Galvanic corrosion

[sailor mcgee]

Galvanic corrosion is something we use in the preservation of ships, its really important, we want to make sure that the ships nails or irom do not corrode. i am a bit out of date with this as i usually just fix a block of zink to the ship or boats i help outwith. what its the reason you dont use a copper sheet on the outside of canal boats?

 

[Chewbacka]

Steel preferentially corrodes to ‘protect’ copper which is why we put Zn or Mg anodes on steel boats.

[sailor mcgee]

why not a sheet of zink then? cost?

 

[Dr Bob]

Some people do spray zinc on the steel but it is very expensive. Zinc anodes are much cheaper. 

[dmr]

A few boatyards do offer zinc coating. One does hot sprayed zinc though this is expensive. Several offer "cold galvanising" which is a posh name for a primer containing a lot of zinc.

 

Galvanic corrosion is not usually a significant issue with canal boats on fresh water unless they are moored in a marina with a permanent mains hookup with earth potential problems.

 

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

[Chewbacka]

3 minutes ago, sailor mcgee said:

why not a sheet of zink then? cost?

 

It’s very difficult to fix sheets to a steel boat. Thin sheets would tear, thick sheets would be incredibly expensive.  Generally steel sheets that are Zn coated are done by a hot dip process.  Boats are a bit big to hot dip a hull.

[sailor mcgee]

or galovonise the hull like galvonised fences... i guess im also asking why you black the hull? is it a mix of beck and kalk? (pitch and chalk?)

Edited December 4, 2018 by sailor mcgee

[Dr Bob]

Copper on seagoing boats is a good idea as it stops marine fouling. No one ever really replaced using organic tin as a component of antifouling paints and copper is going the same way. No one seems too bothered about antifouling paints on canal boats but ours looks like it needs it. I used to get a diver to clean the hull of our racing yacht every month. Our canal boat doesn't need to go that fast!

[ditchcrawler]

Just look at the number of boats well over 30 years old on the canals

[Chewbacka]

1 minute ago, sailor mcgee said:

or galovonise the hull like galvonised fences

Takes a big tank to hot dip a boat.............

[sailor mcgee]

1 minute ago, Chewbacka said:

Takes a big tank to hot dip a boat.............

aye, but would it work when the hull is formed, perhaps a way of stopping internal rot too?

[Tumshie]

Some examples of zinc applications 

 

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

 

https://www.gaelforcemarine.co.uk/en/MG-Duff-Zinga-1kg/m-6498.aspx

[peterboat]

I used Zinga on my boat expensive yes good yes, in the scheme of things though as my boat is my home it was cheap

[Boater Sam]

For corrosion in fresh water, ZINC is not reactive enough, we use Magnesium anodes,

 " Blacking " in the old fashioned way was Chalico, coal tar, cow hair and horse dung mixture, later bitumen.  Nowadays much more sophisticated, epoxy resin compounds.

[dmr]

41 minutes ago, sailor mcgee said:

or galovonise the hull like galvonised fences... i guess im also asking why you black the hull? is it a mix of beck and kalk? (pitch and chalk?)

Increasingly canal boats are protected by an epoxy coating. However, whatever the coating the nature of the canals with tight locks and rubbish on the bottom means that any coating gets scraped in places and will need remedial work every  two or three years.

 

On your previous post, I don't see how zinc on the outside would prevent corrosion from the inside.

 

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

[Chewbacka]

3 minutes ago, dmr said:

Increasingly canal boats are protected by an epoxy coating. However, whatever the coating the nature of the canals with tight locks and rubbish on the bottom means that any coating gets scraped in places and will need remedial work every  two or three years.

 

On your previous post, I don't see how zinc on the outside would prevent corrosion from the inside.

 

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

I assumed she meant total immersion of the hull into a molten zinc tank, ie inside & out.  Need a big hoist to rotate the hull as it’s pulled out, wouldn’t want to leave it full of Zinc.

[DandV]

2 hours ago, sailor mcgee said:

Galvanic corrosion is something we use in the preservation of ships, its really important, we want to make sure that the ships nails or irom do not corrode. i am a bit out of date with this as i usually just fix a block of zink to the ship or boats i help outwith. what its the reason you dont use a copper sheet on the outside of canal boats?

 

Copper sheathing wooden sea going craft was primarily a defence against toredo worm but also provided anti fouling. The copper sheathing though was vulnerable to any contact with rocks and gravel though but was easily repaired by over patching.

[rusty69]

8 hours ago, Dr Bob said:

No one seems too bothered about antifouling paints on canal boats but ours looks like it needs it

I don't bother antifouling our sailing boat anymore. Antifouling paint like a lot of other things seems to have had the "environmental" treatment. Who needs barnacle friendly paint

[Shockabilly]

I find this thread very interesting...our last NB suffered from minor galvanic corrosion at 3 years old despite only rarely ever being hooked up to mains, having anodes, galvanic isolator & being blacked annually, however, it was kept in a marina & I was advised the corrosion had probably been caused by either being moored near a poorly earthed boat or steel pontoon stanchion.

 

We are considering a new build on a Colecraft or Tyler Wilson shell & as & when we take the plunge I intend to go for maximum protection against such corrosion, however, as with all things on the cut everyone has a different view as to the best protection!

 

 

[Bee]

How about a layer of epoxy then a layer of fibreglass matting to give it strength then more epoxy then more glass matting and so on, then take away the steel because its not needed any more. Oops, I seem to have invented GRP

[Alan de Enfield]

11 minutes ago, Bee said:

How about a layer of epoxy then a layer of fibreglass matting to give it strength then more epoxy then more glass matting and so on, then take away the steel because its not needed any more. Oops, I seem to have invented GRP

The Royal Navy doesn't appear to have any problems operating GRP ships at 196ft long x 32ft beam weighing 750 tonnes.

 

Why should a 40 - 50 - 60 foot long x 7 foot GRP tube be a problem (after all sewer pipes are made of plastic these days)

[sailor mcgee]

13 minutes ago, Bee said:

How about a layer of epoxy then a layer of fibreglass matting to give it strength then more epoxy then more glass matting and so on, then take away the steel because its not needed any more. Oops, I seem to have invented GRP

 

Just now, Alan de Enfield said:

The Royal Navy doesn't appear to have any problems operating GRP ships at 196ft long x 32ft beam weighing 750 tonnes.

 

Why should a 40 - 50 - 60 foot long x 7 foot GRP tube be a problem (after all sewer pipes are made of plastic these days)

i doubt there are any mine laying ships on the canals

 

[Alan de Enfield]

Is that a reason not to use GRP on the canals ?

 

My Canal / River boat is GRP

[Tumshie]

33 minutes ago, Shockabilly said:

I find this thread very interesting...our last NB suffered from minor galvanic corrosion at 3 years old despite only rarely ever being hooked up to mains, having anodes, galvanic isolator & being blacked annually, however, it was kept in a marina & I was advised the corrosion had probably been caused by either being moored near a poorly earthed boat or steel pontoon stanchion.

 

We are considering a new build on a Colecraft or Tyler Wilson shell & as & when we take the plunge I intend to go for maximum protection against such corrosion, however, as with all things on the cut everyone has a different view as to the best protection!

Then the search function is your friend, there are loads of threads on here discussing exactly this and other various forms of it. I recommend reading as many different threads as you can but don't get your self stuck in a quagmire of despair over it. 

 

 

[sailor mcgee]

10 minutes ago, Alan de Enfield said:

Is that a reason not to use GRP on the canals ?

 

My Canal / River boat is GRP

ice.

you can use GRP if you so wish to (but, that puts me out of a hobby..) and you MUST MUST MUST remove from the water by 1st of november  if in england - ice will crush grp if thick enough and you guys have had canals freeze over completly.