Coppercoat causing corrosion on through hull fittings

[Portofino]

my experience of CC on metal bits/props is that it falls off again - better to velox and use whatever
is recommended for the saildrive

Exactly - electrolytic activity on the surface of the “ metal “ , breaking the epoxy bond .
Coursed by neat copper and cuporous oxide .

Trilux and other stuff for drives / sail drives contains copper fixed in an inert ( electrolytic manner )- halide eg cyanide .

 

[kashurst]

the essence of this is that if you put a lump of copper and a lump of zinc in a bucket of sea water and they are not electrically connected to each other or touching each other, the zinc reacts with the chemicals in the sea water, the copper reacts with the chemicals in the sea water. Oxides etc are created and create an insulation like coating. The zinc and the copper do not react with each other.

BUT if the lump of copper and the lump of zinc are electrically connected (either by a wire or physically touching each other) then you have created a simple battery, current will flow in the wire and the zinc errodes.

The exposed copper in copper coat is not in electrical contact with the other metals of the underwater metal work. So no current can flow.

 

[Portofino]

the essence of this is that if you put a lump of copper and a lump of zinc in a bucket of sea water and they are not electrically connected to each other or touching each other, the zinc reacts with the chemicals in the sea water, the copper reacts with the chemicals in the sea water. Oxides etc are created and create an insulation like coating. The zinc and the copper do not react with each other.

BUT if the lump of copper and the lump of zinc are electrically connected (either by a wire or physically touching each other) then you have created a simple battery, current will flow in the wire and the zinc errodes.

The exposed copper in copper coat is not in electrical contact with the other metals of the underwater metal work. So no current can flow.

Corrosive electrolytically activity can take place between skin fittings and CC due to the possible difference of the anodic potentials .The salts in the sea water potentate this locally .

Let’s leave it there , there’s about 30 subatomic particles moving all directions in the creation of a “current “ not just electrons .
We are interested in premature breakdown of some metal skin fittings coverd by CC .

 

[Portofino]

Here an interesting one

Take helium atomic number 2 .
This means in simplistic terms it’s got two neutrons and two protons in the nucleus with two elections orbiting .

School boy level

Then split it to form Hydrogen atomic number one - one neutron one proton in the new nucleus with one electron orbiting .
Two atoms of H for every atom of He split .

Now seperate the new H gas into two containers

Keep one @ CERN ( Geneva )

Send the other to Tokyo .

Bombard the Geneva sample ( remember 1/2 randomly sampled of the H produced by splitting He ) with something to reverse the orbital spin of the one electron .

Spontaneously the electrons in the Toykio sample ( the other 1/2 of the same Orginal He molecules) change rotation and copy
Nobody can explain thus far
So just illustrating there’s a lot more going on , and we don,t know why !

 

[Scarron]

my experience of CC on metal bits/props is that it falls off again - better to velox and use whatever
is recommended for the saildrive

I copper coated my trim tabs and Marelon skin fittings in 2013, the boat has been in the water pretty much continuously since then and has stayed pretty well stuck on.

Before launch

 

[kashurst]

yes it stayed on my trim tabs and rams and all the skin fittings and mostly on the P brackets, but it came off the prop shafts and rudders pretty quickly. I believe Hurricane had similar results. Sorry I have posted this topic before and not given enough detail on this occasion.

However the reason its came off polished stainless steel and polished bronze is not chemical, its mechanical

edit just noticed you copper coated right up to your transom shield - I presume your highly reactive aluminium alloy transom shield is perfectly OK ??

 

[MapisM]

You can’t have both logically

You'll forgive me for not even trying to understand exactly the relationship with CERN experiments , but I must say that in principle the point you are raising makes good sense.
Of course I don't have any scientific answer (either way), but what makes me reasonably comfortable with my idea of joining the CC club is the fact that the issue which I mentioned in my OP seems very far from being widespread.
And even in that case, there's no positive evidence that CC was to blame.
The boat of that chap is still sheltered atm, but I don't dare thinking how pixxed he would be if after stripping CC and replacing several skin fittings he should still have the same issue... :ambivalence:
Time will tell!

 

[MapisM]

However the reason its came off polished stainless steel and polished bronze is not chemical, its mechanical

Yup, I also suspect that the difficulty in this case has more to see with finding a primer that effectively sticks to both metal and CC - and strongly enough to withstand very high water pressure, on top of that.
Easier said that done, I reckon!

 

[Bandit]

Good practice is to leave a gap around a transom shield of 20mm before the CC begins, CC and aluminium do not mix well.

On Scarron's post what are the trim tabs made of ? If aluminium they should be thoroughly cleaned of cc and a 20mm gap.

I certainly would not CC P brackets, shafts and props, Props and P brackets are copper alloy anyway and if you CC or paint and antifoul props you cant pull the shafts without scraping off all of the paint or you destroy the cutless bearings. Where i am in the CI's the best is to acid clean the props & Shaft, wash off well and leave them bare.

 

[Portofino]

Athought occured to me about the colour green ish colour- I,ll come to that last

There’s inconsistency on the CC blurb - that’s all I,am pointing out .

1st - unique water soluble epoxy - to rub off and expose fresh copper
That contradicts with the “ two pack “ osmosis Protection , Does it form a protective coat or is it ( epoxy bit ) soluble ?

2nd the metal — copper re - exposing n the surface to react to create the critter antifouling - inert - can,t be there’s metallic chemistry in there somewhere in a salt solution ,some potential( scuse the pun ) electrons + others movement .

3rd - colour - copper oxide or cuporous oxide the CC blurb claims is in fact RED not green

Here’s a copy from a previous post from a formulate challenging it’s ok to put it on alloy legs / sail drives

Sorry for the advanced chemistry, but the CC blurb is misleading

“”Firstly, no copper compound which forms upon a copper surface is going to be ‘inert’. There will be some solubility, normally giving rise to enhanced copper in local solution (see below).

Secondly, I am not convinced that a copper oxide is the ultimate solid corrosion product on a copper surface immersed in seawater. I answered an old question by macd on this subject, on a recently resuscitated thread here: http://www.ybw.com/forums/showthread...ore-coppercoat.

This was macd’s orginal point:

‘According to Coppercoat's website:
"On immersion sea water attacks the exposed pure copper powder, causing the formation of cuprous oxide. This highly effective antifouling agent deters growth until the surface degrades further to become cupric hydrochloride. This final copper form is highly unstable, and is washed away by the movement of the yacht, thereby removing any accumulating silt or slime. This automatically reveals a fresh copper rich surface, whereby the process recommences."

Yet according to Wiki, cuprous oxide is red, sometimes yellow. So what's the green? (Evidently cuprous chloride (CuCl or Cu2Cl2) is green; cupric chloride, yellowish to brown; couldn't find any references to cupric hydrochloride.)

I've noticed that Coppercoat usually becomes a dull, dirty green, but occasionally have seen it much brighter and paler, almost an emerald green.

Any chemists out there?’

This was my (Hydrozoan’s) response:

‘Reading this resuscitated thread, with which I was not previously familiar, has prompted me to try to address your puzzlement.

Cuprite, the mineral form of cuprous oxide, is indeed red. I am not certain what compound is described by the term ‘cupric hydrochloride’; only a few chemical sites refer to it, but one of them gives the formula ClCuH+2 which surprises me as a positive charge would not apply to a solid compound, but to an ion. It’s odd: perhaps it refers to cupric chloride (CuCl2 (s)), which is green. (BTW, I use (s) to indicate a solid – not absolutely necessary here, but a widespread convention in aquatic chemistry to distinguish solid phases from dissolved complexes having the same formula.)

But as the name and formula are not chemically clear, I won’t pursue that further - especially as several other copper corrosion products are, I think, more likely to be ultimately stable under seawater conditions, and are also green. These are:

A basic copper carbonate: Cu2CO3(OH)2 (s), Malachite in mineral form, which is the typical patina on bronze statuary exposed to weathering (aka verdigris, although that is also applied to a copper acetate).

A basic copper chloride: Cu2Cl(OH)3 (s), Paratacamite in mineral form (also Atacamite, Botallackite and Clinoatacamite).

I have not done a detailed literature search, and many relevant papers would be behind paywalls, but an abstract here http://www.sciencedirect.com/science...10938X04001350 of the paper by L. Núñez et alia, ‘Corrosion of copper in seawater and its aerosols in a tropical island’, Corrosion Science, 47(2), 461-484) reports that Paratacamite was found to be the main copper patina ‘... formed under complete immersion, on the line of water and in the splash zone’.

So, my suspicion is that the green colour is a basic cupric chloride, although a basic copper carbonate (Malachite) might be another possibility (the phase diagram in Figure 4 here http://cool.conservation-us.org/jaic...-03-007_2.html shows the Paratacamite/Malachite boundary occurs at around the typical pH of seawater).

I am sorry that this is rather a late response, but hope you and others may find it interesting and/or helpful nonetheless.’


With regard to the present thread, I emphasize that I wish only to:

1. Correct the notion that any corrosion layer on copper in contact with seawater will be completely ‘inert’. The laws of chemistry and physics mean that, unless the background concentration of dissolved copper is higher than the solubility of the copper corrosion product, there will be an enhanced dissolved copper concentration in the immediate vicinity of a layer of corrosion product on the surface of a copper particle.

2. Point out that the ultimate solid corrosion product is likely IMO to be not cupric oxide but a basic cupric carbonate - a hydroxy carbonate, if you prefer - like Cu2CO3(OH)2 (s) (in mineral form, Malachite) or, and probably more likely, a basic copper chloride - a hydroxy chloride, if you prefer - like Cu2Cl(OH)3 (s) (in mineral form, Paratacamite). (It is also possible that either a basic chloride or a basic carbonate might form, under different conditions.)

Since writing my reply to macd’s original query, it has occurred to me that the Coppercoat site’s ‘cupric hydrochloride’ might in fact mean a ‘copper hydroxy chloride’ like Cu2Cl(OH)3 (s). But this may not be the case, and as the name ‘cupric hydrochloride’ is chemically unclear, I think it would be helpful to use modern chemical nomenclature in discussing what substances are likely to be involved.
Read more at http://www.ybw.com/forums/showthrea...lem-With-Coppercoat/page2#qCCmvK4Ddvotbgdm.99
————————//———————————————-//———————————————-//————————————//————————-

Regarding MapishM point above re - “there’s no positive evidence that CC is to blame “ — for the seemingly seacock damage
It’s too early to tell or peeps arn,t looking .
Just seem odd to say in one breath “ keep x cm margin from transom shield “ then dismiss coating your metal through the hull .
Ok AL has a greater anodic number ( see my wiki link ^^^- post # 36 ) but how do you know CC s anodic number is identical to CC ( in its various evolving forms ) -then these are identical to your metal through the hull fittings ?

As said the thrust of my posts are based on the difference in anodic values of metals , the movement of subatomic particles in chemical reactions with metals in a salt solution acting as an electrolyte.

Which may Lead to degradation of the underwater metal structure s — unknowingly

The inconsistency’s of the CC blurb raises suspicions.

 

[Portofino]

Where i am in the CI's the best is to acid clean the props & Shaft, wash off well and leave them bare.

So they can continue to receive the full and maximum benefit of protection from your Zincs .

 

[Hydrozoan]

...
Here’s a copy from a previous post from a formulate challenging it’s ok to put it on alloy legs / sail drives ...
Read more at http://www.ybw.com/forums/showthrea...lem-With-Coppercoat/page2#qCCmvK4Ddvotbgdm.99
...

As you have quoted me extensively from another thread, I think it only fair to point out that – if your ‘formulate’ is a typographical error for ‘forumite’, as seems likely – I was not ‘... challenging it’s OK to put it on alloy legs / sail drives’.

Rather, I was simply attempting to clarify in precise and specific chemical terms the likely nature of the chemical corrosion products of metallic copper in seawater.

I would only add to what I wrote there that I would also expect cupric oxide (CuO (s), Tenorite, grey/black) to be the more thermodynamically stable oxide in normal seawater in equilibrium with the atmosphere (compared with cuprous oxide Cu2O (s)), but whether or not it will be found in practice when copper metal is exposed to seawater I do not know – I suspect it will be, but it would in any case ultimately convert to the more thermodynamically stable green basic chloride (or possibly the basic carbonate) as I described.

 

[[2068]]

I would only add to what I wrote there that I would also expect cupric oxide (CuO (s), Tenorite, grey/black) to be the more thermodynamically stable oxide in normal seawater in equilibrium with the atmosphere (compared with cuprous oxide Cu2O (s)), but whether or not it will be found in practice when copper metal is exposed to seawater I do not know – I suspect it will be, but it would in any case ultimately convert to the more thermodynamically stable green basic chloride (or possibly the basic carbonate) as I described.

Something just went over my head.
Quite a long way over...

 

[Portofino]

Thx for the clarity Hydrozoan .

 

[jfm]

the essence of this is that if you put a lump of copper and a lump of zinc in a bucket of sea water and they are not electrically connected to each other or touching each other, the zinc reacts with the chemicals in the sea water, the copper reacts with the chemicals in the sea water. Oxides etc are created and create an insulation like coating. The zinc and the copper do not react with each other.

BUT if the lump of copper and the lump of zinc are electrically connected (either by a wire or physically touching each other) then you have created a simple battery, current will flow in the wire and the zinc errodes.

The exposed copper in copper coat is not in electrical contact with the other metals of the underwater metal work. So no current can flow.

Precisely! +1000. So the copper in CC is not part of any galvanic cell/battery.
Now, all you need to do is convince Google-Porto of all that

 

[Hydrozoan]

Something just went over my head.
Quite a long way over...

My apologies. As an aquatic chemist by education, having at one time research interests in heavy metals in both fresh and saline waters, I found myself somewhat puzzled over 10 years ago (when there was a lot of discussion in the magazines and forums of various ‘copper-in-epoxy’ products) by the descriptions of the products of chemical copper corrosion in seawater, and set myself to sorting it out to my own satisfaction.

I do sympathize with those writing for a non-chemical readership – and with those who find my posts on the subject difficult. Unfortunately there is danger of confusion unless likely substances are correctly identified – not so much with the mineral names, which typically refer to naturally-occurring crystalline forms and ores, but with modern chemical nomenclature and formulae. And it is difficult to write with accuracy and concision without using the appropriate chemical terms like ‘thermodynamic equilibrium' or ‘thermodynamic stability’.

Put simply, and as far as I can see, in normal aerated seawater there is evidence of a chemical ‘progression’ from metallic copper, to an oxide (cuprous and/or cupric) to a green basic chloride (or perhaps, especially at lower salinity and therefore lower chloride concentration, to a green basic carbonate like the verdigris we see on copper roofs and bronze statuary).

I talk about the relative thermodynamic stabilities of different solid corrosion products, and thermodynamic equilibrium may take a long time to establish because of slow kinetics. Less thermodynamically stable products may persist alongside those that are more thermodynamically stable, which are the ‘ultimate’ chemical corrosion products over time.

I am not an expert on copper toxicity or antifouling, but do know that in terms of copper in solution (which includes many different dissolved copper complexes, with hydroxyl and chloride ions for example) there is much accumulated evidence that the free cupric ion (Cu2+) concentration is often the best predictor of toxicity to many aquatic organisms. As the ‘earlier’, less thermodynamically stable solids will typically maintain a higher Cu2+ concentration in the boundary seawater, to the extent that antifouling properties are a function of the dissolved copper in the boundary layer they will I presume be at least as effective as the ultimately thermodynamically stable forms.

I’ve perhaps made things worse for you – if so, I'm sorry but I have tried!

Thx for the clarity Hydrozoan .

My pleasure. I just wished to be clear that I was commenting only on the chemistry.

 

[p435]

my experience of CC on metal bits/props is that it falls off again - better to velox and use whatever
is recommended for the saildrive

For the saildrive and props I want to use a primer first. CC is recommended for metal hulls (steel, alluminum, etc).

But, why do you think it will fall of props?
What material is your prop made of?
What primer did you paint and how often before coppercoating your prop?

 

[[2068]]

I’ve perhaps made things worse for you – if so, I'm sorry but I have tried!

Thank you for trying.
It's not your fault that I spent too much time daydreaming in Chemistry lessons.

 

[kashurst]

For the saildrive and props I want to use a primer first. CC is recommended for metal hulls (steel, alluminum, etc).

But, why do you think it will fall of props?
What material is your prop made of?
What primer did you paint and how often before coppercoating your prop?

short answer I don't know why it really comes off, I suspect its lack of mechanical adhesion between the epoxy and the hard metal surfaces combined with water pressure, cavitation and vibration. I don't know what primers were used. My CCoat was done by Costa Blanca Yacht Services in Torrevieja. Dennis has been coppercoating for decades and done loads of boats, including a few forumites here - there is always one or two boats being CCed in the yard.

I have emailed Dennis and ask his experience with saildrives

 

[Scarron]

Good practice is to leave a gap around a transom shield of 20mm before the CC begins, CC and aluminium do not mix well.

On Scarron's post what are the trim tabs made of ? If aluminium they should be thoroughly cleaned of cc and a 20mm gap.

I certainly would not CC P brackets, shafts and props, Props and P brackets are copper alloy anyway and if you CC or paint and antifoul props you cant pull the shafts without scraping off all of the paint or you destroy the cutless bearings. Where i am in the CI's the best is to acid clean the props & Shaft, wash off well and leave them bare.

Trim tabs copper coated
These are as inert/non corrosive as I could make them as the boat lives in the water all year. A bit of a home build project, we CNC milled them from sheet acetal then hinged them with a peek pin and fixed them to the boat with bronze coach bolts, the Lectrotab electric actuators are made from glass filled nylon so the only exposed parts in danger of corroding are a couple of M12 nylon nuts in 316l [let me know if you find a source in bronze?]. I bead blasted them, then painted with a couple of coats of epoxy primer and several of CC. So far they have done pretty well but the lower running surface has eroded and chipped more than on the hull so I do need to re-coat them before they go back in.

Drive shield gap
Because of the conflicting information about CC conductivity I was in two minds about the drive shield but in the end decided not to bother with a margin. I had it and the leg bead blasted and painted with baked epoxy, I then used Hempel Silic One silicone antifoul which has held up pretty well over the 4-5 years it's been in the water. It needs stripping and recoating now though as the silicone on the leading edge of the leg has eroded somewhat. The stainless duo-props are bare and need a good acid clean a couple of times a year. I have just removed the drive shield for inspection, with no signs of corrosion. I am using aluminium anodes which last about 6 months on the Hamble so I am not sure if that is good or bad?