Keel anode

[slipknot]

I have a beneteau with a cast iron keel (& lead bulb)

It is not connected to an anode and I have read that this is usual for a cast iron keel.

However, my keel does have some corrosion which I think has been caused by a combination of water penetrating the epoxy barrier, brackish water, and no anode.

Is a cast Iron & lead keel be more prone to corrosion than a cast iron only keel?

I am considering fitting an anode. should ths be Zinc or Aluminium, and would a 'hang over the side anode' connected to the keel be sufficient

 

[Tranona]

The anode will not do anything. The corrosion will be good old fashioned rust caused by the water getting at it not galvanic action.

 

[mainsail1]

I agree. My experience is that the usefulness of Anodes is totally over rated except on a prop shaft.

The anode will not do anything. The corrosion will be good old fashioned rust caused by the water getting at it not galvanic action.

 

[VicS]

I have a beneteau with a cast iron keel (& lead bulb)

It is not connected to an anode and I have read that this is usual for a cast iron keel.

However, my keel does have some corrosion which I think has been caused by a combination of water penetrating the epoxy barrier, brackish water, and no anode.

Is a cast Iron & lead keel be more prone to corrosion than a cast iron only keel?

I am considering fitting an anode. should ths be Zinc or Aluminium, and would a 'hang over the side anode' connected to the keel be sufficient

I think it probably is. There is about 0.4 to 0.5 volts between them on the galvanic scale http://www.corrosionsource.com/FreeContent/1/Galvanic+Series

Perhaps the right thing to do is to repair the epoxy but if you want to try an anode an aluminium anode is the preferred choice for brackish water but you will need one either side

 

[vyv_cox]

Based on the PMs between us, yours is a most unusual case. Photographs at the bottom of this page http://coxengineering.sharepoint.com/Pages/Corrosion.aspx. The galvanic reaction is between the iron and graphite that makes up cast iron. I'm not sure that the lead bulb has much influence, I don't think you showed me any photos of the interface, where reaction might be expected to be more severe. Also, the damage is quite localised, which suggests to me that it has been caused by water penetrating a barrier coating.

I think the problem needs to be addressed by two means, firstly a sound, waterproof barrier (as far as is possible) and perhaps by the addition of anodes, as per your question. In the circumstances I would use aluminium, bolted to the iron part of the keel. It could be worth trying a pair of hang over the side anodes, one each side.