When to replace the Anodes ?

[Dave-Fethiye]

Hi,
I have taken off the two anodes that were on the stern near the propellor
and have cleaned them up. They both had a layer of about 2- 4 mm white oxide on them. Now that I have cleaned them up they are still a bit pitted but are the grey color.

These things are made of lead I guess ?

The person who was going too do the work said that they need replacing ( but I think he was after some extra work !)
The size of these anodes is only slightly less that new ones - so do they still have usefull life left in them ?
When do you replace them - when they get a lot smaller ?

Will appreciate any help.
Thanks.
Dave
Fethiye
Turkey

[Alan Wheeler]

Yes replace them. Firstly, normal service is to replace them one per year at every haul out. They are Zinc by the way.
Now to your two anodes. They should not have the white powder (Zinc oxide) on them. This can be caused by several factors. Poor Zinc quality is the least usuall, but possible. The more probable are, poor anode connection to the hull leaving the anode not working. Or more commonly is over Zinc'd. That is having too much Zinc to do the work. All situations are bad and need solving. Firstly you need to ensure the anodes are bonded to the metal.
When you place the boat back in the water, you need to do some testing. Get a Marine sparky to take alook. He needs to test the current flow for protection. That flow needs to be within a specific range for adiquate protection. Too much or not enough will both cause damage. You need to then add or subtract anodes to get the current in the right range.

[Dave-Fethiye]

Thanks for the input,

A marine sparky said that the anodes should to connected to the engine to prevent the alumium casings from oxidising ( white powder formations).

The engine though is connected to the -ve on the bgattery banks. So is this really a good idea ? Should the engine and sacrificial anodes all be connected to the battery bank ( -ve side) ?

[seafox]

When you clean the metal under the anodes, only use emery cloth. Sandpaper can leave a residue that can form a galv reaction with the anode.

[Dave-Fethiye]

Well I used a wire brush and scraper.
I have bought a new one that I will connect up to the others with some copper wire.

What about this battery connection idea ?

[Alan Wheeler]

Yes it all needs to be tied together. The -ve of the batteries should be and on ly be connected to one point on the egine block. Usually close to the starter motor. All earths go to this point. It doesn't matter where your anode is tied back to. Getting it back to the engine can be difficult. So as long as it is in contact with the engine via underwater fittings. I assume seeing as you mentioned underwater casings, that you have stern legs?? If yes, is it one or twin legs?? Please give a little more detail of the setup, it is important as to how to do this.

[fstbttms]

Zinc anodes should be replaced when they are 50% depleted. Although I am in the business of selling and replacing them, I tell you in all honesty that it is the rare boat that can go a year between zinc replacements (at least here in California.) Not sure what Alan means by "normal service" but in areas where haul outs do not occur annually and boats receive in-water cleanings, it usually falls to the diver to make sure the boat in question is properly zinc'd.

[Alan Wheeler]

Fstbttms is right. It depends on where the boat is. Salinity, sea temp, electrical issues in the marina, how much metal and even the types of metal needing protection all have a bearing on how fast an anode will deplete. I am lucky that I can get a year from mine because we have big flushes of fresh water through on regular intervals. This means the Salinity can decrease rapidly and thus an anode can last much longer.
For most in NZ, a yearly haul out is usually OK for anode replacement. If you can't make a year, then the anode was on the too small side to begin with. But the Salinity and water temp is a lot lower here in NZ.

[seafox]

My new volvo has three small anodes on the three prop blade (the anodes form a circle) and one very large on between the prop and the blade. The three small ones last about 6 months but the big sucker has been on a year and wouldn't be 10 percent depleted. Has a bit of pitting but nothing near 50%. I reckon I will get 18months to 2 years from it.

[Alan Wheeler]

Ensure it is working Darryl. Keep an eye on it. It can go the otherway as well. If it is too big or not working for some reason, it will eventually gain a white crusty crud on the surface of it. A working anode should be slightly dark grey'ish, not shiney and a black substance should rub of onto your hands.

[seafox]

it's fine. It is the standard Volvo one that comes with the motor. No white crust. Just a lot more zinc that the old model. I think that the smaller ones get hammered worse though

[Dave-Fethiye]

Thanks for your replies.
I bought a nice new shiny anode. But the two anodes that I took off are only maybe 10 % depleted. One had some white crust on - so I guess that means that the connections to it were not good.
( "not working" can only mean bad connections right? )

I have cleaned up the old ones and am thinking of connecting them back up with new copper wire.

Is there any harm in having too many anodes ( I can't see any - would just mean that they all deplete more slowly - right ?)

[Alan Wheeler]

No you can have too much anode. It is just as bad as not enough. Too much anode can also cause the white crust.

[Idiens]

Originally Posted by Dave-Fethiye

T
Is there any harm in having too many anodes ( I can't see any - would just mean that they all deplete more slowly - right ?)

The more the better if they are connected properly.
You didn't mention if you are in salt or fresh water. In fresh water you need aluminium anodes instead of the zinc ones for salt water. Zinc will grow a white oxide in fresh water and stop working.

[Dave-Fethiye]

I am on the Turkish south-west coast, so warm salty water.

We seem to have a dis-agreement about having too much anode !!

Who is correct - can't be both

Thanks