Anodes - hull and keel

[Dougie_the_Mate]

We have had problems with rust on the keels of our Centaur since we got her - something that I am always working on . It was suggested to me that by fitting an anode I could prevent this occurring.

We already have a pear shaped anode on the hull and given the level of deterioration it seems to do its job well. Would keel anode(s) be in addition to this and do I need to put one on each keel?

Please excuse me if this seems a rather obvious thing to some here but I am working on the assumption that the only stupid question is the one you don't ask.

Thanks for any advice.

Dougie

 

[sailorman]

We have had problems with rust on the keels of our Centaur since we got her - something that I am always working on . It was suggested to me that by fitting an anode I could prevent this occurring.

We already have a pear shaped anode on the hull and given the level of deterioration it seems to do its job well. Would keel anode(s) be in addition to this and do I need to put one on each keel?

Please excuse me if this seems a rather obvious thing to some here but I am working on the assumption that the only stupid question is the one you don't ask.

Thanks for any advice.

Dougie

rust needs air & water to form the anode will not prevent rust.

 

[VicS]

We have had problems with rust on the keels of our Centaur .......................................

Dougie

rust needs air & water to form the anode will not prevent rust.

So to prevent rusting you need to exclude either water or air

Keel your keels sealed in dry air or immersed only in water which has been boiled to remove air and then sealed with a layer of oil on the surface.

Applying a protective is however the most usual way of protecting cast iron keels. It is essential that all rust and other corrosion products, as well as salt, are removed. Grit blasting is the way to do that. Before a coating is applied it should be confirmed that the surface is salt free by testing with potassium ferricyanide paper.

The first coat ( primer ) should be applied as soon as the surface has been prepared. Before any surface rusting can occur



You dont say what your hull anode is bonded to. Via the engine block to the stern gear? Its unlikely to have been an original fitting, other than as an optional extra , on a Centaur. Whether it is necessary is probably doubtful. The fact that it is corroding away is not an indication that it is actually doing anything useful.

 

[KellysEye]

>The first coat ( primer ) should be applied as soon as the surface has been prepared. Before any surface rusting can occur


The primer, after blasting, should be two coats of zinc rich epoxy.

 

[Dougie_the_Mate]

In the years since I bought the boat - coming up for 10 - I think - I have tried to solve the rust problem by attacking it with an angle grinder and sander before applying two coats of two part epoxy, I had her it blasted (twice) by a firm from the Holy Loch - the first time despite paying for treatment the rust returned before she was even launched the next season - the second I watched while 4 coats of epoxy were applied after blasting. I have also attacked it with an electric chisel and applied coats of Hammerite - which incidentally seems to have been the most effective.

The keels are in quite good nick at the end of the last season, but following the suggestion from my yard neighbour about the keel anodes I thought I would ask here for folks' thoughts.

The pear shaped hull anode was on the boat when we bought her and I have replaced it twice before this winter. I can only assume it was there for a purpose and followed advice about replacement when it deteriorated to a certain point.

 

[sailorman]

In the years since I bought the boat - coming up for 10 - I think - I have tried to solve the rust problem by attacking it with an angle grinder and sander before applying two coats of two part epoxy, I had her it blasted (twice) by a firm from the Holy Loch - the first time despite paying for treatment the rust returned before she was even launched the next season - the second I watched while 4 coats of epoxy were applied after blasting. I have also attacked it with an electric chisel and applied coats of Hammerite - which incidentally seems to have been the most effective.

The keels are in quite good nick at the end of the last season, but following the suggestion from my yard neighbour about the keel anodes I thought I would ask here for folks' thoughts.

The pear shaped hull anode was on the boat when we bought her and I have replaced it twice before this winter. I can only assume it was there for a purpose and followed advice about replacement when it deteriorated to a certain point.

epoxy is never going to work if applied in less than favourable conditions.
i would use international primocon

 

[Dougie_the_Mate]

epoxy is never going to work if applied in less than favourable conditions.
i would use international primocon

I stand corrected - it was international Primocon that the Holy Loch people used and it did not really solve the problem entirely.

 

[sailorman]

I stand corrected - it was international Primocon that the Holy Loch people used and it did not really solve the problem entirely.

Nothing,will ever solve cast iron keels & rust. just keep at it

 

[Tranona]

I stand corrected - it was international Primocon that the Holy Loch people used and it did not really solve the problem entirely.

The basic problem with Centaur keels and many others of that era is that they are poor quality castings and just about impossible to get clean enough for any treatment to stick. You just have to live with it.

It is not galvanic corrosion - that is when there are two dissimilar metals in contact in seawater - but old fashioned rust, so anodes won't make any difference. The anode you have is probably wired through the engine to the shaft and prop and is there to protect the prop as that is often a less noble metal than the shaft it is attached to. 5 years life suggests it is not doing much. The erosion of the zinc is to stop the erosion of zinc in the prop.