Question on using a 'dangle' anode

[SVB]

Question on using a \'dangle\' anode

Folks,

I have VP D4's with DP-H legs and have (as it seems most do) problems with corrosion of the props.

To try and help the situation I plan to have a dangle anode lowered into the water between the props when the boat is left on its berth and the anode connected to the battery -'ve terminal.

Now the question. Should I attach the anode via a s/steel wire with an electical crimp OR will S/Steel not conduct well enough and a therefore would a copper wire with a rope backup to take the weight be better? Does it matter?

Thanks in advance.

 

[NorthUp]

Re: Question on using a \'dangle\' anode

Stainless wire will be ok, but much much better if you can find a bolt on the outdrives themselves, or at a push the brackets inside the transom, to connect to.
Any anodes left on the legs, can we asume this is a temp repair until you can lift out?
Make sure the hanging anode is in salt water, if there is a lot of rain, or you are in a sheltered mooring a layer of fresh water can build up on the surface.

 

[VicS]

Re: Question on using a \'dangle\' anode

I believe galvanised wire is recommended. Copper and stainless are at the wrong end of the galvanic series.

MGDuff and no doubt others supply them with a length of wire bonded to them

Not so sure about the battery negative as a suitable place to connect to. Is there a good low resistance electrical path from there to the prop? If the hanging anode is to work it is vital that there is .

Not leaving shore power connected without a galvanic isolator in the system I trust.

 

[SVB]

Re: Question on using a \'dangle\' anode

Thanks for the replies. There is plently of life left in the VP anodes but I am still getting prop errosion (MGDuff confimed this is an known issue as SIBS). This additional adode is an attempt to slow the problem. Interesting post re connection to transom shield rather than battery -'ve which is what I have been recommended to do (I guess assumption is engine is grounded - prop ultimately connected to engine).

VicS - perhaps you could say a little more. Galvanised what as a substrate. Steel wire? Would S/S be a problem as although at opposite end, it would encourage prefertial loss of anode which is what I want. Volume / mass small compared to legs / props although wite is directly connected I will conceed.

Any more thoughts appreciated!

 

[hlb]

Re: Question on using a \'dangle\' anode

Think the thing is, to attach the annode as close as you can to the problem area. In my case I have a spare annode I can conect to both my shafts with jubilee clips. I can then be fairly sure I have a good conection to the shafts and props.

 

[VicS]

Re: Question on using a \'dangle\' anode

[ QUOTE ]
VicS - perhaps you could say a little more

[/ QUOTE ] I was under the impression that hanging anodes were mounted on galvanised steel wire although not certain about that.

I have now discovered that they are in fact on stainless steel wire. Although not mention of that is made on MG Duffs web-pages for leisure craft on the pages under the heading commercial craft it clearly states stainless steel wire.

You want the anode to be consumed preferentially to your drives etc you dont want to promote loss of zinc by other mechanisms. That would happen if copper wire is used. Stainless steel when passivated is in a similar position in the galvanic series to copper and its alloys but under the effect of cathodic protection it looses the oxide film that passivates it and then behaves much like ordinary mild steel. I am not sure if the effect of a sacrificial anode is enough to case that perhaps it is.

Any way I have now established that stainless steel wire is used and that the information on which I based my belief that galvanised wire is used was incorrect.

Regarding the connection to battery negative that may be Ok if there is continuity between engine and drive leg. What is in my mind is the fact that sail-drive legs are actually insulated electrically from the engine. I am assuming that stern-drives would also be insulated, perhaps they are not.

 

[SVB]

Re: Question on using a \'dangle\' anode

VicS - Many thanks - I had not expected you to do more 'homework' but it was very interesting and much appreciated.

I had assumed there was an electrical link from the boat / engines to the drives given all the focus made on here on correct isolating doides when on shore power. Perhaps a call to VP is in order?

 

[neale]

Re: Question on using a \'dangle\' anode

[ QUOTE ]
I had assumed there was an electrical link from the boat / engines to the drives given all the focus made on here on correct isolating doides when on shore power. Perhaps a call to VP is in order?

[/ QUOTE ]

There should be a good electrical link between battery negative and drive/prop. Drives often use small braided s/s wires to get a good connection between parts. These sometimes break and should be checked regularly.

Using a multi-meter you can check resistance between the prop and the point where you wish to bolt the in board end of your dangly anode. Ideally the resistance will be 0.00 ohm although that is very unlikely. It def should be less than 1 ohm though and somewhere around 0.01 and 0.03 ohm indicates good bonding.