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Debdale Wharf Molten Zinc Hull Spraying


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33 minutes ago, Alan de Enfield said:

Galvanised gates and construction items are rarely submerged and have loads of 'loose electrical worms floating around them' - Galvanising on gates is not for cathodic protection simply 'rust' protection from casual 'wettings' in the rain.

If they are not submerged they are not galvanised in the normal sense of the term. As for "loose electrical worms" what does that mean?

 

Galvanising isn't "for" cathodic protection, it IS cathodic* protection (against rusting).

 

* - do not write in and tell me it's anodic. It's electrolytic protection in principle.

 

JP

Edited by Captain Pegg
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2 minutes ago, Captain Pegg said:

Galvanising isn't "for" cathodic protection, it IS cathodic protection (against rusting).

 

 

Is it?

 

I thought rust had nothing to do with electrolysis. Am I wrong there? Are there different types of rust? 

 

I too thought galvanising on gates etc might just protect the steel from water and rusting in exactly the same way that paint does, except weather doesn't degrade the zinc coating like it degrades paint (eventually).

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13 minutes ago, Captain Pegg said:

As for "loose electrical worms" what does that mean?

Apologies - I forget that there are newbies to the forum.

A forum term in common use to describe the reason for needing cathodic protection from badly or incorrectly installed electrical systems on land, boat or adjacent boats (commonly called current flow)

 

 

Galvanic Corrosion.gif

 

 

So, in the picture, replace the 'Aluminium Sterndrive' with a Zinc coated Hull and see how long it lasts moored next to the boat with Bronze & Stainless steel hardware.

 

In that instance/example, that is why you need Galvanic Isolators/Transformers

Edited by Alan de Enfield
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6 minutes ago, Alan de Enfield said:

Apologies - I forget that there are newbies to the forum.

A forum term in common use to describe the reason for needing cathodic protection from badly or incorrectly installed electrical systems on land, boat or adjacent boats (commonly called current flow)

 

 

Galvanic Corrosion.gif

 

 

So, in the picture, replace the 'Aluminium Sterndrive' with a Zinc coated Hull and see how long it lasts moored next to the boat with Bronze & Stainless steel hardware.

 

This is why you need Galvanic Isolators/Transformers

 

And IIRC, the 'current flow' is actually the flow of spaces as the electrons shuffling along the wire. The electrons themselves are going the other way which is why the zinc erodes, not the brass and steel. 

 

 

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We're booked in for zinc spraying and 2-pack blacking at Debdale next May - but our boat is 15 years old and we might well own it for another 15 years. The hull is presently in good nick (or was when the boat was surveyed and blacked just over a year ago), so our thinking is that this big up-front spend is worth it to give the hull its best shot at enjoying a healthy middle age - which should help the boat preserve its value and reduce the probability of expensive remedial work being needed in the medium to long term. It also means we'll save the cost and trouble of bitumen blacking every other year; over 15 years, I'd hope no more than one further application of 2-pack would be required.

 

7 x c.£700 for bitumen blacking over 15 years = c.£4900; compared to c.£6000 for one application of molten zinc and two of 2-pack epoxy over the same period. Not that big a difference (although we'll feel like chumps if we end up selling after two years, obviously)!

 

In your shoes, with a nearly-new hull and a shortish period of ownership planned, I think I'd be going for 2-pack alone. I can't see how zinc spraying would come close to paying for itself over that period, either in terms of saving on maintenance or enhancing resale value; whereas I can see how 2-pack might, on both fronts.

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35 minutes ago, Mike the Boilerman said:

 

Is it?

 

I thought rust had nothing to do with electrolysis. Am I wrong there? Are there different types of rust? 

 

I too thought galvanising on gates etc might just protect the steel from water and rusting in exactly the same way that paint does, except weather doesn't degrade the zinc coating like it degrades paint (eventually).

Yes. It's just a protective layer to prevent the parent metal from corroding as it would if it was open to the environment. The galvanic bit only comes into play when the coating is damaged as it continues to protect across minor breaks in the coating in a way that a conventional paint based protective system can't do. Additionally hot dip galvanising offers better protection than hot sprayed zinc or cold applied zinc rich paint in such scenarios.

 

You seem to labouring under the idea that because it is galvanic then it is somehow only applied to prevent galvanic corrosion.

 

JP

 

 

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10 minutes ago, Alan de Enfield said:

This leads me to further confusion -

 

If '2-pack' is so good, why do you need to Zinc-coat underneath it ?

If Zinc-coat is so good, why do you need to '2-pack' over it ?

I think Debdale do suggest that the two pack (or bitumen) is only really required for cosmetic reasons as most people would prefer a black hull to a zinc grey hull.

 

I suggest that any coating will get scrapes and so the epoxy can be repaired, or another coat put on, but a good repair would be much more difficult to a bare zinc hull.

 

..............Dave

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4 minutes ago, Captain Pegg said:

Yes. It's just a protective layer to prevent the parent metal from corroding as it would if it was open to the environment. The galvanic bit only comes into play when the coating is damaged as it continues to protect across minor breaks in the coating in a way that a conventional paint based protective system can't do. Additionally hot dip galvanising offers better protection than hot sprayed zinc or cold applied zinc rich paint in such scenarios.

 

You seem to labouring under the idea that because it is galvanic then it is somehow only applied to prevent galvanic corrosion.

 

JP

 

 

So do you know that hot sprayed metal zinc is inferior to hot dip galvanising?,   and where does sprayed zinc stand on the scheme of things, is it slightly inferior to Hot dipping, or is it little better than Zinga or other paints.

 

I don't fully understand the galvanic thing.  Zinc will protect against galvanic corrosion, but if the zinc gets a scrape to expose the bare steel then do we not have bog standard rusting?? and does Zinc actually help here?   I assume it must because zinc primers appear to work well.  How does the zinc actually stop the oxidation of the exposed bare steel?

 

Is it mostly just that zinc is a good hard well stuck on coating?

 

.................Dave

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15 minutes ago, dmr said:

I think Debdale do suggest that the two pack (or bitumen) is only really required for cosmetic reasons as most people would prefer a black hull to a zinc grey hull.

 

I suggest that any coating will get scrapes and so the epoxy can be repaired, or another coat put on, but a good repair would be much more difficult to a bare zinc hull.

 

..............Dave

Thank you.

 

I have no experience of 2-pack paints, but was under the impression that 'patching / touching up' of 2-pack paint was not an easy job.

 

When I have had to cut down and re-weld galvanised gates to fit a smaller 'gateway' the welds and the Zinc can easily be touched up with a 'rattle-can' of 'liquid zinc'.

 

https://www.e-hardware.co.uk/6504000-p-sitemate-cold-galv-aerosol.html?gclid=CjwKCAiAjNjgBRAgEiwAGLlf2kNx6tz2kTzC_CEzQxnZK9o2lVfxBQht4nUr6MJiKekC_TsfzjyLfBoCdg0QAvD_BwE

 

Cheap Zinc-Paint is available from the likes of Tool Station (£5 can) but it is not the same as the "Cold Galvanising" in the above link.

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1 hour ago, Alan de Enfield said:

Apologies - I forget that there are newbies to the forum.

A forum term in common use to describe the reason for needing cathodic protection from badly or incorrectly installed electrical systems on land, boat or adjacent boats (commonly called current flow)

 

 

Galvanic Corrosion.gif

 

 

So, in the picture, replace the 'Aluminium Sterndrive' with a Zinc coated Hull and see how long it lasts moored next to the boat with Bronze & Stainless steel hardware.

 

In that instance/example, that is why you need Galvanic Isolators/Transformers

The subject is the coating of hulls and the specific analogy you used was the galvanising of garden furniture. All metals have a degree of "floating electrical worms" assuming what you are actually talking about is free electrons. That why they have galvanic properties that vary according to the number of free electrons. So anything that is galvanised has free electrons in its coating. That isn't a problem; it's the intention.

 

The stuff above is about protecting dissimilar metals which obviously involves the use of sacrificial anodes. The complete coating of hulls - or any metal object - with zinc based products is done for a different purpose.

 

JP

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5 minutes ago, Captain Pegg said:

The stuff above is about protecting dissimilar metals which obviously involves the use of sacrificial anodes. The complete coating of hulls - or any metal object - with zinc based products is done for a different purpose.

I realise that it is claimed to be done for a different purpose,(what purpose is it really done for ?) but in reality the coating will erode whether you like it or not - your whole hull becomes an anode. - Unless you cover up the Zinc coating with something else - in which case why Zinc-It  anyway ?

 

I'm sorry, but you are not helping me 'see' the advantages.

 

As far as I am aware the main problem with boat hulls is not corrosion by rusting but corrosion by 'dissimilar metals' causing pitting etc.

Edited by Alan de Enfield
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42 minutes ago, dmr said:

So do you know that hot sprayed metal zinc is inferior to hot dip galvanising?,   and where does sprayed zinc stand on the scheme of things, is it slightly inferior to Hot dipping, or is it little better than Zinga or other paints.

 

I don't fully understand the galvanic thing.  Zinc will protect against galvanic corrosion, but if the zinc gets a scrape to expose the bare steel then do we not have bog standard rusting?? and does Zinc actually help here?   I assume it must because zinc primers appear to work well.  How does the zinc actually stop the oxidation of the exposed bare steel?

 

Is it mostly just that zinc is a good hard well stuck on coating?

 

.................Dave

Hot dip galvanising should provide a better bond and have better galvanic properties than any other available zinc coating. However that's a moot point because you can't hot dip galvanise a boat.

 

Any barrier between two dissimilar metals will prevent galvanic corrosion. That's simply done by forming a water tight barrier so in essence 2 pack epoxy and bitumen protect in exactly the same way as hot dip galvanising or molten zinc spray. They just lose that protection when damaged but zinc based products retain a degree of protection. Where the balance lies I don't know. It would take testing over time to establish that.

 

As for over coating the zinc spray with 2 pack I can't help but wonder if the 2 pack would perform better if it were directly bonded to the hull.

 

JP

 

 

Edited by Captain Pegg
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12 minutes ago, Alan de Enfield said:

I realise that it is claimed to be done for a different purpose,(what purpose is it really done for ?) but in reality the coating will erode whether you like it or not - your whole hull becomes an anode. - Unless you cover up the Zinc coating with something else - in which case why Zinc-It  anyway ?

 

I'm sorry, but you are not helping me 'see' the advantages.

 

As far as I am aware the main problem with boat hulls is not corrosion by rusting but corrosion by 'dissimilar metals' causing pitting etc.

I'm not trying to help you see the advantages; I haven't advocated any form of zinc coating. My point is that crap evidence and misunderstanding of the science isn't helpful to anyone trying to make a decision.

 

I agree pitting is a greater threat although in most cases likely to be a result of specific chemical attack than dissimilar metals.

 

JP

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1 minute ago, Captain Pegg said:

I'm not trying to help you see the advantages;

I think you have pretty much answered the question in your response to Dave.

 

7 minutes ago, Captain Pegg said:

Any barrier between two dissimilar metals will prevent galvanic corrosion.

 

7 minutes ago, Captain Pegg said:

As for over coating the zinc spray with 2 pack I can't help but wonder of the 2 pack would perform better if it were directly bonded to the hull.

 

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18 minutes ago, Alan de Enfield said:

 your whole hull becomes an anode

This is exactly the claim Debdale make for zinc spraying. And yes, as has been said, they claim that a zinc-sprayed hull therefore doesn't strictly need any form of blacking over it. I suppose the idea of the 'belt-and-braces' approach (zinc spraying plus 2-pack) is that you end up with (1) a black hull that should look good for a good long while, and (2) the knowledge that if and when the 2-pack coating gets worn away, the affected areas of the hull won't simply be left with exposed steel, but will have anodic protection provided by the zinc coating.

Edited by magictime
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May I throw a different thought into the discussion. I have always understood that you can use galvanised fuel tanks for petrol but if used for diesel the diesel attacks the zinc in some way. I do know that when we converted a broads cruiser from petrol to diesel we also had to renew the diesel tank because the petrol one was galvanised. Now, if I am right about this will any ordinary bitumen coating do the same? I am NOT talking about two pack, just ordinary or enhanced bitumen over zinc.

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10 minutes ago, Tony Brooks said:

May I throw a different thought into the discussion. I have always understood that you can use galvanised fuel tanks for petrol but if used for diesel the diesel attacks the zinc in some way. I do know that when we converted a broads cruiser from petrol to diesel we also had to renew the diesel tank because the petrol one was galvanised. Now, if I am right about this will any ordinary bitumen coating do the same? I am NOT talking about two pack, just ordinary or enhanced bitumen over zinc.

Similarly - central heating oil (kerosene) delivery will not be dispensed into a galvanised tank. (Not a problem these days with rotational moulded plastic bunded tanks).

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Debdale zinc sprayed our 1988 boat just over 5 years ago, the first boat they did with their new equipment, then applied 2 pack.  We had an out of water hull survey done 2 years ago where the surveyor was very happy with the result 3 years on from spraying, all existing corrosion had been arrested and the zinc showed no sign of wear or de-laminating. (hammer tested) We had been considering another coat of 2 pack as we were 3 years on from what Debdale had done, but the surveyor said don't bother. May have another look next year sometime, but in the meantime we're very happy, and our hull should last a lot longer because of its treatment by Debdale.

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9 hours ago, Alan de Enfield said:

I am yet to be convinced as to the usefulness of Zinc coating as a rust-protector on boat hulls.

 

My thinking :

 

Zinc is used as an Anode on salt-water boats as it erodes whilst giving Cathodic protection. Whilst we normally use Magnesium anodes on Fresh-Water boats, Zinc will still 'perform' the anodic function but at a slower rate than Magnesium.

 

So, why cover you boat in something that is going to erode, when what you actually want is for it to give maximum coverage for rust prevention ?

 

Alternative views and explanations welcomed.

Mine is zingered, then zinger blacked and then I have keelblacked it twice since! The hull is like new, any underwater damage that occours stays just there, nothing spreads underneath it the zinc stops rust dead. I am convinced that it works

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Our boat - a 1999 reeves, is zinc and 2 packed. This was after a survey in 2015 where some pitting was discovered. The pits were puddle welded and then the zinc/2 pack was applied. We have recently purchased an isolation transformer. 

 

As your hull is in good condition, an IT may be a better investment - assuming you are connected to a power supply, and you can take it with you to your next boat. 

 

 

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8 hours ago, dmr said:

 

Surely hot dip and hot spraying do give some chemical bonding, or at least a local alloy, whilst electroplating is just very good painting, and Zinga and Galvafroid etc are just ordinary painting?.   There are a couple of good technical articles on the www, that suggest the alloy at the zinc-steel interface after hot dip galvanising is harder then the steel itself.

 

I am quite tempted by the hot spraying, especially as the boat is approaching middle age, but its a bit costly. I know a lot will get scraped off but what remains should provide some protection. I have seen some hot dip galvanising where the zinc comes off in sheets leaving trapped water behind it, but that's probably not an issue underwater, and should not happen if done well?

 

..................Dave

Zinga is 90 odd percent zinc and sticks like s**t to a blanket! I did a bit of steel at the same time, and it lives in the cut on a bit of wire, no other protection next to steel pilings and still no rust. When it goes rusty I will worry about my boat but until then no worries

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2 hours ago, IDS said:

Debdale zinc sprayed our 1988 boat just over 5 years ago, the first boat they did with their new equipment, then applied 2 pack.  We had an out of water hull survey done 2 years ago where the surveyor was very happy with the result 3 years on from spraying, all existing corrosion had been arrested and the zinc showed no sign of wear or de-laminating. (hammer tested) We had been considering another coat of 2 pack as we were 3 years on from what Debdale had done, but the surveyor said don't bother. May have another look next year sometime, but in the meantime we're very happy, and our hull should last a lot longer because of its treatment by Debdale.

 

Did you do the baseplate too, or just the sides?

 

If just the sides, why are you not worried about the baseplate?

 

Thanks for any comments you have time to add.

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55 minutes ago, Mike the Boilerman said:

 

Did you do the baseplate too, or just the sides?

 

If just the sides, why are you not worried about the baseplate?

 

Thanks for any comments you have time to add.

I can't speak for IDS but I know Debdale include the baseplate as standard.

 

http://www.debdalewharf.co.uk/zinc-metal-spraying/

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