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It seems that some current thinking is that Aluminium Anodes are a good compromise for use in Salt, Fresh, and Brackish Water, but then it is also said that there is no 'one suits all' solution, and the following table seems to support this.

Zinc Alloy Anodes = Salt water only

Not recommended for use in fresh water

Aluminum Alloy Anodes = Salt or Brackish water

Not recommended for use in fresh water

Proven to last longer than zinc due to increased capacity

Magnesium Alloy Anodes = Fresh water only

Not recommended for use in salt or brackish water

The only alloy proven to protect your boat in fresh water

From this 'table' it would seem that if you are a 'pure salty', then its Zinc for you, while aluminium will work in both Salt and Brackish.

At what point I wonder, do the Broads become Brackish?

My guess would be Breydon Water, but just how far up the rivers, does the Brackish water extend?

Theoreticallly, if you are equipped for seagoing, then you will have either Zinc or Aluminium anodes, but if you also spend time on the Broads with these types, then you don't have any effective Galvanic protection.

In my case, being Broads based, I should use Magnesium anodes, but if I venture out into the 'Salt', which I could, these won't last very long at all.

What type of anode do you use, and where does your boat spend most of its time?


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When Broads based I had Aluminium on Kiki as a compromise, particularly moored at Goodchilds.

When we moved Kiki to permanent salt it was surprising how they disappeared and were quickly replace by Zinc.

I would thoroughly recommend a Galvanic Isolator for what they cost, much cheaper than new stern gear. :naughty:

Before and after here viewtopic.php?f=37&t=2948&p=137655&hilit=galvanic#p137655


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Aluminium anode is no good for anything with outboard or outdrive as the thing you are trying to protect is aluminium so no difference between the metals.

Not true. The aluminium anodes are a different composition to outdrives and are therefore more reactive than the drive casings. This is why they are able to produce kits specifically for outboards and outdrives http://www.performancemetals.com/anodes/index.shtml

Also in reference to Perry's earlier post, I whole heartedly agree it is worth fitting a galvanic isolator. However, as came out in conversation at the weekend, there does seem to be a misunderstanding how these work. They are only of any use when plugged into shorepower, and will stop your anodes protecting your neighbours boat if there are stray currents or bad earths in the.

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Thanks for you input guys, both interesting and helpful.

The 'link' you posted Mark, does seem to support what my surveyor said, and that is that Aluminium based anodes are the best 'all rounders'.


Navalloy® Aluminum Anodes

The Only Anode That Works in All Types of Water

The aluminum alloy used in Navalloy anodes is very different from normal aluminum. It includes about 5% zinc and a trace of Indium, which prevents the build up of an oxide layer.

Aluminum anode alloy provides more protection and lasts longer than zinc. It will continue to work in freshwater and is safe for use in salt water. Aluminum is the only anode that is safe for all applications.

Navalloy® has a higher protection voltage than zinc.

This particularly important when protecting aluminum components, like an outboard motor, which is an "active" metal.

My guess is that my boat was originally used quite frequently in salt water, as the fact that it has a 'fish finder' (in additional to a depth sounder), a hefty Danforth anchor, and is fitted with the 100HP engine option (for river use only, the Shetland 27 is usually fitted with the 54HP engine), we seem to support this theory.

The anode on my boat is apparently Zinc, and was found to be quite furred over, as a result of being in fresh water.

The boat is coming out of the water next week, for winter period, so plently of time to replace the existing anode. I'll also look into the Galvanic Isolator option too.

My stern gear is a Bronze prop on a stainless steel shaft, and the rudder and its stock are also Bronze. The anode is attached to the end of the drive shaft.


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The anode on my boat is apparently Zinc, and was found to be quite furred over, as a result of being in fresh water.

Yes, that's what happens to zinc in fresh water and the "fur" is impervious to water meaning the anode is doing nothing at all. I found the same thing when we bought Secret Lady. The ones that are ofter overlooked with the engines we have are the heat-exchanger pencil anodes. When I checked these there was nothing left but crumbly chalk :o . I changed those for aluminium too after having the exchangers stripped and flushed.

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