Do my anodes get eaten if.....

Well galvanic currents are generated wherever you have dissimilar metals in an electrolyte, so I think your anodes will get eaten under those conditions, but unless something is seriously amiss they probably won't get eaten very quickly.
 
Yes, a zinc anode will, other metals, more noble, such as copper, may not. If an outside voltage is introduced then more noble metals will corrode. That's how I understand it.
 
They better do because that is a sign that they are giving their ions to the nobler metals around them instead of your bronze seacocks and prop.That is what they are supposed to do hence the name sacrificial.What can happen is that if you have residual currents created by shore power or having the batteries on the wear might be accelerated.It can very rarely happen that the metals in your boat balance perfectly and thus no flow of electricity is generated but that is very improbable.There are other more knowledgeable than me here who can explain this better.
 
May, or may not depending on what they are connected to. The typical problem is props and shafts where a galvanic cell may be set up between the two dissimilar metals in contact with seawater as an electrolyte. The prop suffers as it dezincifies so you connect it to a zinc anode which erodes instead. Erosion can also occur through stray electrical currents from shore power, but can be avoided usually by fitting a galvanic isolator.

More information on the MG Duff website.
 
santavey said:
I am not connected to shore power and boat battery turned off?
Boat GRP with bronze prop.
Tried searching...cant find the answer.
Click to expand...
Yes. The bronze prop will be busy creating reacting with the stainless prop shaft and thus creating a voltage. Then you have things like your skin fittings, your keel, the rudder stock. And that's just what's on the boat. You might also have stray currents from the pontoon electrics if you're in a marina.

You might find that the anodes last longer without shore power and the batteries off though but it won't stop them dissolving all together.
 
santavey said:
I am not connected to shore power and boat battery turned off?
Boat GRP with bronze prop.
Tried searching...cant find the answer.
Click to expand...

Yes the anodes will slowly be consumed if they are doing what they are fitted to do.

They should not be consumed any quicker if the battery is switched on.... you have a problem to solve if they are

Similarly you try to avoid increased rate of consumption due to a shore power connection by fitting a galvanic isolator in the shorepower earth connection.



Some useful reading on the subject at http://www.mgduff.co.uk/leisure-craft/cathodic-protection.html

Ans some more in depth reading on the National Physical Laboratory website at http://www.npl.co.uk/upload/pdf/cathodic_protection.pdf
 
I thought a GI was only useful if the shore-power earth was connected to the battery negative? If they're not then there's no stray currents surely?
 
I do not use shore power unless on board.
With my old aluminium prop i rarely changed any anodes
With my brunton autoprop on my sail-drive i change both prop & sail-drive anodes every year as the prop anode disappears & the sail-drive anode looses 50%
 
santavey said:
I am not connected to shore power and boat battery turned off?
Boat GRP with bronze prop.
Tried searching...cant find the answer.
Click to expand...

Short answer :YES

The shore power connection is but one way of many for anodes to be eroded. The battery is another of many, just eliminating (or thinking you have eliminated) two of many wont prevent the possibility of anode erosion. All you need is two dissimilar metals somewhere on the boat, as I have found and they don't even have to be under the water.
 
Marsupial said:
Short answer :YES

The shore power connection is but one way of many for anodes to be eroded. The battery is another of many, just eliminating (or thinking you have eliminated) two of many wont prevent the possibility of anode erosion. All you need is two dissimilar metals somewhere on the boat, as I have found and they don't even have to be under the water.
Click to expand...

Please explain how another (dissimilar) metal somewhere on the boat not under water could cause loss of zinc from the OP's anodes.
 
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