Jump to content
Sign in to follow this  
000

Anodes

Recommended Posts

Like 99% of canal boats, mine is steel and presently on the hard awaiting a little underwater maintenance when we return to Holland in April. Before we came home last October I had a quick look around, specifically at the anodes and they are not showing much degradation at all. I am assuming that the anodes will be aluminium, being in fresh water and will have been on the boat for at least four years.

So is there a rule of thumb regarding anode replacement? For example replacing after X amount of decay or X number or years. I'm inclined to just shine them up a bit with the angle grinder and save a few euros, but I don't want to sink the ship for a penny-worth of tar..

Share this post


Link to post
Share on other sites

Fresh water requires Magnesium Anodes, not Aluminium or Zinc. It is not easy to tell the difference between Magnesium and Ally, so if you suspect Ally, they may well be Magnesium already.

Share this post


Link to post
Share on other sites

Zinc (saltwater) rule of thumb was replace when 1/2 used

Thank you, that's what I needed to know. And in that case I will clean the anodes up a bit and get a couple more years out of them.

Fresh water requires Magnesium Anodes, not Aluminium or Zinc. It is not easy to tell the difference between Magnesium and Ally, so if you suspect Ally, they may well be Magnesium already.

What they tell me and do in Europe.. Zinc for seawater, aluminium for dirty skungey freshwater a.k.a the French canals and magnesium for pristine fresh water eg some of the Austrian lakes where you can drink the water.

Share this post


Link to post
Share on other sites

Aluminium can be used on Salt water and in fact, have a few pluses to Zinc. It lasts longer, is not as expensive and does not tend to have deadly impurities. Zinc naturally has Cadnium as an impurity and the removal of cadnium is what makes a Zinc anode "special" over normal everyday Zinc. But you need a larger surface area than Zinc.

Chris, Dirty water is not an issue. "Brakish Water" is as it has a small amount of Salt in it. Ally is good when you are in Brakish water or have to pass between Salt and Fresh. But if the Canal is fresh (doesn't matter how clean as long as it is fresh water), then even Ally will not give you enough protection. Magnesium is the better metal choice.

Share this post


Link to post
Share on other sites

Aluminium can be used on Salt water and in fact, have a few pluses to Zinc. It lasts longer, is not as expensive and does not tend to have deadly impurities. Zinc naturally has Cadnium as an impurity and the removal of cadnium is what makes a Zinc anode "special" over normal everyday Zinc. But you need a larger surface area than Zinc.

 

Chris, Dirty water is not an issue. "Brakish Water" is as it has a small amount of Salt in it. Ally is good when you are in Brakish water or have to pass between Salt and Fresh. But if the Canal is fresh (doesn't matter how clean as long as it is fresh water), then even Ally will not give you enough protection. Magnesium is the better metal choice.

Wheels. what happens to Alloy on a Stainless steel shaft?wouldnt there be a faster reaction,like ss fitting on to a ali mast? found the answer,now this might make good reading.

 

https://www.westmarine.com/WestAdvisor/Preventing-Galvanic-Corrosion

Share this post


Link to post
Share on other sites

I think in my case a middle ground is required.

At the moment the boat is in Hassalt in Holland and the Ijsselmeer is just down the road,and that is open to the sea via a lock. All the rivers of course also end up in the sea and they feed the canal system in Holland and Belgium. So that would be brackish water and aluminium anodes would be the thing. Go further inland (France) and you get into fresher water. And I suspect this is why people on the inland waterways try to cover both eventualities and use aluminium anodes. The only alternative would be to regularly test the water for salinity depending on where you are and change your anodes to suit. Not really practical.

Share this post


Link to post
Share on other sites

Wheels. what happens to Alloy on a Stainless steel shaft?wouldnt there be a faster reaction,like ss fitting on to a ali mast? found the answer,now this might make good reading.

 

 

Great question. Answer is no, no problem. The difference is because these are two different processes, although very closely related. Galvanic corrosion is what takes place between two metals when there is not a conductive circuit (surrounded by water) around them. The exchange of Ions is taking place between the two metals and that produces the corrosion. The sacrificial anode is underwater and is acting as the...errr....Anode. The  Ions are trying to take a different path and just get lost in the water.

The issue of Alluminium and SST reacting is no different for any two Metals. It is all to do with how far apart on the Nobility scale as to how badly they will react. As the scenario we want is to sacrifice a metal, we look for any metal that will be less noble than the one we want to protect.

The Nobility chart gives us Bronze, Steel, Ally, Zinc and then Magnesium in that orderWe want to protect the Steels and Bonzes, so we use the metals below those to sacrifice. Uranium, Cadnium, Arsenic etc are also below Steel, but are not something we want in the environment, so they are not used.

The reason why Magnesium is not used in Salt water is because it is at the bottom of the list and is the most reactive.

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...
Sign in to follow this  

×
×
  • Create New...