Anodes in Cardiff Bay and Swansea

Tim O

Tim O

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Hi.....any advice on anodes for the following situation.

Just buying Colvic Countess 33 bilge keel, has been in seawater at Porthcawl last few years and currently has zinc hull anode about 30-40% depleted. Survey picked up minor pinking on prop.....there is currently no shaft anode

She's now on the hard at Cardiff bay where I plan to keep her at least until October then either move to Swansea marina or stay in Cardiff. Both are freshwater I believe with maybe occasional salt input at Swansea???? Shell be on the mooring probably 95% of the time for next year or two i would guess

What would people recommend?....my research suggests replacing zinc with magnesium on hull and adding a collar/ball anode on prop shaft?

I'm an anode newbie never had anything to do with em before!!!
 
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Tim O said:
Hi.....any advice on anodes for the following situation.

Just buying Colvic Countess 33 bilge keel, has been in seawater at Porthcawl last few years and currently has zinc hull anode about 30-40% depleted. Survey picked up minor pinking on prop.....there is currently no shaft anode

She's now on the hard at Cardiff bay where I plan to keep her at least until October then either move to Swansea marina or stay in Cardiff. Both are freshwater I believe with maybe occasional salt input at Swansea???? Shell be on the mooring probably 95% of the time for next year or two i would guess

What would people recommend?....my research suggests replacing zinc with magnesium on hull and adding a collar/ball anode on prop shaft?

I'm an anode newbie never had anything to do with em before!!!
Click to expand...

The "rules" are

Zinc is suitable for salt water only because in fresh, or even brackish, water it becomes coated in an oxide crust which renders it ineffective, even when returning to salt water

Aluminium anodes are suitable for salt and brackish waters but for the same reasons as above not for fresh water.

Magnesium is suitable for fresh water only as it is so reactive magnesium anodes will have a very short life in salt or brackish water.


Provided you only stay in salt water for brief periods , the best bet may be to fit a magnesium anode and accept that it will have a short life in salt water.

OTOH if you have a fixed bladed prop made of manganese bronze there is a pretty good chance you don't need an anode at all if its only the prop it has been fitted to protect. People love to fit anodes and the suppliers love to sell them but in simple cases with decent manganese bronze props they are often not necessary. It's folding props made of a mixture of metals where the fun begins!

Surface pinkiness is nothing to worry about.

Have you actually checked the bonding between your anode and the prop anyway.
 
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I looked into anodes for Cardiff bay a few years ago. I contacted M C Duff and they said the bay was salt or brackish, which is obviously wrong. In the end I went for aluminium with a magnesium one for when I'm on the mooring. Last year, as I planned to spend more time in salt water, I changed to zinc but had to clean off the oxide layer a couple of times. There is no perfect answer, for me one consolation is that our club does not have shore power so less stray current to worry about.
Allan
 
Put aluminium on the sail drive and the three blade folding prop.
Sail drive good for at least another year, prop anodes half gone, but changed them anyway. Mostly due to the stainless bolts holding them on I think!
In and out of the bay most weeks plus usual cruising weekends etc.
 
I was told to use aluminium and after a year they look new, so don't bother with them in Cardiff bay. I would use Magnesium again next time shes out.
 
single said:
I was told to use aluminium and after a year they look new, so don't bother with them in Cardiff bay. I would use Magnesium again next time shes out.
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more importantly what did the material you were protecting look like? if they looked new then some erosion must be taking place to keep them free from oxidisation, and therefore probably balanced with the electrical potential differences involved.
 
Kerenza said:
more importantly what did the material you were protecting look like? if they looked new then some erosion must be taking place to keep them free from oxidisation, and therefore probably balanced with the electrical potential differences involved.
Click to expand...

The rudder had more rust than normal with aluminium, but i think one of the old magnesium type is still protecting the engine/prop etc.
 
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