How many anodes?

[WotEver]

28 minutes ago, rgreg said:

My John White 57ft has midships recesses built into the hull for central anodes. 

Isn’t the net result of this that they only protect their recess?

[rgreg]

12 minutes ago, WotEver said:

Isn’t the net result of this that they only protect their recess?

Well the hull is in pretty good condition throughout so perhaps they are effective. It seems a lot of work to put into the build for no benefit.

[LEO]

Hi,

It seems you can't win with anodes - I have had front, side and rear anodes fitted to my boat for the last 14 years of ownership (it's a 48ft boat, 20 years old, Tony Francis steelwork) and as a matter of pure interest I had a hull survey carried out 2 years ago. The steelwork was in excellent condition but the Surveyor (Tony Tucker) said there were too many anodes fitted and this can cause problems.......... this line of thinking was confirmed by the Engineer who runs the slipway.......

 

It may be a new idea as in the past people have indicated the more anodes the better.

 

L.

[Alan de Enfield]

9 hours ago, LEO said:

It may be a new idea as in the past people have indicated the more anodes the better.

Not a 'new idea' at all, it is a well known fact, but when I have mentioned it previously I am always 'knocked back' with the 'more is better' mantra.

 

"Cathodic over protection can (almost) be as harmful as under protection. When the anode produces too much current it over protects the more noble metals which cause them to react and produce issues on various boat parts".

 

https://www.anodeoutlet.co.uk/symptoms-of-over-cathodic-protecting/

I would not have thought an anode seller would propose anything that would reduce their income, unless it had some basis of truth behind it.

 

And - similar words here :

http://www.marineprotectionsystems.com.au/mpswp/wp-content/uploads/2011/06/Over-Protection-Explained.pdf

 

And :

 

"Over Protection from Cathodic Protection Systems.

Getting the potential correct with the application of both Impressed Current (ICCP) & Sacrificial anodes to coated Items is essential. Under protection leads to corrosion & metal loss whereas overprotection can lead to coating delamination or blistering due to cathodic disbonding. Different coating systems behave very differently in the presence of cathodic protection, some are totally unsuitable ( such as alkyds & oleo resinous paints) & others such as epoxies & polyurethane behave well as long as they are chosen correctly. Overprotection is particularly associated with ICCP systems".

 

http://www.amteccorrosion.co.uk/cathodic.html

Edited July 28, 2018 by Alan de Enfield

[frangar]

23 hours ago, Machpoint005 said:

It's not so good for wildlife, the environment, or humans exposed to it. Nasty European Commission legislating to protect our safety and health, and that of the natural world. Why can't we be left to poison all and sundry at will?

 

Perhaps a little more thought about priorities is called for? This is the sort of casual anti-EU remark that has contributed to the fiasco we currently find ourselves in.

Well once it’s dry it’s pretty inert...or at least as inert as bitumen...I for one am mourning its passing as I have found it an excellent product for over 20 years...and just maybe we can get it back along with other stuff that Brussels got its knickers in a twist over. 

[blackrose]

On 27/07/2018 at 19:38, Sea Dog said:

Well they're being eaten away nicely, but I can't see what they're protecting as the sides are insulated by blacking and there doesn't seem to be any bare metal in the vicinity.  

I think it's usual practice to paint a hull as well as attaching anodes. Ideally you don't want bare steel in the vicinity!

[blackrose]

On 27/07/2018 at 19:39, WotEver said:

Yup, that confused me too. 

Why are you confused? That picture was taken just after repainting. Isn't that what most people do - paint around their existing anodes? The anodes have been eaten away as a result of not painting for several years. 

[WotEver]

1 minute ago, blackrose said:

Why are you confused? That picture was taken just after repainting. Isn't that what most people do - paint around their existing anodes? The anodes have been eaten away as a result of not painting for several years. 

So prior to the repaint there was lots of bare metal?

[blackrose]

On 27/07/2018 at 19:52, Captain Pegg said:

Or maybe they have been working to protect the hull and the boat has just been blacked. 

Is the correct answer. That's why the boat is in the dry Dock. 

On 27/07/2018 at 19:52, Captain Pegg said:

 It's still only a local effect though. You would need lots of them all over the hull to give full protection.

It's still better protection than most steel canal boats have with just two at the bow and 2 at the stern. 

[blackrose]

On 28/07/2018 at 09:04, Alan de Enfield said:

Not a 'new idea' at all, it is a well known fact, but when I have mentioned it previously I am always 'knocked back' with the 'more is better' mantra.

 

"Cathodic over protection can (almost) be as harmful as under protection. When the anode produces too much current it over protects the more noble metals which cause them to react and produce issues on various boat parts".

 

https://www.anodeoutlet.co.uk/symptoms-of-over-cathodic-protecting/

I would not have thought an anode seller would propose anything that would reduce their income, unless it had some basis of truth behind it.

 

And - similar words here :

http://www.marineprotectionsystems.com.au/mpswp/wp-content/uploads/2011/06/Over-Protection-Explained.pdf

 

And :

 

"Over Protection from Cathodic Protection Systems.

Getting the potential correct with the application of both Impressed Current (ICCP) & Sacrificial anodes to coated Items is essential. Under protection leads to corrosion & metal loss whereas overprotection can lead to coating delamination or blistering due to cathodic disbonding. Different coating systems behave very differently in the presence of cathodic protection, some are totally unsuitable ( such as alkyds & oleo resinous paints) & others such as epoxies & polyurethane behave well as long as they are chosen correctly. Overprotection is particularly associated with ICCP systems".

 

http://www.amteccorrosion.co.uk/cathodic.html

Since they're only meant to work over approx 12ft diameter I think you'd need a lot to over - protect a boat. The bottom of this webpage gives some anode layout plans. I think there's more detail somewhere on the website. 

 

http://mgduff.co.uk/support/fitting-instructions/steel

Edited August 1, 2018 by blackrose

[Sea Dog]

11 hours ago, blackrose said:

I think it's usual practice to paint a hull as well as attaching anodes. Ideally you don't want bare steel in the vicinity!

My point was, if the steel side in the vicinity is protected by blacking and there are no bare metal fittings close by like a prop or skin fittings, etc, what is it that the centre anodes are protecting? 

[David Mack]

On 02/08/2018 at 08:22, Sea Dog said:

My point was, if the steel side in the vicinity is protected by blacking and there are no bare metal fittings close by like a prop or skin fittings, etc, what is it that the centre anodes are protecting? 

The unpainted bottom plate?

[Boater Sam]

I remember being told never to use graphite grease in a stern tube as it is so far up the end of the reactive scale that the brass/bronze/steel around it will be eroded. Yet we can use graphited gland packing.

I have also been told that using graphite grease in automotive wheel bearings can lead to corrosion and early failure for the same reason. The friction and slight magnetism in the wheel and hub causes tiny electric currents to flow.

[Alan de Enfield]

Worth a read if you are unsure about how many anodes to use.

 

https://www.thefitoutpontoon.co.uk/electrics/anodes/

 

 

[Gareth E]

On ‎27‎/‎07‎/‎2018 at 10:16, Machpoint005 said:

It's not so good for wildlife, the environment, or humans exposed to it. Nasty European Commission legislating to protect our safety and health, and that of the natural world. Why can't we be left to poison all and sundry at will?

 

Perhaps a little more thought about priorities is called for? This is the sort of casual anti-EU remark that has contributed to the fiasco we currently find ourselves in.

Could you quote what wildlife deaths are the result of the use of cosmastic paint?

 

This probably isn't the thread for politics but as you started it: The very worst thing a human can do for the environment is to have children. Their future consumption and likely further breeding will, without doubt, cause more damage to the planet than a bit of paint that falls off a narrow boat into the canal. The last time I checked, the EU hadn't banned people having children.

[nb Innisfree]

FWIW when Innisfree (60') was 3  years old and in dry dock I noticed 2 or 3 small pits on starboard and port sides, they were exactly midway between bow and stern anodes. Two years later we dry docked again and fitted extra anodes and since then no pitting occurred. 

[Sea Dog]

8 hours ago, David Mack said:

The unpainted bottom plate?

Nope, that's over the lip of the wearing edge and around a corner. Conventional wisdom on this apparently rather inexact science suggests they only protect within line of sight.

58 minutes ago, nb Innisfree said:

FWIW when Innisfree (60') was 3  years old and in dry dock I noticed 2 or 3 small pits on starboard and port sides, they were exactly midway between bow and stern anodes. Two years later we dry docked again and fitted extra anodes and since then no pitting occurred. 

That's a small sample of course, but possibly the best evidence to date!  Could also be your blacking was more successful though, or the pits were where some mill scale scabbing parted with the plate.

[nb Innisfree]

3 hours ago, Sea Dog said:

That's a small sample of course, but possibly the best evidence to date!  Could also be your blacking was more successful though, or the pits were where some mill scale scabbing parted with the plate.

It was grit blasted soon after initial launch. 

[Sea Dog]

9 hours ago, nb Innisfree said:

It was grit blasted soon after initial launch. 

Well then as I said, it could be the best evidence to date! Did it continue to get worse between year 3 when you noticed it and year 5 when you fitted the anodes?  If it did it might suggest the anodes fixed the issue; if it didn't, some other factor might be involved. 

 

Personally,  I think 3 years to the first re-blacking is too long, although whether that could account for your minor pitting is an unknown.  Subsequent ones may be able to be extended to 3 annual when you have experience of how well the coating is lasting, which might be a function of the steel quality, prep and application, blacking material used, where the boat is kept, earthing arrangements, etc - maybe even the anodes. Just my thoughts though - there are no shortage of conflicting opinions on this subject.

[nb Innisfree]

27 minutes ago, Sea Dog said:

Well then as I said, it could be the best evidence to date! Did it continue to get worse between year 3 when you noticed it and year 5 when you fitted the anodes?  If it did it might suggest the anodes fixed the issue; if it didn't, some other factor might be involved. 

 

Personally,  I think 3 years to the first re-blacking is too long, although whether that could account for your minor pitting is an unknown.  Subsequent ones may be able to be extended to 3 annual when you have experience of how well the coating is lasting, which might be a function of the steel quality, prep and application, blacking material used, where the boat is kept, earthing arrangements, etc - maybe even the anodes. Just my thoughts though - there are no shortage of conflicting opinions on this subject.

The blacking started peeling off a few months after initial launch, most likely not adhering to the mill scale, so we craned out and sandblasted. The pits were noticed about two and a half years later, I think they were slightly worse when we fitted extra anodes two years later but couldn't be certain. As they occurred both sides in exactly the same midpoint it led me to assume they were just beyond the effect of existing anodes. 

[Alan de Enfield]

20 minutes ago, nb Innisfree said:

As they occurred both sides in exactly the same midpoint it led me to assume they were just beyond the effect of existing anodes. 

Interesting - were you continuously cruising, cruising regularly, or a lot of time in a marina ?
Did you turn the boat around and moor 'other side to' sometimes.

 

I'm interested in the 'environmental conditions' that cause pitting - anecdottaly much of it appears to be formed in marinas, and very little on 'cruising boats'

[Captain Pegg]

16 minutes ago, Alan de Enfield said:

Interesting - were you continuously cruising, cruising regularly, or a lot of time in a marina ?
Did you turn the boat around and moor 'other side to' sometimes.

 

I'm interested in the 'environmental conditions' that cause pitting - anecdottaly much of it appears to be formed in marinas, and very little on 'cruising boats'

Most likely candidate is high levels of chloride compounds in the water. The obvious source in a marina being waste water containing cleaning products. It still requires the breakdown of the surface coating to initiate though. It's probably the best reason I can think of to black the baseplate as well as the sides.

 

If you wanted to put some science into it I would start by analysing water samples from a representative sample of differing environments. What I wouldn't be doing is ever mentioning 'quality' of steel; whatever that means.

 

JP

[nb Innisfree]

41 minutes ago, Alan de Enfield said:

Interesting - were you continuously cruising, cruising regularly, or a lot of time in a marina ?
Did you turn the boat around and moor 'other side to' sometimes.

 

I'm interested in the 'environmental conditions' that cause pitting - anecdottaly much of it appears to be formed in marinas, and very little on 'cruising boats'

Shortly after grit blasting we did moor up for 3 months on port side of boat (while we sourced and fitted a new engine) we were on port side and shorepower for that period (quality GI fitted) After that we continuously cruised up and down the country. As pitting was same both sides I discounted this 3 month period of mooring, on inspection they were coloured a bright silver and exactly equidistant between anodes on both sides of boat, too much of a coincidence I thought. 

 

ETA: We were full time retired liveaboards and rarely moored in a marina if we left boat for a few days. 

Edited August 5, 2018 by nb Innisfree

[Chris and PJ]

My opinion as an offshore oil corrosion engineer (retired) is:

 

Sacrificial anodes are used to reduce the potential of a metal to galvanically corrode. Go google `pourbaix diagram mild steel`. (for the hull) Brass for the propeller. Stainless steel for the prop shaft.

Always measure the effectiveness of anodes against a silver/silver chloride half-cell. Go to https://www.galvatest.eu/ to gain an understanding. Too many Sacrificial anodes damage the coatings. Coatings are the primary and most important way to stop hull corrosion. Changing the corrosion potential of the hull correctly promotes and maintains the formation of a natural beneficial passivation film on exposed surfaces.  

Sacrificial anodes correctly implemented will help reduce the more aggressive corrosion caused by stray currents if present. Again stray currents can be detected, identified and traced by use of a half-cell.  

 

See my other post

 

I would always be happy help anyone. Even with the loan of the necessary equipment for those that suspect that something outside their control is corroding their boat.

      

 

 

 

[Boater Sam]

On 27/07/2018 at 15:39, BruceinSanity said:

Dr Bob will be along in a bit to keep us right, but a quick google says it’s a petroleum distillate of well known toxicity:

 

Anyone who’s been near Comastic being applied will know how disgusting it smells.

But I like it. And carbon tetrachloride, methylene chloride, Digoxin, and most things that are bad for me.