Galvanic Corrosion?

[GUMPY]

If you have anodes and never plug your boat in you should be OK.

As soon as that ground wire is connected your boat starts to go.

It also depends on the water I saw a 5 year old boat from the Rochdale that had only occasionally been connected it had severe pitting.........

[Traveller]

Thanks, so if I plug in occasionally one of hose in-line jobbies should suffice?

[GUMPY]

Thanks, so if I plug in occasionally one of hose in-line jobbies should suffice?

what's an in-line jobbie?

[by'eck]

Is there any factual evidence that a boat sitting on a hook up for 5 years for example without galvnic protection beyond anodes will be affected?

I have heard so many contradicting stories I am starting to wonder what the facts are.

 

I fitted a large 6Kg zinc sacrificial anode to a GRP sailing yacht I owned, electrically linked internally to all the external metal fittings. This was just prior to laying up for winter in a marina in Plymouth. Just outside the marina, bow onto us was a fisheries patrol vessel plugged into its own shore power supply but almost certainly on the same cable run. This was before galvanic isolators became popular.

 

We had to have the boat lifted briefly for a maintenance issue little more than four months later and were surprised to find 70% of the anode erroded away. As intended thankfully it was the less noble metal of the anode that erroded rather than the bronze of the prop or through hull fittings. The similar anode I replaced it with lasted five years but obviously not mooring in the same location.

 

This is a real issue when plugged into a shore power with common earth and adjacent to other boats, especially as there is a much greater surface area of metal underwater with a steel boat. Best be safe but note that in fresh water magnesium anodes are needed.

[John V]

 

I fitted a large 6Kg zinc sacrificial anode to a GRP sailing yacht I owned, electrically linked internally to all the external metal fittings. This was just prior to laying up for winter in a marina in Plymouth. Just outside the marina, bow onto us was a fisheries patrol vessel plugged into its own shore power supply but almost certainly on the same cable run. This was before galvanic isolators became popular.

 

We had to have the boat lifted briefly for a maintenance issue little more than four months later and were surprised to find 70% of the anode erroded away. As intended thankfully it was the less noble metal of the anode that erroded rather than the bronze of the prop or through hull fittings. The similar anode I replaced it with lasted five years but obviously not mooring in the same location.

 

This is a real issue when plugged into a shore power with common earth and adjacent to other boats, especially as there is a much greater surface area of metal underwater with a steel boat. Best be safe but note that in fresh water magnesium anodes are needed.

 

 

Told you....garlic on the fuseboard.....(reply 15)

[Paul's Nulife4-2]

 

 

Told you....garlic on the fuseboard.....(reply 15)

Or post 20,& think about it !

[John V]

Or post 20,& think about it !

 

I bow to your superior botanical knowledge

[Traveller]

what's an in-line jobbie?

One of those galvanic isolators that sits between the boat and the on-shore mains feed - one end of the isolator plugs into the boat and the other end into the shore line.

 

Incidentally, is there a galvanic corrosion issue when plugged into a generator?

[by'eck]

One of those galvanic isolators that sits between the boat and the on-shore mains feed - one end of the isolator plugs into the boat and the other end into the shore line.

 

Incidentally, is there a galvanic corrosion issue when plugged into a generator?

 

Not unless an adjacent boat is plugged into the same generator which in turn is earthed to ground.

[KJT]

Does the condition, thickness and/or type of blacking (ie bitumen or two pack epoxy) have any bearing on the severity of corrosion? Would these 'stray currents' still cause damage or will the blacking provide at least a degree of protection?

I am guessing that it wouldn't help that much, but then again anodes shouldn't be painted for the same reason?

 

Ken

[peterboat]

I am begining to feel a little smug solar panels inverter wispergen 12v dc and no shoreline I knew it made sense

 

Peter

[PhilR]

Is there any factual evidence that a boat sitting on a hook up for 5 years for example without galvnic protection beyond anodes will be affected?

I have heard so many contradicting stories I am starting to wonder what the facts are.

 

5 years on hook-up (and presumably 5 years not boating) is 5 years wasted?

Edited April 12, 2014 by PhilR

[Phil Ambrose]

I am begining to feel a little smug solar panels inverter wispergen 12v dc and no shoreline I knew it made sense

 

Peter

Don't get too smug, galvanic corrosion can still occure with stray DC current.

Phil

[Paul's Nulife4-2]

I am begining to feel a little smug solar panels inverter wispergen 12v dc and no shoreline I knew it made sense

 

Peter

Snap,Snap,Snap,Snap,Snap,Snap and Phil is right so Bugger !

[mark99]

Does the condition, thickness and/or type of blacking (ie bitumen or two pack epoxy) have any bearing on the severity of corrosion? Would these 'stray currents' still cause damage or will the blacking provide at least a degree of protection?

I am guessing that it wouldn't help that much, but then again anodes shouldn't be painted for the same reason?

 

Ken

 

 

Yes - the coating is a form of electrical insulation between the steel and the electrolyte (water). You are taking the electrical continuity out of the galvanic cell and breaking the cell so transport/deposition of metal in the cell (from anode to cathode) cannot take place. Perfect coating = perfect protection. In the real world though, perfect protection is just not and never will be achievable.

 

Not only that, if you had say, just one small hole in the coating you could get a galvanic action in a small area i.e. a concentracted metal degradation/loss in that area and have a pinhole formed - eg say you lose by galavanic action, 25 grams of metal over a year; you could have that loss in a ten pence piece size or (the concentrated pinhole scenario), or spread over the whole hull (no coating).

 

The principle is understood but there are so many variables as there can be local cells formed between your anodes and your hull, parts of your steel and other parts of your steel if your steel varies in composition eg work hardening, parts of your rudder gear etc and your steel, your steel and next doors steel, stray currents, faulty wiring/earthing, your hull and the adjacent piling. (The metals have to form a circuit somehow i.e be connected such as being connected together or touching).

 

The worst sort by far, is when you have external electricity turbo charging the moving/transport of metal ions, so the natual drift of metal between anode and cathode present due to the potential millivolt difference (always present due to the noble difference of dissimilar metals when thos metals touch in the presence of an electrolyte) is accelerated by an external electrical charge which speeds up the reaction.

Edited April 12, 2014 by mark99

[jelunga]

There must be a method so that when other peoples boats in the marina disolve, mine gets electro plated. Maybe if the marina was filled with a copper sulphate solution I could get a copper bottom!

[KJT]

Thanks for the explanation Mark. Very interesting.

[Traveller]

A very interesting and helpful thread. Thanks to all.

[Paul's Nulife4-2]

There must be a method so that when other peoples boats in the marina disolve, mine gets electro plated. Maybe if the marina was filled with a copper sulphate solution I could get a copper bottom!

Trouble is with that idea is, in some Marinas the end result is you would have a hull thickness of several Feet !.

A very interesting and helpful thread. Thanks to all.

Right, now you seam to have a grasp of the basics,,,Can you explain it to me,cos I still ant got it !

 

(Only fooling)

[MunkeyBoy]

Thanks for all the answers very interesting stuff!

The reason I ask as I am looking at buying another boat that has been a floating caravan for years on hook up so I am a bit cautious although I can see the front anodes in perfect nick and the prop feels nice and smooth.

I might pull it into a dry dock and have a closer look.

thanks.

[ditchcrawler]

Thanks for all the answers very interesting stuff!

The reason I ask as I am looking at buying another boat that has been a floating caravan for years on hook up so I am a bit cautious although I can see the front anodes in perfect nick and the prop feels nice and smooth.

I might pull it into a dry dock and have a closer look.

thanks.

I would

[alan_fincher]

Although, That boat look suspiciously like a Sea Otter to me Possibley Marine Grade Aluminum,

 

Is it ?.

 

 

 

I've never seen aluminium go rusty like that...!

 

MtB

 

I think it is also unusual for a Sea Otter to have been overplated!

[Iain_S]

There must be a method so that when other peoples boats in the marina disolve, mine gets electro plated. Maybe if the marina was filled with a copper sulphate solution I could get a copper bottom!

 

There is : an impressed current system, as commonly fitted to slightly larger ships. Not allowed to use it while in port, though, in case chiefy turns it up to steal a bit of plating from the neighbours !

 

Iain

[Paul's Nulife4-2]

-

 

Edited April 12, 2014 by Paul's Nulife4-2

[MunkeyBoy]

So would a 12v only boat not hooked up to shorepower be subject to galvnic corrosion in any way at all?