Cathodic protection???

[bammylovechops]

Hi,

I have seen a in our marina a few boats with what looks like some form of cable or chain dangling in the water, looks about 6mm in diameter, usually from the bow. It was mentioned that it is something to do with helping to prevent erosion of anodes. This is apparently done by connecting old anodes to to water end of the cable/chain and the other end to the main 230v side of the earth.

Can somebody shine any light on this or is it a myth, if it is correct please explain how to do it.

For info I already have a cathodic protection device fitted.

 

[VicS]

Hanging anodes possibly, but they should normally be hanging close to some vulnerable thing such as an outdrive leg in order to supplement the protection from fitted anodes and with luck also prolong their life. From the bow would not be the place to do that! Although perhaps hung there to protect a bow thruster.
The inboard end of the cable would best be connected directly to the item to be protected although if this is electrically connected to the DC negative and the boats internal earthing system a connection to a suitable point on the earthing system could be used.

Hanging anodes can be bought with a length of stainless steel wire attached.

What problems do you have that you think might be solved by using a hanging anode?

They are popular with owners of aluminium hulls where several might be used to enhance the protection of the hull.

If you have a shore power installation and normally leave it plugged in (not necessarily in use) then the almost essential bit of equipment to have is a galvanic isolator ... at least if the shore power earth is as it should be connected also to the DC negative and the boats earthin system.

 

[bammylovechops]

Hi Vics,

Thanks for replying.

I do not have any problems at all, is was perhaps a belt and braces approach to see if a simple thing like using old anodes would help extend the life of the existing anodes. As this is a new boat to me, I will be unsure of the condition of the anodes until the next lift, but the anodes that are currently installed are new.

My boat in usually left plugged into the mains electricity most of the time to keep batteries charged etc.

So do you think it is a worth while thing to do?

Mark

 

[VicS]

If your boat is plugged into shorepower then,as I said earlier, a Galvanic isolator could be the most important thing to have fitted if you do not already have one, although it does depend upon whether or not the shorepower earth is connected to the boat's earth and DC negative or not. Whether it should be has been a topic of appreciable debate but the current advice from the experts in the field is that it should be.
However, the current version of the standard relating to electrical installations in small craft, ISO 13297, does allow the connection not to be made provided the whole craft is protected by an RCD but I have been told that exception is unlikely to be included in the next revision.

The trouble once the earth connection is made is that your boat is then connected , via that earth connection, to all the other boats in the marina and also probably to the piling and pontoons as well. The result can then be that small currents from galvanic ( dissimilar metal) sources can be eating away at your anodes. A galvanic isolator blocks these currents but allows currents from high voltage sources to pass, so maintaining the safety benefits of the earth in the shorepower supply.

Adding hanging anodes may help to reduce the rate of loss of your anodes. They are often added when boats are fitted with outdrives and sail drives etc as a belt and braces policy. Often people find that the fitted anodes are lost at a faster rate than they are prepared to pay for haulouts to inspect or replace them on such drives . They then still have the protection of the hanging anodes even if the fitted anodes become completely consumed before the next scheduled haul out.

 

[bammylovechops]

Hi VicS,

Yes I do have a pair outdrives. I also have 3 or 4 old but still in reasonable condition anodes sat in the garage doing nothing.

In your opinion what would be the best/most effective way to utilise them, from the beginning please, including both ends of the cable, please bear in mind that I do have a decent galvanic isolater already installed.

My berthing arrangments are that of a typical marina, but I am birthed six feet away from a steel pencil.

Regards

Mark