Do anodes work if covered in weed?

[Garold]

I've just got a diver down cleaning the bottom of my boat and checking the anodes.

I had the boat anti fouled and new anodes fitted in May but since the waterline looked dirty I thought that underwater may be the same. I also wanted someone to take a look at my anodes.

The diver told me that given that it is only 6 months since I had the bottom cleaned and anti fouled, it is pretty dirty. He also said that the anodes can't be working properly because they are coated in weed.

I have felt a couple of the anodes becasue they are near the surface and they are a bit pitted so I assume that they are doing their job. However, I'm just wondering if the diver has a point.

Is a weedy anode a sign that they are not working properly? Are they effective when weedy or should I make an effort to keep them clean somehow?

Cheers

Garold

 

[V1701]

I'd have thought at least less effective but what can you do, not as if you can antifoul them! I've also seen anodes covered completely in a white chalky/calcium like deposit that I have assumed renders them ineffective and scraped it off, this was when I was diving under a friend's boat to clean and check anodes...

 

[VicS]

Weed will reduce the effectiveness of the anodes to some extent

BUT I wonder if the fact that they are covered in weed indicates that they are not actually doing anything.

What are they fitted to protect and how are they bonded to the item(s) they are supposed to be protecting.

I think I would check the bonding as well as cleaning the weed off. There must be a good low resistance electrical connection.

 

[Garold]

We have one anode on each stern drive just in front of the props. These are standard Yanmar fit and proved to be inadequate last year.

We have also had one extra (larger) anode fitted to each hull near the stern drives and these were fitted and bonded to the engines by a qualified marine electrician.

I'd hope that our retro fitted extra anodes are correctly fitted and are doing some kind of job. They are a bit pitted after 5 months in the water so they must be working somewhat.

However, the diver unnerved me when he said that the anodes can't be working properly covered in weed.

Mmmmh, it feels like the management of electrolysis on boats is an opaque science.

Cheers

Garold

 

[Vara]

Umm, I'd share the concern that it is not bonded to whatever it's protecting.

As I've never seen weed on an anode.

I would do some continuity checks.

 

[AntarcticPilot]

There appear to be several issues here:

1. Does weed on an anode signify it isn't working?
2. Does weed on an anode STOP it working?
3. Does the build up of a chalky layer on the anode reduce its effectiveness?

As far as I can see, the answer to all is a qualified "No".

First of all, an anode does not and is not intended to have any effect on biological fouling. The idea is that the anode corrodes away preferentially to any metal of lower electrochemical potential that is in circuit with it. An anode has no effect whatsoever on biological fouling. So, the presence of weed on an anode does NOT signify that it isn't working.

Second, as long as the circuit of seawater, anode and protected metal is complete, the anode will do its job. Again, weed or other fouling will probably not affect this very much, though perhaps very dense fouling might break the contact between anode and sea water.

Finally, the chalky layer that forms on an anode is a sign it IS working; it is basically the "rust" that forms on the anode, saving deterioration of the protected metals. It will be pretty porous, so it will not stop the anode working immediately. However, presumably too thick a layer could stop the anode working, so I guess that as long as there's plenty of metal left on the anode, it might be worth chipping the chalky stuff off.

 

[prv]

So, the presence of weed on an anode does NOT signify that it isn't working.

It doesn't directly, but if the anode is eroding properly then will weed be able to stay attached? I don't know either way, but it's a plausible explanation for the "weed shows it's not working" idea.

I guess that as long as there's plenty of metal left on the anode, it might be worth chipping the chalky stuff off.

I generally give it a good wire brushing, never needed to chip it.

Pete

 

[AntarcticPilot]

It doesn't directly, but if the anode is eroding properly then will weed be able to stay attached? I don't know either way, but it's a plausible explanation for the "weed shows it's not working" idea.



I generally give it a good wire brushing, never needed to chip it.

Pete

Good question, to which I don't have a definitive answer; my guess is that it probably depends on the rate and type of the corrosive processes - slower corrosion will probably deposit a denser layer that is less likely to flake off, for example. On my anodes, the corrosion products tend to form quite a hard layer, which I'd imagine would make quite a good substrate for marine organisms if I were in an area with heavy fouling.

I am fortunate - anodes last at least two years on Capricious, and the fouling where I am is very light!

 

[PaulJ]

For what it's worth, on my steel boat the anodes seem to be working well........ the prop has no dezincification and the anodes get steadily eaten away. Each season they get a lot of weed and white chalky stuff on them but they seem to be doing their job.

 

[maby]

All good advice given above, but one important suggestion is missing - dangle an auxiliary anode when you are not sailing the boat...

Get one of those large teardrop anodes that is moulded onto a steel bar with mounting holes drilled at each end. Solder a reasonably thick wire to the steel bar - if you clean it up well and apply a bit of flux, ordinary solder will take easily using a small gas blowtorch. Once you've soldered the wire to the bar and it's all cooled down, tie the wire through the mounting hole on the bar so that the weight is not being carried on the soldered joint alone.

Find something metallic in the locker that is tied to earth. I actually ran a wire directly from the negative connection on the battery out to a terminal that I fixed inside the cockpit locker. Connect your new anode to the boat earth and dangle it over the side into the water - take the weight on a cleat or other suitable support. It will take some of the load off the permanently mounted anodes and extend their life. It's also easy to pull up, inspect and clean - well worth the £15 or so it will cost to make up and the half hour or so it will take.

 

[Red Admiral]

I have three anodes, one teardrop bonded to stern gear and two large button anodes bolted to the iron keels. Even though the tear drop disappears much more slowly than the others, none ever has any weed on it. I don't believe any weed can take root on a surface which is constantly being destroyed, ie weed means no effective protection!

 

[Bobobolinsky]

That's not to say that it is not going to work if required. It may also be that the boat is over anoded, which can also cause problems. Don't forget that like FM radio waves anodes are "line of sight", and in addition need to be within 1 metre of the item to be protected. Unfortunately you can't easily test anodes, but they should be generating +800 to 850mA to make them effective. This can also be done electronically without using sacrificials. Typically if a boat is overprotected, it can blow off the coatings applied to metallic parts, then they work really hard