sacrifices itself (preferentially corrodes) so protecting the steel.  However as discussed previously, anodes only have a range of about a meter before their effect is too weak to be effective.

[larryjc]

So going back to my originl post if a boat is 12 meters long you should really have anode fitted every 2 metres, ie six each side or not bother at all. 

[Murflynn]

what is this new fashion to call 39.37" a 'meter' ??  ..............   even the OP has been suckered in to changing his spelling.

that spelling is only used by ignorant Americans who can't get their head around the MKS system (metric system).

we all know what meters are: they measure things like electricity or water flow;  the metre on the other hand is an largely imaginary concept that originally only existed in the form of a metal bar installed in a Parisian laboratory after the French Revolution.

Edited May 13, 2017 by Murflynn

[jddevel]

Is there anyway a "anode strip" could be run along the I suppose waterline to prevent galvanic corrosion. If it could don't think it would have to be that big. But then how to fix it and protect it I suppose. Just thinking. I`ve think I`ve  become obsessed with this problem!!!!!!

Or could I just Zinga a strip along the water line? How effective would that be maybe??

[rusty69]

2 minutes ago, jddevel said:

Is there anyway a "anode strip" could be run along the I suppose waterline to prevent galvanic corrosion. If it could don't think it would have to be that big. But then how to fix it and protect it I suppose. Just thinking. I`ve think I`ve  become obsessed with this problem!!!!!!

60ft magnetic anode? 

 

This time next years we will be Millionaires..... 

Edited May 13, 2017 by rusty69

[Captain Pegg]

8 minutes ago, Murflynn said:

what is this new fashion to call 39.37" a 'meter' ??  ..............   even the OP has been suckered in to changing his spelling.

that spelling is only used by ignorant Americans who can't get their head around the MKS system (metric system).

we all know what meters are: they measure things like electricity or water flow;  the metre on the other hand is an largely imaginary concept that originally only existed in the form of a metal bar installed in a Parisian laboratory after the French Revolution.

I think the fact you found it easier to express the number of inches in a metre as a decimal fraction answers your question neatly.

JP

[jddevel]

 

Just now, rusty69 said:

60ft magnetic anode?

Did suggest this possibility some time ago. However as was pointed out that introduces another metal to produce galvanization. Unless ofcourse you were being facetious?

[rusty69]

1 minute ago, jddevel said:

 

Did suggest this possibility some time ago. However as was pointed out that introduces another metal to produce galvanization. Unless ofcourse you were being facetious?

Yeah, i was joking. I suggested the idea some time back on another forum as a joke. Thought removeable magnetic anodes would  be good for bosts that didn't move much 

[jddevel]

But seriously could they be "attached" in some way with a good adhesive say every few feet but then how do you ensure the anode strip is in contact with the hull?? Just brainstorming with my silly head. Better get on and do something constructive or I`ll never get the boat in the water!!!!!

[WotEver]

12 minutes ago, jddevel said:

could they be "attached" in some way with a good adhesive say every few feet but then how do you ensure the anode strip is in contact with the hull?

I think the first part of your question answers the second part. It wouldn't. 

[Neil2]

18 hours ago, larryjc said:

Just got the boat out of the water for blacking at short notice as when in Liverpool I could suddenly see just how rusty it was getting. However when she was out it was quite clear that the anodes were only protecting the hull wthin about a metre of thier location consequently the bow and stern were fine but the sides well rusted up.  The anodes which were about 3 years old are still in goodish condition.

So whats the point??  To make them useful one would have to have them all down the sides about every metre.  Alternatively they aren't working properly but why?  They are in pairs probably because they were replaced but it wasn' worth taking the old ones off.  Is it possible that they are slightly different so are actually working against each other to a degree?  I understand the chemistry of how they work but can't reconcile that with what is actually happening.  Anyone else seen this effect?

When we had our boat grit blasted a couple of years ago it was quite startling how pristine the steel was in the immediate vicinity of the anodes compared to the rest of the hull.  I would agree they protect an area of no more than a metre.  But, the guy who did the blasting said it was the first clear example he had come across, bear in mind this is a 30 year old boat, he reckoned most of them you can't tell where the anodes were once the hull has been blasted back to bare metal.  Make of that what you will.

[jddevel]

Excuse my ignorance  but am I correct in believing that galvanic corrosion seems predominantly around the waterline? Or is just where you can see it`s obvious effect?

[Rick-n-Jo]

Corrosion near the waterline is just simple air/water enabled rusting, most likely here as the steel is in close proximity to both. Galvanic corrosion is electrical, either passive where two dissimilar metals are close together in an electrolyte fluid (like a battery) or actively caused by electric current flowing through the hull, for instance when the boats earth potential is not quite the same as another boat, or the metal piling. Galvanic can occur anywhere on the immersed hull where there is even a pinhole in the blacking, rusting is more likely near the surface where there is more oxygen available.

Edited May 13, 2017 by Rick-n-Jo
piss poor typing

[WotEver]

5 minutes ago, Rick-n-Jo said:

Corrosion near the waterline is just simple air/water enabled rusting, most likely here as the steel is in close proximity to both.

Plus if the blacking is only bitumen then it's probably been washed off at the waterline. 

[Rick-n-Jo]

3 minutes ago, WotEver said:

Plus if the blacking is only bitumen then it's probably been washed off at the waterline. 

Yes. Dissolves in diesel etc. I believe.

[BEngo]

22 hours ago, larryjc said:

I can understand then having them at the stern with all the different metals about but seems a waste of money to put them at the bow.   Anode manufacturers must be laughing all the way to the bank.

 

 

 

 

 

C'mon Larry.  Think back over the years to all those RNEC Manadon Properties of Materials lectures.  Bending and welding the steel stresses it and affects its structure so that parts of it are more cathodic than others. 

  I admit that the lectures didn't explain why anodes have a finite radius of action though.  I postulate that it is due to the natural and inevitable  resistance in  the electric circuit and the very low driving voltages from even Mg (alloy) anodes in fresh-ish water so after a certain distance from the anode the current falls too low to counteract the corrosion current.

N