Coppercoat causing corrosion on through hull fittings

[petem]

I don't want to drift the thread so won't make a technical debate here but, just for anyone stumbling across this, many folk hold the opposite view to the above 2 sentences.

Having two non bonded seacocks where one is showing signs of Verdi Gris and one not, I'd be interested in the science.

I wonder if not having bonded seacocks makes them a better candidate for replacing with composite?

 

[kashurst]

just looked at the leesan seacock kits on the website. looks like a good idea to me.
they are made from glass filled nylon - I think the same stuff that the underwater sensor assemblies are made from. Nylon should last forever in seawater.

 

[kashurst]

Having two non bonded seacocks where one is showing signs of Verdi Gris and one not, I'd be interested in the science.

I wonder if not having bonded seacocks makes them a better candidate for replacing with composite?

verdigris is usually just a chemical reaction with water - the greenish one is possibly weeping a bit or at some point in the past its got wet for a while. If you are worried about it give it a clean up with emery cloth. Check it externally next time the boat is out.

I'm a don't bond skin fittings fan on plastic boats - as long as the skin fitting/valve assembly is all the same material.

 

[petem]

verdigris is usually just a chemical reaction with water - the greenish one is possibly weeping a bit or at some point in the past its got wet for a while. If you are worried about it give it a clean up with emery cloth. Check it externally next time the boat is out.

I'm a don't bond skin fittings fan on plastic boats - as long as the skin fitting/valve assembly is all the same material.

Thanks, I suspect you're right, there's some rust marks in the gel coat below it so it's probably weeped at some point in the past. However, the surveyor recommended that it was replaced as part of routine maintenance so I'll do it in the spring. I also need two new seacocks installing for the A/C that's already been fitted so to me it makes sense to do the whole lot in composite and be done with it for the time that I'm likely to own the boat.

 

[Tranona]

I don't want to drift the thread so won't make a technical debate here but, just for anyone stumbling across this, many folk hold the opposite view to the above 2 sentences.

Maybe, but they are in a minority and the vast majority of new boats with their many seacocks are being built without any bonding. So, are all these builders, designers, engineering people etc responsible for these boats wrong?

 

[MapisM]

Maybe, but they are in a minority and the vast majority of new boats with their many seacocks are being built without any bonding.
So, are all these builders, designers, engineering people etc responsible for these boats wrong?

I don't think it's correct to label the choice of bonding as right and no bonding as wrong (or vv). My understanding is that there are pros and cons behind both choices - which is s the reason why I mentioned different schools of thought, to start with.

Incidentally, I obviously lost the plot with newer boatbuilding techniques, because I wasn't aware that the "vast majority" of new boats are now built with no bonding - are they?
Anyhow, that confirms (sort of) that it isn't a clear cut choice, if you think about it.
I mean, if it would be better in all respects to avoid bonding, why would anyone bother - even if just a small minority?
After all, it's an additional cost for the builder - arguably not much in the big scheme, but still...
In fact, I tend to think that THIS could explain better the majority's choice, rather than any science behind it.

 

[jfm]

I'm a don't bond skin fittings fan on plastic boats - as long as the skin fitting/valve assembly is all the same material.

Me too. Problem is finding a metal seacock that is all one material. Even with top drawer gear you have in contact with the seawater a bronze body and a nickel plated brass ball, electrically connected to each other on the inside of the boat by virtue of the ball shaft. That is a galvanic cell and one of the metals will be nobler than the other, which is the case for bonding.

I don't think it's correct to label the choice of bonding as right and no bonding as wrong (or vv). My understanding is that there are pros and cons behind both choices - which is s the reason why I mentioned different schools of thought, to start with.

Incidentally, I obviously lost the plot with newer boatbuilding techniques, because I wasn't aware that the "vast majority" of new boats are now built with no bonding - are they?
Anyhow, that confirms (sort of) that it isn't a clear cut choice, if you think about it.
I mean, if it would be better in all respects to avoid bonding, why would anyone bother - even if just a small minority?
After all, it's an additional cost for the builder - arguably not much in the big scheme, but still...
In fact, I tend to think that THIS could explain better the majority's choice, rather than any science behind it.

Exactly. I'd be very interested to see evidence for "vast majority" too, but even if there is a majority it cannot be assumed that it isn't influenced by cost cutting. Anyway, as you say, there are pros and cons for bonding and not bonding. It is a pity that the Random Harvest MAIB report has influenced quite a lot of people on this topic, given that it wasn't well written on the topic of galvanic and electrolytic corrosion.

 

[Bandit]

Mapism,
Guidi manufacture in brass, bronze, nickle plated brass, aluminium and stainless steel see https://catalogue.guidisrl.it/en/50-pipe-fittings

A continuity test is essential to see if you are connected with a good circuit otherwise pointless.

 

[MapisM]

Thanks for the link, but when I said that they don't make DZR, I didn't imply that their fittings are bronze only.
Just that mine visually look bronze, and I'm pretty sure to see the difference with anything else - bar DZR, possibly.

I see your point ref continuity, hence my previous question:
is it sufficient to check with a multimeter the resistance between each fitting and anodes?
And how many ohms fractions is acceptable to have (if any), to call the continuity good enough?
I suppose that with the multimeter at its most sensible scale, you might not have a 0.00 reading all the time...

PS: on this last point, any other views are welcome - not that I wouldn't trust Bandit reply alone, but I'd be curious to see if there's any widespread consensus.

 

[jfm]

Thanks for the link, but when I said that they don't make DZR, I didn't imply that their fittings are bronze only.
Just that mine visually look bronze, and I'm pretty sure to see the difference with anything else - bar DZR, possibly.

I see your point ref continuity, hence my previous question:
is it sufficient to check with a multimeter the resistance between each fitting and anodes?
And how many ohms fractions is acceptable to have (if any), to call the continuity good enough?
I suppose that with the multimeter at its most sensible scale, you might not have a 0.00 reading all the time...

PS: on this last point, any other views are welcome - not that I wouldn't trust Bandit reply alone, but I'd be curious to see if there's any widespread consensus.

Mapism, because copper wire is so conductive you're looking for values close to zero. On a plastic multimetre that can't measure milli-ohms well, you want zero on the display. Here is the context: copper wire 6mm sq has resistance at normal boat temps = about 3 ohms/per 1000 metres. 10mm sq copper (which is how mine is built) will obviously be =2 ohms/ thousand metres. Obviously we are talking about cable lengths of just a few metres, so you are looking for zero on a multimeter. If you have a super-accurate multimeter you can work out expected ohm values but readings but you will need to be concerned about bad contacts if you see even 0.01 Ohms on a high spec boat.

 

[MapisM]

Thanks J, makes very good sense.
The multimeter I keep onboard is a pretty cheap thing, but I half recall to have seen a professional Fluke micro-ohmmeter among all the weapons of a friend of mine who is an electronic engineer - I'll borrow it from him for the test! :encouragement:
Incidentally, also the DP bonding cables are pretty thick - by heart I would say the same 10sq mm as yours, if not even more.
I'll re-check that too, anyway I fully agree that in principle, unless there's some corrosion or loose nut somewhere, the resistance should be as close to zero Ohms as it gets.

 

[p435]

I also cannot imagine Coppercoat, which electrically an insulator caused skin fitting to corrode.

I am preparing these days my boat for CC and consider to even to CC my saildrive and propeller. While doing so I take care that the oil change screw and the screw at the end of the spinner of the propeller are not CC.

 

[Portofino]

I know the CC blurb claims CC is electrically inert ( it would claim that ) on the basis the metals coated in resin .
But for the stuff to work - it then contradicts itself by saying it’s the exposed copper ,and furthermore it seems acceptable practice to lightly rub it .
So rubbing off any resin and exposing the metal .

Then compute stern drive s. Accepted practice is to leave a border around the transom flange of say 1 inch / 1 cm ?
This margin of plastic only to stop the “ metals “ in most normal AF s touching the ally flange .

The green colour of the CC ver d Gris is a result of an electrolytic reaction ,
Slapping a layer ,a thick layer of copper under your hull is counter intuitive in terms of some sort of electrolysis somewhere ?
So to me there’s some smoke and mirrors here to CC claim of nil effect in the corrosion of through the hull fittings ? Or any other metal dangling bits in seawater .

Confused

 

[jfm]

The green colour of the CC ver d Gris is a result of an electrolytic reaction

No it's not! It's just oxides/carbonates/chlorides/others resulting from exposure to seawater and damp air

 

[Portofino]

No it's not! It's just oxides/carbonates/chlorides/others resulting from exposure to seawater and damp air

Was thinking ALL chemical reactions involving metals inc ^^^ involve movement of electrons and other particles to create the bonds .Salt solutions help .
It’s just an inadvertent by product corrosion .—- Somewhere that’s the point - where ?

 

[Portofino]

Was thinking ALL chemical reactions involving metals inc ^^^ involve movement of electrons and other particles to create the bonds .Salt solutions help .
It’s just an inadvertent by product corrosion .—- Somewhere that’s the point - where ?

Interesting bit on the Navy —— run it by me again — coating your boat with copper
https://en.m.wikipedia.org/wiki/Galvanic_corrosion

 

[Portofino]

So what you need to know is IF and it’s a big IF — the anodic index of the CC is identical to the various metal bits inc the skin fittings .
If it’s different chances are corrosion will take place .Could be fast ,could be slow .
Just need to know if your zinc s can cope .
This explains MapishM , mates predicament in post #1

 

[kashurst]

as per other threads - copper coat is non conducting. Its just copper dust suspended in epoxy resin. Some of which is exposed at the surface exposing pure copper, copper oxides, copper carbonates etc to sea water which the creepy crawlies don't like.
On its own it cannot create an electrical circuit, nor can it be a cause of galvanic corrosion because it cannot create a galvanic cell. Galvanic corrosion isn't witchcraft it pretty simple chemistry.

Arguably the best thing you could do with your underwater metal fittings is to copper coat them. It acts as an electrical insulator and an antifoul.

Whatever Mapism's friends problem is, removing the last thing you THINK you did to the boat is not a great way of solving a serious problem.

 

[kashurst]

I also cannot imagine Coppercoat, which electrically an insulator caused skin fitting to corrode.

I am preparing these days my boat for CC and consider to even to CC my saildrive and propeller. While doing so I take care that the oil change screw and the screw at the end of the spinner of the propeller are not CC.

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

 

[Portofino]

as per other threads - copper coat is non conducting. Its just copper dust suspended in epoxy resin. Some of which is exposed at the surface exposing pure copper, copper oxides, copper carbonates .

That’s the contradiction
It’s the cuporous oxide actually that keeps the creepy crawly s away
Nether the less if it was totally covered by resin - then yup - inert from an electrolytically pov

You can’t have both logically
Coated in a resin - call it epoxy to seal and hold the copper particles.Creppy crawls attach to the epoxy resin - claim its electrolytically inert to chemical reaction in salt water .Which it would be if fully coated ,but 8hoite as an anti foul

Then in the next breath expose the outer surface copper particles by removing this protective coating to make cupouros oxide , to work as a AF - which involves a chemical reaction which with an anodic metal in a salt solution thats gonna potentially cause corrosion to anther dissimilar anodic metal nearby .

There’s two issues here the epoxy coat to stick and arguably protect the hull - agree - that’s not i,am carping on about btw
AND the AF side of CC
For the AF side to work cuporous oxide has to be generated from exposed copper and regenerated as the stuff wears .

So as stop go electrolytic process / reaction as more exposed neat copper oxidise to form critter hating surface .
Episodes of high activity say after a long high speed blast or scrub and equally episodes of low or zero activity if the boat is parked for a long time .

Dangly bits are skin fitting , rudders , P brackets , shafts , props , outdrives
And Zinc s
Maybe your zincs can,t see the CC skin fittings ?
One assumes because the Zincs have a waaay higher anodic nimbler , they take the hit .
So your big Zinc ( the bigger the worse this effect —- ) take somthing out of the copper coat on the skin fitting cos it’s higher in the anodic table - then the CC as it wears thin on the skin fitting starts to take somthing out of the skin fitting due its difference of anodic potential.

The CC is sandwich between - when it’s thin or if the resin breaks down - insulating it .

All ,am saying coating zillions copper particles on your hull could upset the equilibrium likely if in contact with other metals
Your boggo AF s use copper oxides too but a lot less concentrated, but enough to stay clear of ally sterdives .
With Trilux and such other stern drive - aluminium units the magic ingredient is copper thiocyanate .Halides form strong bonds the copper stays inert electrolytically even in seawater salts - hence the drive does not fizz away under the AF .