What anodes? Aluminium or zinc?

[davethedog]

Hello all and about to renew all the anodes on the boat (2 on the hull, 1 on the prop and 2 on the bow thruster).

I think I can only get zinc for the prop, but what about the others, should I go for zinc or aluminium.

Boat will be used in the solent and then off to the med mid next year.

DTD

 

[pvb]

Zinc anodes are usually recommended for salt water; aluminium can be used in either salt or brackish water. I'd use zinc.

 

[Quandary]

I use aluminium because the boat resides in fresh water where zinc quickly becomes passivated, if she spent more time in the sea like most I would use Zinc.

 

[davidmh]

Slight Drift. I keep my boat at the top of Portsmouth harbour and use zinc anodes. I find that they do get a white coat on parts of them. ( passisivation ?) , the water is brackish but how little salt makes it brackish and how do you test it.

David MH

 

[davethedog]

Where do you keep your boat as we are at wicor at the moment.

 

[ctva]

I too have just started to think about this as our local Chandler is now advising that aluminium is their anode of choice for both fresh and salt. Like Quandry, the boat is kept in fresh but sails in salt. I did get a dangly magnesium anode when we moved to the canal 14 years ago but never got around to use it. All I have ever had is a shaft anode that is replaced every 3 years with wear that would not last a 4th. So far absolutely no unwanted corrosion (touching wood).

So, any thoughts on the aluminium as I’m a bit of a “if it ain’t broke...” person.

 

[Paul06]

My boat is in kip marina on the Clyde. I only have one anode, its on the propshaft. I've always used an aluminium anode without any problems.

 

[Topcat47]

I used to keep my boat in Fareham Reach, further upstream than Wicor. It's now inHaslar Creek. Never used anything but Zinc.

 

[vyv_cox]

Aluminium has many benefits over zinc. Article coming up in YM soon.

 

[davethedog]

Why is everything so bloody confusing......

 

[langstonelayabout]

Aluminium has many benefits over zinc. Article coming up in YM soon.

Is this all as a result of the recent adverts by the zinc, aluminium and magnesium anode supplier trying to get 'normal yacht owners*' to use aluminium instead of zinc anodes?

And when mine was parked at Wicor I always used zinc anodes. Supposedly zinc erodes faster than aluminium in brackish water, but my main concern was always how fast the weed grew.

* Never met one yet...

 

[vyv_cox]

Is this all as a result of the recent adverts by the zinc, aluminium and magnesium anode supplier trying to get 'normal yacht owners*' to use aluminium instead of zinc anodes?

And when mine was parked at Wicor I always used zinc anodes. Supposedly zinc erodes faster than aluminium in brackish water, but my main concern was always how fast the weed grew.

* Never met one yet...

As you say, the advantages are being promoted by manufacturers. Like most people I have always used zinc and rarely see aluminium ones but having researched the subject I will be looking them out. No negatives that I have found and lots of positives.

 

[Quandary]

Is this all as a result of the recent adverts by the zinc, aluminium and magnesium anode supplier trying to get 'normal yacht owners*' to use aluminium instead of zinc anodes?

And when mine was parked at Wicor I always used zinc anodes. Supposedly zinc erodes faster than aluminium in brackish water, but my main concern was always how fast the weed grew.

* Never met one yet...

No, it is the opposite, in fresh water zinc anodes do not erode at all, within a few weeks they get a passivated coating which stops them providing protection. I have only started using aluminium recently and they too seem to coat over a bit but much more slowly, before that I used a heavy zinc hanging anode that I cleaned with coarse sandpaper about once a month.
This is all much more of an issue for boats with saildrives with their mix of metals; when I had a conventional shaft with a pair of zinc shaft anodes they seemed to clean themselves, probably because of the rapid rotation. In fresh water, like the canal here, stainless steel and bronze both seem to be sufficiently resistant without protection but we do all our sailing in the sea. Brackish water with more salts may be a more aggressive mix than our only very slightly acidic mountain water and for that I would recommend aluminium. Magnesium is good in fresh as long as you do not to to sea for much more than a fortnight after which it has gone.
With a good folding prop. costing £2k I am willing to try very hard to protect it. Until recently you could not get aluminium anodes for the saildrive leg but these are now available, there is now also a split anode kit for older legs where you do not need to take the prop off, but these are only available in zinc so far.

 

[NormanS]

As the melting point of aluminium is a lot higher than that of zinc, as as I make my own anodes, I'll be sticking with zinc.

 

[Tim Good]

As you say, the advantages are being promoted by manufacturers. Like most people I have always used zinc and rarely see aluminium ones but having researched the subject I will be looking them out. No negatives that I have found and lots of positives.

Vyv…since we all very much appreciate the research and work you do in many area… I’m just dragging this back up again. What did you conclude back in 2019?

 

[oldgit]

Why is everything so bloody confusing......

"Brackish water, sometimes termed brack water, is water occurring in a natural environment that has more salinity than freshwater, but not as much as seawater. "

Just where is the divide for those of us on the borderline
Half of the time boat spent in salty water on the flood tide and brackish on the ebb.
Most cruising in salt but a not insignificant amount spent on inland fresh water .
Some folks on our tidal moorings are trying aluminum but vast majority still using zinc.
10 miles either way to fresh water above the lock or mega salty the mouth of the river.

 

[vyv_cox]

Vyv…since we all very much appreciate the research and work you do in many area… I’m just dragging this back up again. What did you conclude back in 2019?

The YM article is on my website at Anodes
There has been a thread on the subject in recent months in which VicS calculated considerable benefits for aluminium not covered in such detail in my article.

 

[Tim Good]

The YM article is on my website at Anodes
There has been a thread on the subject in recent months in which VicS calculated considerable benefits for aluminium not covered in such detail in my article.

Understood. I’m sold.

 

[VicS]

The YM article is on my website at Anodes
There has been a thread on the subject in recent months in which VicS calculated considerable benefits for aluminium not covered in such detail in my article.

Understood. I’m sold.

The post Vyv refers to is in this thread:- Pear Anodes

 

[Laysula]

Whatever you use, you have to use the same throughout the boat. you can't mix and match.