Pear Anodes

[davidmh]

This is a question for the chemists among the forum.
At the end of the season the sacrificial hull anode has some areas where which have become pitted and are a grey colour as you would expect. Large areas are covered with a white deposit the area is also pitted. You can scrape the deposit out of the pitting. What is the white deposit and is there a simple substance that will dissolve the pitting. I presume that this white deposit will stop or reduce the anode performance. Boat in sea/brackish water and hull is GRP.

David MH

 

[ChromeDome]

I check anodes by weighing them because they may look better than they are.
If less than 50% of the original weight I replace them.

 

[vyv_cox]

Zinc anodes develop a coating of zinc hydroxide in fresh and brackish water. This can be abraded off using abrasive papers, not wire brush or a file as iron inhibits their function.

By far the best answer is to switch to aluminium for a whole raft of reasons. See my article here Anodes

 

[alahol2]

I get the same/similar in sea water. I normally chip off the white bits with an old screwdriver and hammer. A pear anode normally last me for two seasons.

 

[davidmh]

Zinc anodes develop a coating of zinc hydroxide in fresh and brackish water. This can be abraded off using abrasive papers, not wire brush or a file as iron inhibits their function.

By far the best answer is to switch to aluminium for a whole raft of reasons. See my article here Anodes

Thanks for your info VYV,
The duff zinc anode I use is 2.1 kg, I see the aluminum equivalent is 1 kg, does this give about the same life as the 2.1 kg zinc. Costs are similar
david MH

 

[VicS]

Thanks for your info VYV,
The duff zinc anode I use is 2.1 kg, I see the aluminum equivalent is 1 kg, does this give about the same life as the 2.1 kg zinc. Costs are similar
david MH

Vyv quotes capacity figures on his website of 780 amp.hour/kg for zinc anodes and 2700 amp.hr/ kg for aluminium anodes

This means that your 2.1 kg Zn anodes have a capacity of approx 1600 amp.hr while a 1 kg Al anode will have a capacity of 2700 amp.hr

You say the price is similar therefore the Al anodes are a better buy by a factor of 1.7.
This agrees with a theoretical figure I calculated before I looked at Vyv's figures