At what point do you replace your anodes?

[absit_omen]

And why? One third gone, half gone, two thirds gone?
Disregard other factors such as convenience of changing etc.

Scrooge mode on:

My anodes are approx half gone (after 2 years). There are eight of them at around £40.00 a pop I am reluctant to just bin a sizeable chunk of zinc.

Does it matter if they are 90% gone? They are still sacrifycing and protecting - aren't they?

Scrooge mode off.

 

[Heckler]

my personal view is leave em till they are eaten away to nothing, only caveat, give em a good wire brushing so that fresh zinc is available to be eaten!!
Stu

 

[awol]

From the Volvo website [ QUOTE ]
If an anode for example looks yellow or is covered in white crust it has been pacified and needs to be brushed or changed to provide protection. This can be done by brushing the anodes using sandpaper or an emery cloth. Note, never use a wire brush with steel bristles. You have to use an emery cloth without iron oxide otherwise the anode might be pacified.

[/ QUOTE ]

So no wire brushes !

 

[ghostlymoron]

You could melt the old ones down and make some new ones - this was described in PBO some time ago. I've never tried it though. Presumably, if other owners chuck theirs out when 50% used, there could be plenty of scrap zinc available if you check boatyard skips!

 

[neale]

Normal suggestions are when 50% wasted. I guess the second 50% will go alot quicker than the first 50% due to surface area.

I agree that they will still be working when 90% wasted, but with just 10% left you need to keep a very close eye on them.

If you find yourself with no anodes left, something else more expensive will be eroding.

In reality for most it comes down to changing them when the boat is lifted. The cost of the lift normally makes it uneconomical to try and squeeze an extra few months out of the anodes.

The way I do it is this: the boat is lifted once a year for antifoul and other maintenance. If the anodes are more than 40% wasted at that time, I replace them. Less than 40%, I give em a good clean and leave them another year.

For the sake of a few pounds, it just doesn't seem worth the risk.

 

[Spuddy]

Is that 8 anodes on your Vertue ? My guess is that's more than similar boats - I've heard of it being possible to have anodes eroding but without offering any protective benefit - creating a battery - but I dunno enough about practicals of galvanics. A few owners this way have a big zinc dangling over the side connected to prop shaft etc with croc clips. Obviously needs to be disconnected before chugging off. Could melt your old anodes into a tin can with a coathanger in it as a hook.

 

[kenp]

If your boat is in salt water you should consider aluminium anodes. They are about a third of the price and last longer.

 

[Eeyore]

....also from the internet.......

"The amount of protection a sacrificial anode can give is a matter of its surface area and weight. Factors such as the types of dissimilar metals it’s meant to protect, whether the water is fresh or salty, the water temperature, and the composition of the hull all come into play. Generally speaking, an anode should last a year before it needs replacing. When it’s half gone, that’s the time to install a new one. Zincs that disappear quickly and look shiny, instead of being covered with a layer of zinc oxide, indicate possible trouble with stray current.

Sacrificial anodes needn’t be zinc, though zinc is most common because it’s cheap and one of the least noble metals around. However, in fresh water, zincs develop a coating of zinc hydroxide that insulates it and stops it from supplying those electrons. In other words, it no longer serves as an anode and thus stops sacrificing itself. This can happen in just a couple of months.

Naturally, painting a sacrificial anode will do the same thing. Another good way of stopping the anode from working is to install a new one on a dirty prop shaft. Dirt or paint on the shaft will interrupt the electrical connection. The same goes for anodes mounted on rudders. To work, they’ve got to have a good electrical connection to the metal they’re protecting.

There is an alternative to zinc sacrificial anodes. Performance Metals manufactures sacrificial anodes made from an aluminum-indium alloy that’s less noble than zinc, making it an excellent material to fight galvanic corrosion. According to the company, it has more current capacity for the same volume, which means a given anode made from aluminum alloy will last 50 percent longer than a comparable one made from zinc. It’s also one-and-a-half times lighter than zinc."

 

[absit_omen]

Erm, no. If only I had just my Vertue to worry about! /forums/images/graemlins/smile.gif

This is for my big boat. 46ft steel ketch. /forums/images/graemlins/frown.gif

 

[Billjratt]

If you have 8 anodes, would it be possible to work some kind of rotation?
Do they all get eroded equally?
Maybe change the four worst ones this year (if you normally do it annually) Then, if the old ones totally wear out, you still have protection.
I guess if you don't do it annually you could maybe change two every season. Horses for courses.
When all I had was a shaft anode, I left the old one on and fitted a new one every two years, Nature cleared a place for the incoming anode!

 

[Heckler]

Oh another thought there is an outfit in Belfast that is sellig them on Ebay at about a third of the cost!!
stu

 

[Heckler]

hmm, my view, what a load of bollox, volvo say all sorts of things, put your gearbox in reverse to prevent shaft turning, then advice changes, leave in neutral, hmmm, why? techie I was talking to said they changed their mind, they sometimes jam says he, need a flick with the starter to unlock, punters didnt like that so we changed advice!!!
anyway wtf are anodes to do with volvo in this context? methinks volvo like selling anodes!! expensive anodes!!

 

[VicS]

[ QUOTE ]
anyway wtf are anodes to do with volvo in this context

[/ QUOTE ]The "context" was not initially defined and I think the quotation from Volvo was to counter a suggestion that anodes should be wire brushed. The advice from Volvo on that score is relevant in any context.

The connection with Volvo is in relation to their sail drives, stern dives & outdrives. They also recommend a point at which they should be changed, but I forget what that is. Very important with such aluminium structures immersed in seawater I suggest. Volvo obviously sell anodes as spares for their drives, in the same way as they sell spares for the internal mechanical gibbins, so you would hardly expect them to recommend a "Joe Blogs anode" of unknown specification (normally they are to a US military spec or similar I believe) bought off eBay.

What has no relevance to the discussion on anodes is whether or not to put a gearbox in reverse when sailing!

 

[Heckler]

Vic
you are pretty intelligent BUT sometimes I dispair, point is that all that what volvo says is not gospel and that was the point of my anecdote.
S