Which anodes Zinc or magnesium

[Ade123]

Hi,
My boat is currently out of water and in need of replacement anodes. However I intend to keep her on the river for approx 6 months then move her round the coast.
Which anodes shall I fit? If I fit mag. for fresh water will they still work in salt or vice-versa if I fit zinc for the sea, will they be effective in the fresh.
Or do I fit both?
What's my best bet?
Any advice would be appreciated?

 

[neale]

Fit Aluminium or fit magnesium now and change to Zinc when you go to salt water.

 

[Chris_d]

Had the same dilemma and fitted aluminium, only about 2 months saltwater use a year and they are now on their 3rd year /forums/images/graemlins/smile.gif

 

[nedmin]

Most Dutch boats use Aluminium. They have a mixture of waters in Holland. I have used Ally for last 20yrs no probs.On steel boats magnesium can be a liability as it can pull the paint off.

 

[John100156]

However outdrives are completely gone..... /forums/images/graemlins/laugh.gif

 

[VicS]

Magnesium is necessary in fresh water because aluminum or zinc will become passivated and will not even recover on retuning to salt water. It is too reactive for use in salt water though.

Aluminium is suitable for brackish water or salt water.

Zinc is only suitable for saltwater

See www.MGDuff.co.uk

Aluminium is as effective as zinc (it is actually an aluminium alloy, containing indium, to a US military specification or similar) it is also cheaper and is said to last up to 25% longer.

 

[hlb]

Stainless steel works for me, they last for ever and look much smarter to. /forums/images/graemlins/grin.gif

 

[VicS]

[ QUOTE ]
Stainless steel works for me, they last for ever

[/ QUOTE ] It'd probably be more accurate to call stainless steel ones cathodes. Bolt a few blocks on to an outdrive leg and you'd probably find out quickly enough which was anodic and which was cathodic. /forums/images/graemlins/shocked.gif

 

[Chris_d]

[ QUOTE ]
However outdrives are completely gone..... /forums/images/graemlins/laugh.gif

[/ QUOTE ]

/forums/images/graemlins/confused.gif err... no their still there, thats 3 years on Volvo DP290 outdrives, as a i said only 2 months saltwater a year, for a boat that does both they work for me.

Actualy their going into their 4th season but on the river any anode lasts a long time.

 

[Elza_Skip]

We are in fresh so use Magnesium, however if going to spend more than a few days in salt water it is best to change.

We spent about a week in saltwater and you could see how the over protection caused the ss trim tabs to go completely shiny. We also saw a significant amount of erosion of the anode in just that week!

 

[DAKA]

Use Zinc.

The zinc is required for salt protection.

In fresh little damage is done anyway.

The zinc gets a coating when used in fresh and needs to be wire brushed off once a month or taken into salt for a few hours to clean and reactivate.

The solution I believe is to use zinc anodes and to drop a lump of magnesium over the side on a wire for use while in fresh water, wrap it round a mooring line so you dont forget to remove it.

The magnesium should keep the zinc clean and ready for salt water use.

 

[VicS]

[ QUOTE ]
Use Zinc ..... The zinc is required for salt protection

[/ QUOTE ] Zinc or aluminium are equally effective in salt water. See my first contribution to this topic) Aluminium is cheaper and is said to last longer. It also remains effective in brackish water.

It is generally advised not to wire brush as you don't want to leave any bits of iron (or rust) embedded in the anode. Clean with coarse glass paper. It is said that the Zn anodes are not reactivated by returning to salt water.

A hanging anode must be positioned close to what it is to protect and it must have a good electrical connection to that item as well. Hanging Zn anodes are available ready made up but I have not seen Mg ones.

Interesting thought that a Mg anode will prevent passivation of the Zn ones!