Hull Corrosion

[mutleee]

Hopefully someone can shed some light on my issue.

 

I bought my narrowboat 2 years ago, it's a 2008, when I had it out of the water for a survey the hull was like new, I had it blacked at the time. Now I've just had it pulled out again for blacking and there is lots of corrossion. I moor at a marina and only have a landline connected when I'm there, which is not often as I'm usually out cruising. The boat has a galvanic isolator fitted. Also for the first 5 years of it's life it was a livaboard with the landline permantly connected.

 

I thought galvanic corrosion only happened if you were connected to a landline and didn't have a galvanic isolator. The only changes that have been made to the electric syste is the addition of solar panels with an mppt controller.

 

Does anyone have any idea of what might be causing the accelerated corrosion?

[Leo No2]

The gentleman who used to do my BSS always said it was 12v that was the cause of corrosion which was borne out by a friend who had a horn fitted by a friend of his. The horn used the hull for return and when the boat was docked there was bad pitting corrosion along the vertical lines of the formers inside both front and rear. He moored where there was steel planking along the bankside. The pitting was fixed (puddle welding is a term I remember) and the electrics fixed. That was five years ago and no pitting since.

 

ETA: I don't think there was any need for the power to be on just as long as there was a potential difference between the boat and the steel planking was enough to cause the smallest of currents to start that 'attack'.

Edited September 8, 2015 by Leo No2

[Alan de Enfield]

Is it 'general' corrosion across an area, or, is it localised 'pitting'. ?

 

How do your anodes look ?

 

Have you the correct type of anodes for the type of water you are in ? (Fresh, Brackish, Salt etc)

[alan_fincher]

What do you mean by "a lot of corrosion"? Are there significant pits where there were none before, and, if so do you have any accurate way of measuring them?

 

It is perfectly normal when you pull a boat out to black it to find lots of spots that are "rust coloured", which then expose a shiny surface when pressure washed. However if these are not actually resulting in significant new pits, there are nothing to be concerned about, even if the initial impression you get is not good.

 

I owned our last boat about 10 years, during which it was regularly blacked. Each time it was pulled out I always thought it looked pretty horrible, but in all honesty I had no way of measuring whether it was more pitted or getting worse. I need not have worried - the purchaser's surveyor apparently found it in exceedingly good condition for a 20 year old boat, commenting on it as one of the best he had seen.

I think you need to be clearer about what you are seeing. What causes you to believe it is galvanic?

[Giant]

Have you checked that the galvanic isolator is working correctly? They're quite straightforward to test.

[bigcol]

Worrying to see you boat when first out of the water though!!

Our boat is due out next year, and again when seeing the hull again, I will make me panick.

 

Once cleaned and blacked do feel and boat looks better though.

 

Col

Edited September 8, 2015 by bigcol

[Bee]

Without seeing it it is difficult to hazard a guess but as a rule of thumb I would say that if the paint stays on then you will not get corrosion, if the paint comes off then you will get pitting. Corrosion of steel always seems to take the form of pits and apparently it can have anodes an cathodes within itself that form pits. ( I read that somewhere) The effective area of protection of an anode is not very great and really would not be surprised if they are pointless, and yes I have them as well. I wonder if the last blacking was not too brilliant? I would only use Epoxy, not because it is some sort of magic substance but simply because it stays on. If anybody has a few offcuts of steel it would be really interesting to try a few coatings, hang them in the cut and see what really happens.

[bigcol]

Bee (poster above) testing idea is a good one, Proberly been done before though

I also worry when boat, when first out, there are patches where the paint has worn off, we presure wash and scrape.

We, as in whole family then paint with brush and roller proberly 3 coats over 2 days.

10 litres for a 57 x 10 ft gos on. But is it a good job? Is it protecting the hull?

I would hope so

 

But I really would like to have the hull expoxy or 2 pack but I've always been confused with quotes and costs.

Having the boat sand blasted etc, is 2 pack the same as expoxy etc?

 

I also have a galvanic isolator which is working

 

Col

Edited September 8, 2015 by bigcol

[BenC]

All it takes is Is you or a neighbour to spill a bit of diesel and your blacking can be compromised. Your boat might be protected, but I think I'm right in saying that if adjacent boats have no protection, then this can have an effect on your hull.

[bizzard]

Bee (poster above) testing idea is a good one, Proberly been done before though

I also worry when boat, when first out, there are patches where the paint has worn off, we presure wash and scrape.

We, as in whole family then paint with brush and roller proberly 3 coats over 2 days.

10 litres for a 57 x 10 ft gos on. But is it a good job? Is it protecting the hull?

I would hope so

 

But I really would like to have the hull expoxy or 2 pack but I've always been confused with quotes and costs.

Having the boat sand blasted etc, is 2 pack the same as expoxy etc?

 

I also have a galvanic isolator which is working

 

Col

3 coats over 2 days!!! Bitumen? That should take at least 6 days if the weathers fine and longer if it isn't.

[mutleee]

Thanks for your replies.

 

it is general small spots of corrosion across all the hull, the anodes look like they are working, there's still life in them but I'm going to have new ones fitted. I believe they are magnesium.

 

Yes there are lots of spots that are "rust coloured", which then expose a shiny surface when pressure washed, I was just surprised how bad it looks compared to what it was like two years ago (ie no signs of any corossion). The boatyard that's doing the work was also surprised and asked if I was permanantly attached to a landline.

 

The only thing I could think of was that when it was last blacked it was out and back in in a coue of days and the boat might not have been fully dry before the blacking went on.

[mango]

The gentleman who used to do my BSS always said it was 12v that was the cause of corrosion which was borne out by a friend who had a horn fitted by a friend of his. The horn used the hull for return and when the boat was docked there was bad pitting corrosion along the vertical lines of the formers inside both front and rear. He moored where there was steel planking along the bankside. The pitting was fixed (puddle welding is a term I remember) and the electrics fixed. That was five years ago and no pitting since.

 

ETA: I don't think there was any need for the power to be on just as long as there was a potential difference between the boat and the steel planking was enough to cause the smallest of currents to start that 'attack'.

Why would use of the hull for the negative return for the horn matter? It's not going to be in use for long.

 

My understanding is that severe corrosion is generally due to a small difference in potential between the hull and the Earth on a landline. An isolation transformer or galvanic isolator is the usual recommendation to avoid the problem.

[bizzard]

Thanks for your replies.

 

it is general small spots of corrosion across all the hull, the anodes look like they are working, there's still life in them but I'm going to have new ones fitted. I believe they are magnesium.

 

Yes there are lots of spots that are "rust coloured", which then expose a shiny surface when pressure washed, I was just surprised how bad it looks compared to what it was like two years ago (ie no signs of any corossion). The boatyard that's doing the work was also surprised and asked if I was permanantly attached to a landline.

 

The only thing I could think of was that when it was last blacked it was out and back in in a coue of days and the boat might not have been fully dry before the blacking went on.

A couple of days is ridiculous for bitumen and a waste of money. Even on warm days it'll take at least a day to dry properly, and then at least 12 hours drying time between coats and its wise to leave the last coat to dry properly for 48 hours before re-launching.

Edited September 8, 2015 by bizzard

[bigcol]

A couple of days is ridiculous for bitumen and a waste of money. Even on warm days it'll take at least a day to dry properly, and then at least 12 hours drying time between coats and its wise to leave the last coat to dry properly for 48 hours before re-launching.

This is black jack 2 x 5ltr from the chandlers, the blacking was dry before aplying on the next coat.

I thought that was okay

The boat was craned in 2 days later.

 

 

Col

[Alan de Enfield]

This is black jack 2 x 5ltr from the chandlers, the blacking was dry before aplying on the next coat.

I thought that was okay

The boat was craned in 2 days later.

 

 

Col

 

Had a dry 'skin' maybe would not be 'dry'.

 

Had our NB blacked last year (in the summer, warm and dry) by a reputable yard - it took 7 days in total. I'm sure that if they could have done a good job in two days they would have done so to free up the dry dock and get another boat in and blacked.

They do a 'proper job' which is why they have a 9 month+ waiting list.

[Bloomsberry]

Why would use of the hull for the negative return for the horn matter? It's not going to be in use for long.

 

My understanding is that severe corrosion is generally due to a small difference in potential between the hull and the Earth on a landline. An isolation transformer or galvanic isolator is the usual recommendation to avoid the problem.

 

i agree, if the horn was used regularly I could have understood this but I assume the horn is rarely used so the 0v return is not going to be doing anything for very long periods so is going to have little effect on the hull IMO.

[GreyLady]

k

 

 

i agree, if the horn was used regularly I could have understood this but I assume the horn is rarely used so the 0v return is not going to be doing anything for very long periods so is going to have little effect on the hull IMO.

 

Maybe if the Horn Switch was a one of those Bulkhead/Console Rubber Push Types and the back Nut was not tight enough to be water proof on the back terminals it could cause a shorting out or even a mild positive static charge all over the boats hull for a long period of time pulling in those rusty demon devil's.

 

I feel for the OP at least you caught it in time and can give it a new coat of blacking, maybe you could even get the hull tested for positve charges when its out of the water and in the water on your mooring spot. ?

 

Dont know much about it but from what i read you can be moored next to a demon boat with a postive charge or vice versa negative electrolism wrecking our pride and joy.

 

scary stuff.

 

their are a few links on it on google.

 

try not to worry your boat is young and your aware thats good news

Edited September 8, 2015 by grumpy146

[Traveller]

I thought you were only in potential danger if plugged in and/or moored against a metal key heading? Could be wrong though.

[GreyLady]

I just read this I did not take it all in because I had to wipe my botty in fear of all the corosion causing possibilities.

 

http://www.yachtsurvey.com/corrosion_in_marinas.htm

[Ray T]

I would put forward my observations on electrical action / corrosion but I was told by the veritable expert Dave Clinton that my views were just "waffle" so I won't waste folks time.

Edited September 8, 2015 by Ray T

[GreyLady]

I would put forward my observations on electrical action / corrosion but I was told by the veritable expert Dave Clinton that my views were just "waffle" so I won't wast folks time.

Do tell Ray T

 

pwease ?

[Alan de Enfield]

I would put forward my observations on electrical action / corrosion but I was told by the veritable expert Dave Clinton that my views were just "waffle" so I won't wast folks time.

 

Ah - the "expert"

 

Ex is a 'has been' whilst spurt is a drip under pressure.

 

From his recent posts a good description.

[Ray T]

Do tell Ray T

 

pwease ?

 

http://www.canalworld.net/forums/index.php?showtopic=77644&hl=

[David Mack]

When not in use was your landline physically unplugged or just switched off? Galvanic corrosion is a result of the earth wire being connected between shore earth and the boat hull, so simply switching off does not break the circuit. You must unplug the landline connection.

[blackrose]

When not in use was your landline physically unplugged or just switched off? Galvanic corrosion is a result of the earth wire being connected between shore earth and the boat hull, so simply switching off does not break the circuit. You must unplug the landline connection.

Could be that and/or the last blacking job not being very good. Two days in and out isn't adequate unless it's done every year. Last time I blacked my boat it was out for a week and I got 2 coats of quick drying Primocon underwater primer, 2 coats of rylards rytex and 2 coats of rylards premium on. Plus I went around with a wire wheel on an angle grinder first and took any rust and loose paint off. Most yards won't do the job as well as you'd do it yourself.

 

Mind you, having done all that work I still saw the first signs of rust on the waterline 3 years later but was able to leave it another 2 years.