Corrosion questions - confused with opinions...!

[Chris Pink]

Wouldn't marinas be the worst place to run this kind of system? If everyone had their hulls electrified wouldn't you end up in a voltage war to ensure your boat remained cathodic?

 

From "complexity? cost? or what?" you omitted the most likely reason: "because it's unnecessary". Given that corrosion in fresh water doesn't appear to be much of an issue, isn't this using a sledgehammer to crack a nut?

 

You are imposing your own point of view on a technical question. It is your point of view that "Given that corrosion in fresh water doesn't appear to be much of an issue", my contention is that it might be an issue, anecdotal evidence suggests that it is, there seems to be no objective evidence either way on this forum

 

Except that Don's professional and well tested system implies there could well be a problem.

 

So I'll rephrase my question;

 

if you were considering using a GI or an IT then why not consider an impressed current DC system?

 

If my reading is correct then the only thing at risk is the anode that is part of that system and could be built into the pontoons.

Edited November 10, 2011 by Chris Pink

[Albion]

Come on..!! There would have to be a serious electrical leakage for that to be happening.

It's nothing to do with stray currents, it is all to do with the relatively strong electrolyte and the materials of the anode and cathode forming a battery cell, in effect.

Roger

[Chris Pink]

It's nothing to do with stray currents, it is all to do with the relatively strong electrolyte and the materials of the anode and cathode forming a battery cell, in effect.

Roger

 

If that were so then the discussion wouldn't be about GI and ITs

[Evo]

The most salient point..to this discussion!!

 

Saline and brackish water in esturine muds is a great electrolyte considerably enhancing corrosion whereas pure rainwater in inert sand is benign

 

Canals dont get much closer to BENIGN than that..!!

 

 

It's nothing to do with stray currents, it is all to do with the relatively strong electrolyte and the materials of the anode and cathode forming a battery cell, in effect.

Roger

 

A magnesium lump in salt water will not fizz...what the hell were they parked next to....galvanic corrosion does not fizz. By fizz I mean bubble away visibly. Its a relatively slow process, and Yes, I know how it works, its a pretty weak battery though isn't it, not exactly up to lead acid strength even in salt water.

[Albion]

 

A magnesium lump in salt water will not fizz...what the hell were they parked next to....galvanic corrosion does not fizz. By fizz I mean bubble away visibly. Its a relatively slow process, and Yes, I know how it works, its a pretty weak battery though isn't it, not exactly up to lead acid strength even in salt water.

 

I quote from the M G Duff website, and they might know a little about anodes:

 

Should a vessel move into fresh water for more than two weeks MGDUFF recommend that an alternative anode system is used suitable for fresh water situations. Magnesium Anodes on the other hand have a much higher driving voltage than zinc or aluminium making them highly suitable for use in Fresh Water, they will however become very active in salt water where they will probably only last a matter of months. Protected surfaces can build up a layer of off white calcareous deposit which will be difficult to remove.

Magnesium anodes are not designed for prolonged use in sea water and if you are taking your boat into a salt water location for more than seven days (Fourteen days in any one year) you should consider changing the anodes.

I would suggest that when a battery (anode, cathode and electrolyte) becomes Quote very active Unquote and Quote last a matter of months Unquote you might see evidence of that activity as I have suggested

 

Roger

[Nine of Hearts]

Except that Don's professional and well tested system implies there could well be a problem.

 

Only if you bury your boat in salt-water laden earth, though. He did state that fresh water was benign.

 

And you seem to suggest that if someone posits a problem for which the only supporting evidence is anecdotal (at best), that the positions as to whether that problem exists or not are entirely equal??? You do have a sock tied around your gateposts to keep away the elephants, don't you?

Edited November 10, 2011 by Nine of Hearts

[Doorman]

Canals dont get much closer to BENIGN than that..!!

 

 

I'm sorry Evo, but that's a generalisation. A stretch of the Middlewich Arm of the Shroppie

is reputed to be brackish, hence the need to overplate boats that had been moored in that particular area.

 

Mike

Edited November 10, 2011 by Doorman

[Evo]

I dont care what happens in salt water really. I think we all agree salt water is a bitch to most metals.

 

Our boat is in the heart of the midlands in a fresh water canal fed by rainwater reservoirs and rivers. For demonstrating galvanic corrosion then an English inland waterway canal is posibly the worst naturally occurring electrolyte I can think of.

 

 

Who disagrees that our canal water is a crap electrolyte..? By agreeing you are dismissing significant galvanic corrosion.

 

REFUTED...!!!!

[Timleech]

I'm sorry Evo, but that's a generalisation. A stretch of the Middlewich Arm of the Shroppie

is refuted to be brackish, hence the need to overplate boats that had been moored in that particular area.

 

Mike

 

When I first came on the canals, boats floated noticeably higher around Middlewich than elsewhere

No, I'm not making it up.

 

Tim

[Albion]

A magnesium lump in salt water will not fizz...what the hell were they parked next to....galvanic corrosion does not fizz. By fizz I mean bubble away visibly. Its a relatively slow process, and Yes, I know how it works, its a pretty weak battery though isn't it, not exactly up to lead acid strength even in salt water.

 

 

I dont care what happens in salt water really. I think we all agree salt water is a bitch to most metals.

 

You now say that you don't care about an illustration of what I saw in salt water and yet you openly challenged my assertion that I had seen bubbling from fresh water anodes (Magnesium) in a salt water environment. It cannot be a Quote relatively slow process Unquote if it reduces a lump of Magnesium weighing several kilos to virtually nothing in a matter of months and it is recommended that you don't keep a fresh water boat in salt water for more than 14 days per year total.

I also knew a guy who bought a share in a share-boat scheme from a builder who also asserted that fitting anodes to canal boats was a waste of time. The first time the boat was removed from the water for blacking the share owners decided that,despite what the builder had said, due to what they had seen they would have anodes fitted after all.

Roger

[bigcol]

Why don't somone do a simple test with a meter

 

With a meter put one end on you boat and the other on a metal ring or cleat

 

A). without shore power

With shore power connected

C). With shore power connected with GI connected

 

At willowbidge marina perhaps 20 boats online moorings all plugged in, the test above that was done to 3 boats was alarming

 

And yes one boat seemed to fizzing very small bubbles when connected at his bow and stern, when disconnected nothing!! This is what started it all, and why some of us bought GI

 

Why is it that narrow boats require welding in their lives, especially around the waterline

 

GRP boats have anodes on them on the stern gear, and if no anodes the outdrives, stern gear, gets eaten away, fact!

 

Be nice for somone do the simple test with a mtr and the proof will be in the pudding so to speak

 

Col.

[Evo]

Dying freshwater algae or you have an electrical leak.

Edited November 10, 2011 by Evo

[Timleech]

 

Galvanic corrosion on such systems was unpredictable and could be devastating. When a new underground tank was installed in an existing installation it often failed ahead of the older. thinner tanks. Evidently new steel is more anodic so they sacrifice themselves to prolong the lives of their elders!

 

Sounds very much like my description of different batches of steel on the same boat affecting one another.

 

The ground, and ground water conditions, considerably effect the corrosion stress. Saline and brackish water in esturine muds is a great electrolyte considerably enhancing corrosion whereas pure rainwater in inert sand is benign

Cheers Don

 

Canal water is not the same as 'pure rainwater in inert sand'

 

Tim

[Albion]

Dying freshwater algae or you have an electrical leak.

 

Yep, it could have been heavy-breathing shell fish that just happened to have attached themselves to the hull in exactly the same position as the anodes were mounted, I'll give you that one.

From memory and knowing where the land-line connector was on the boat (and I should do as I bought the second build of that type of boat subsequent to the visit to that Southampton Boat Show) a connected land-line was unlikely as it would have provided a trip hazard for visitors clambering all over the boat. It is possible but I don't remember one and think it was unlikely during visitor hours.

Roger

[Evo]

I'm back to the beginning..!!

 

I know corrosion occurrs.!!!.....remember steel rusts (oxidises) in just air and water, no fancy electrical process necessary.

 

I know what galvanic corrosion is and I know its huge on alum outboards in sea water, or steel boats in sea water.

 

I have dismissed galvanic corrosion as being any sort of a big deal in canals because the electrolyte necessary for the process is IMO - and easily chemically proven - very poor.

 

I have not dismissed electrical leakage from somewhere causing an issue, I have only questioned the function of a sacrificial anode in this scenario. No one as yet has touched on this.

 

Canal water is not the same as 'pure rainwater in inert sand'

 

I didn't say it was, I hinted it wasn't a million miles away from it.

[bigcol]

Re Albions post re having seen anodes fizz

 

Having a chat with the owner of once a fizzing boat at the bow and stern before he fitted a GI, and now it don't make bubbles anymore

 

Thanks to Albions post we've realised his anodes are mounted right at the bow and right on the stern, so it shows that the anodes were doing their job it wasn't the hull but the anodes!

 

Because if they weren't there, then it would have been his hull surely??

 

Which equals hull corrosion!!

 

Col

[Evo]

Yep, it could have been heavy-breathing shell fish that just happened to have attached themselves to the hull in exactly the same position as the anodes were mounted, I'll give you that one.

From memory and knowing where the land-line connector was on the boat (and I should do as I bought the second build of that type of boat subsequent to the visit to that Southampton Boat Show) a connected land-line was unlikely as it would have provided a trip hazard for visitors clambering all over the boat. It is possible but I don't remember one and think it was unlikely during visitor hours.

Roger

 

 

It didn't have to be you with the leak did it...not at the Southampton boat show.

 

Col..if the guy fitted a GI and it solved the problem then surely he had an eletrical leak of sorts

Edited November 10, 2011 by Evo

[Albion]

I'm back to the beginning..!!

 

I know corrosion occurrs.!!!.....remember steel rusts (oxidises) in just air and water, no fancy electrical process necessary.

 

I know what galvanic corrosion is and I know its huge on alum outboards in sea water, or steel boats in sea water.

 

I have dismissed galvanic corrosion as being any sort of a big deal in canals because the electrolyte necessary for the process is IMO - and easily chemically proven - very poor.

 

I have not dismissed electrical leakage from somewhere causing an issue, I have only questioned the function of a sacrificial anode in this scenario. No one as yet has touched on this.

 

Ok so having accepted that the process occurs in salt water (an active electrolyte) with a Magnesium (fresh water)anode and steel hull it isn't difficult to accept that the same process occurs (galvanic action) but much slower , with the same materials, in canal water (a much, much less active electrolyte, but nevertheless an electrolyte still).

However, from my understanding of the processes involved I'm not sure how effective anodes would be if you are concerned only with corrosion caused by stray earth leakage current from land-line connections (or nearby land-line connections) <electrolytic corrosion>. I have always had my boats fitted with Isolation Transformers to guard against this problem.

 

To answer your other point about other boats having been connected, yes that's possible I guess if the boat that I was looking at had been moored to a metal pontoon and in electrical connection to it. Anecdotally, but only second-hand, I have been told that fresh water boats crossing the Etang de Thau (south of France crossing to get to the Midi and salt/brackish water) also display bubbling anodes during the crossing. If that is the case, and I only have it second-hand, then they won't be connected to a land-line, nor in the vicinity of another boat that is.

Roger

Edited November 10, 2011 by Albion

[Evo]

Its another pointless argument...easily resolved.

 

Someone go dangle a magnesium anode in a harbour somewhere. Wear your goggles though wont you.

 

 

However, from my understanding of the processes involved I'm not sure how effective anodes would be if you are concerned only with corrosion caused by stray earth leakage current from land-line connections (or nearby land-line connections) <electrolytic corrosion>.

 

Thats my question. If they are of use for that scenario then they can stay on.

Edited November 10, 2011 by Evo

[Timleech]

Its another pointless argument...easily resolved.

 

Someone go dangle a magnesium anode in a harbour somewhere. Where your goggles though wont you.

 

 

 

 

Thats my question. If they are of use for that scenario then they can stay on.

 

I don't see it as a pointless argument.

 

I'm fairly sure that Gibbo (right on most things electrical) was adamant that they don't help in that (stray current) situation. You could spend a happy afternoon with the awful search engine trying to find his views . I'm not qualified to comment.

 

Tim

Edited November 10, 2011 by Timleech

[Evo]

I have no problem accepting that from Gibbo. I was leaning towards that thinking anyways. So regardless of what people think themselves and what they are prepared to 'risk'. If you accepted like me that canal water is a dreadful electrolyte rendering Galvanic corrosion meagre to non existant, and accept that Gibbo reckons anodes are no good for stray current electrolytic corrosion. Then why the flying f do we fit them..?

[Albion]

I have no problem accepting that from Gibbo. I was leaning towards that thinking anyways. So regardless of what people think themselves and what they are prepared to 'risk'. If you accepted like me that canal water is a dreadful electrolyte rendering Galvanic corrosion meagre to non existant, and accept that Gibbo reckons anodes are no good for stray current electrolytic corrosion. Then why the flying f do we fit them..?

 

For 'dreaful' read 'poor' and for 'meagre to non existent' read 'slow but observeable' (as most of us would) and you've answered your final question.

Roger

Edited November 10, 2011 by Albion

[Evo]

No, I meant what I said.

[Albion]

No, I meant what I said.

OK then. In that case you will never be convinced. It's your boat and your choice.

Roger

[Nine of Hearts]

Someone go dangle a magnesium anode in a harbour somewhere. Wear your goggles though wont you.

 

Like this, you mean?