might be a silly question,

[MtB]

Why not use wood?

 

 

You're barking up the wrong tree there...

Or perhaps that should be yew are...

Edited February 4, 2017 by Mike the Boilerman

[Peter X]

I expect by now that OP wishes he hadn't asked the question in the first place.

As posts 2 and 3 pretty much answered the OP's question, and later posts suggested some interesting alternative materials, if I were in his shoes I wouldn't feel too miffed. But he'd be wondering where his shoes had gone, and I would have painful feet if he takes a smaller size.

He thought it might be a silly question (it wasn't), so we thought he might like some silly answers thrown in.

[blackrose]

Zinc protects steel (and many other metals) because it is less noble on the galvanic scale, and thus sacrifices itself to protect the steel. It is a protective form of galvanic corrosion, in the same way that aluminium anodes sacrifice themselves to protect the steel hull.

But in the case of Zinga, nobody's ever been able to explain to me why you would want your hull paint to sacrifice itself? Surely you want the protective paint layer to stay put, which is why I'd rather go for a good epoxy. Epoxies are a proven technology and used industrially on commercial projects. As far as I'm aware zinga isn't.

 

 

..,For example I don't think anyone makes engines and prop shafts out of stainless steel, so would there be corrosion where they meet?

 

My Vetus stainless prop shaft must be a rarity then? I thought all prop shafts were stainless?

Edited February 5, 2017 by blackrose

[cuthound]

But in the case of Zinga, nobody's ever been able to explain to me why you would want your hull paint to sacrifice itself? Surely you want the protective paint layer to stay put, which is why I'd rather go for a good epoxy. Epoxies are a proven technology and used industrially on commercial projects. As far as I'm aware zinga isn't.

Zinga is a zinc rich paint (96% zinc when dry), so works in the same way as zinc galvanising. The zinc sacrifices itself to protect the steel, same as your anodes.

 

With regard to commercial applications, there are a couple on the Zinga Web page under case studies.

 

http://www.zinga-uk.com/case-studies

 

My boat was Zinga'd and then epoxied, and when last out of the water at 7 years old, showed zero corrosion, even where the blacking or paint is damaged.

 

Edited to remove a spurious worm.

Edited February 5, 2017 by cuthound

[Murflynn]

 

My Vetus stainless prop shaft must be a rarity then? I thought all prop shafts were stainless?

ah well, it just goes to show how little much you know

[blackrose]

Zinga is a zinc rich paint (96% zinc when dry), so works in the same way as zinc galvanising. The zinc sacrifices itself to protect the steel, same as your anodes.

 

With regard to commercial applications, there last are a couple on the Zinga Web page under case studies.

 

http://www.zinga-uk.com/case-studies

 

My boat was Zinga'd and then epoxied, and when last out of the water at 7 years old, showed zero corrosion.

Well perhaps I'm just being thick, but if the zinc in Zinga paint is sacrificial then surely that means the paint will gradually (or quickly) degrade and disappear? That was my point in my previous post. On the other hand if it doesn't degrade than it's not sacrificial.

 

I use a zinc rich primer (Bonda Primer) for topsides, but it doesn't claim be sacrificial. That's the bit I don't understand about Zinga. I can't help thinking it's a false claim or just muddled thinking.

 

Yours is the first boat I've heard of that's been Zinga'd and epoxied. But why would you paint over Zinga if you want the zinc to be sacrificial? None of this makes any sense to me. You wouldn't paint over your anodes.

 

Also in your case it's difficult to know which system is protecting the steel. I've worked on a Thames passenger boat which was epoxied 10 years earlier with a Sigma epoxy and it was still as good as new.

Edited February 5, 2017 by blackrose

[cuthound]

Well perhaps I'm just being thick, but if the zinc in Zinga paint is sacrificial then surely that means the paint will gradually (or quickly) degrade and disappear? That was my point in my previous post. On the other hand if it doesn't degrade than it's not sacrificial.

I use a zinc rich primer (Bonda Primer) for topsides, but it doesn't claim be sacrificial. That's the bit I don't understand about Zinga. I can't help thinking it's a false claim or just muddled thinking.

Yours is the first boat I've heard of that's been Zinga'd and epoxied. But why would you paint over Zinga if you want the zinc to be sacrificial? None of this makes any sense to me. You wouldn't paint over your anodes.

Also in your case it's difficult to know which system is protecting the steel. I've worked on a Thames passenger boat which was epoxied 10 years earlier with a Sigma epoxy and it was still as good as new.

When the Zinga has sacrificed itself it is time to repaint it. Your Bonda-Primer will work in the same way. If the top surface is scratched, the surrounding zinc will protect the small areas of exposed steel to prevent corrosion. However it will not protect for as long as Zinga due to its lower zinc content.

 

The previous owner specified Zinga under epoxy. The Zinga remains inert until the epoxy is damaged, and then provides protection to the exposed steel until it can be repaired. So far it has not needed reblacking in 10 years.

 

Your example of a boat on the Thames probably has an easier life than one in frequent use on the canals, due to less chance of grounding and fewer locks.

 

My boat is caming out of the water later this year, so I will be able to see if it need reblacking, spot repairs or nothing at all. If it only needs the latter two, then the cost of epoxy over Zinga will have been recovered through not having to have regular docking or reblacking.

 

Edited to unmangle the effects of autowrong .

Edited February 5, 2017 by cuthound

[blackrose]

When the Zinga has sacrificed itself it is time to repaint it. Your Bonda-Primer will work in the same way. If the top surface is scratched, the surrounding zinc will protect the small areas of exposed steel to prevent corrosion. However it will not protect for as long as Zinga due to its lower zinc content.

 

The previous owner specified Zinga under epoxy. The Zinga remains inert until the epoxy is damaged, and then provides protection to the exposed steel until it can be repaired. So far it has not needed reblacking in 10 years.

 

Your example of a boat on the Thames probably has an easier life than one in frequent use on the canals, due to less chance of grounding and fewer locks.

 

My boat is caming out of the water later this year, so I will be able to see if it need reblacking, spot repairs or nothing at all. If it only needs the latter two, then the cost of epoxy over Zinga will have been recovered through not having to have regular docking or reblacking.

 

Edited to unmangle the effects of autowrong .

Ok I understand, apart from the thought that zinc is generally sacrificial in salt water while it's magnesium for fresh water. Also I didn't realise that Zinga was meant to be over-painted and it worked in the way you described. Do most people paint ordinary blacking over Zinga?

 

But your wrong about the epoxied passenger boat I worked on. It was in regular use and saw far more locks than most canal boats. It was also regularly grounded at its mooring.

 

Also, although there are some examples of commercial applications on the Zinga website, unlike epoxy it's not really the industry standard. Any website search will point to hundreds or even thousands of epoxied ships, bridges and underwater structures.

[Tony Brooks]

Do most people paint ordinary blacking over Zinga?

 

 

 

 

I think there is an undesirable reaction between bitumen and zinc so overpainting with a bitumen based blacking may not be such a good idea. Not sure about tar based ones.