Spyro
Well-Known Member
Boat was lifted last week. Anyone know why my anode ended up like this. It's been on since April and has only eroded on 1 half.
Propshaft Anode, what happened?
- Thread starter Spyro
- Start date
fluffc
Well-Known Member
Most likely lack of, or poor, electrical bonding between the two.
Or
If these are either side of a rudder (for example), and one is nearer to the metal that is being protected, then one will corrode quicker than the other.
Or
If these are either side of a rudder (for example), and one is nearer to the metal that is being protected, then one will corrode quicker than the other.
ColinHuggins
N/A
Send those pics to M G Duff in Chichester and save us guessing. Do tell us the result tho'.
CJH
CJH
Spyro
Well-Known Member
[ QUOTE ]
Most likely lack of, or poor, electrical bonding between the two.
Or
If these are either side of a rudder (for example), and one is nearer to the metal that is being protected, then one will corrode quicker than the other.
[/ QUOTE ]
This was a shaft anode. so both electrically bonded to the shaft and to each other with the bolts connecting them,
Most likely lack of, or poor, electrical bonding between the two.
Or
If these are either side of a rudder (for example), and one is nearer to the metal that is being protected, then one will corrode quicker than the other.
[/ QUOTE ]
This was a shaft anode. so both electrically bonded to the shaft and to each other with the bolts connecting them,
duncanmack
Well-Known Member
[ QUOTE ]
Boat was lifted last week. Anyone know why my anode ended up like this. It's been on since April and has only eroded on 1 half.
[/ QUOTE ]
I was going to tell you about the shaft anode weevil which has appeared on the Clyde, but I won't.
Seriously. Do I see the head of a S/S cap bolt poking out of the eroded half? And a S/S spring washer?
If so that is possibly the problem.
I got my head in my hands for Not using mild steel fasteners on anodes. Stainless causes all sorts of problems allegedly.
Boat was lifted last week. Anyone know why my anode ended up like this. It's been on since April and has only eroded on 1 half.
[/ QUOTE ]
I was going to tell you about the shaft anode weevil which has appeared on the Clyde, but I won't.
Seriously. Do I see the head of a S/S cap bolt poking out of the eroded half? And a S/S spring washer?
If so that is possibly the problem.
I got my head in my hands for Not using mild steel fasteners on anodes. Stainless causes all sorts of problems allegedly.
Richard10002
Well-Known Member
ISTR that my prop anode came with bolts supplied.... If you're right, I hope they werent S/S, but I think they were??
john_morris_uk
Well-Known Member
Why on earth wouldn't s/s fastenings be ok for the shaft anode? I have used them for years and never had a problem. As far as I recall, all the shaft anodes I have seen come supplied with s/s bolts.
To me it looks as though there was a high enough resistance to the once side to allow only the other to erode. Bit of dirt/oxidization under the bolt heads and between the anode half and the shaft? Its only got to be a small resistance to make it happen.
To me it looks as though there was a high enough resistance to the once side to allow only the other to erode. Bit of dirt/oxidization under the bolt heads and between the anode half and the shaft? Its only got to be a small resistance to make it happen.
cliff
Well-Known Member
Initial response would be you have two different alloys there. Could have been two different castinging batches with different composition hence one side corrodes while partially protecting the other. There are other possible causes but if you are worried I would contact MG Duff assuming the anode was one of theirs and not a cheap copy.
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"Artificial intelligence is no match for natural stupidity"
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boatmike
Well-Known Member
I was going to say the same thing. Presumably they wouldn't have to be vastly different in composition for this to happen. I would also ask if the two halves were making proper electrical contact with the shaft as I have seen people bolting them over dirt, corrosion and even antifoul in one case. Granted the two are electrically connected by the bolts but possibly also with a resistance.... If current flows more easily one side than the other would this not do it too Cliff?
Aja
Well-Known Member
One half magnesium, one side zinc? Manufacturing problem?
Donald
Donald
cliff
Well-Known Member
[ QUOTE ]
I was going to say the same thing. Presumably they wouldn't have to be vastly different in composition for this to happen. I would also ask if the two halves were making proper electrical contact with the shaft as I have seen people bolting them over dirt, corrosion and even antifoul in one case. Granted the two are electrically connected by the bolts but possibly also with a resistance.... If current flows more easily one side than the other would this not do it too Cliff?
[/ QUOTE ]Hmmm, I would have to reserve judgement on that one - we are talking micro amps so I would not expect such a big difference in corrosion rates. I just looked at the photos again and there appears to be a void in the "good" half which would lead me to suspect a dirty casting or improper cooling rates. It could have been cast in a very hot mould resulting in a slow cooling rate and and a course grained dendritic structure resulting in preferential corrosion occurring. There are a number of things that could affect the anode performance but without actually seeing the pieces and carrying out a few tests I would not like to pass judgement - I would still be interested in MG Duff's theory/comments.
--------------------
"Artificial intelligence is no match for natural stupidity"
sailroom <span style="color:red">The place to auction your previously loved boatie bits</span>
I was going to say the same thing. Presumably they wouldn't have to be vastly different in composition for this to happen. I would also ask if the two halves were making proper electrical contact with the shaft as I have seen people bolting them over dirt, corrosion and even antifoul in one case. Granted the two are electrically connected by the bolts but possibly also with a resistance.... If current flows more easily one side than the other would this not do it too Cliff?
[/ QUOTE ]Hmmm, I would have to reserve judgement on that one - we are talking micro amps so I would not expect such a big difference in corrosion rates. I just looked at the photos again and there appears to be a void in the "good" half which would lead me to suspect a dirty casting or improper cooling rates. It could have been cast in a very hot mould resulting in a slow cooling rate and and a course grained dendritic structure resulting in preferential corrosion occurring. There are a number of things that could affect the anode performance but without actually seeing the pieces and carrying out a few tests I would not like to pass judgement - I would still be interested in MG Duff's theory/comments.
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sailroom <span style="color:red">The place to auction your previously loved boatie bits</span>
nedmin
Well-Known Member
Stainless shouldnt be a prob. my steel boat has stainless bolts welded onto the hull and the anodes fastened to them. the wear is telling you where the current is coming from,do you know which way round it was? could be another boat causing stray currents.
Spyro
Well-Known Member
I used the nuts and bolts supplied with the anode no spring washers, don't see the problem with S/S bolts as it's attached to a S/S shaft. The anode was purchased at the chandlers out of a box of them so don't know if it was from MG Duff or not. I'll try send them the pic anyway.
I suspect that it is more likely that the 2 half's are from a different batch with a slightly different composition of zinc.
Thanks for the interest so far.
I suspect that it is more likely that the 2 half's are from a different batch with a slightly different composition of zinc.
Thanks for the interest so far.
charles_reed
Well-Known Member
Two Possibilities
Most likely - difference in alloys used in manufacture
Less likely - one half insulated from prop-shaft.
Most likely - difference in alloys used in manufacture
Less likely - one half insulated from prop-shaft.
TheBoatman
Well-Known Member
Why Does Anybody Use!
Prop shaft anodes.
IMHO they are the worst invention ever - if they work then they only serve to unbalance the prop shaft during use.
They're so small as to need replacing on a regular basis.
They tend to come loose, leading to vibration when under power.
Fall off because their "knackered".
Why not take the plunge and do the job right - get a decent sized couple of hull anodes and wire them up correctly and forget those dam shaft anodes.
Blo**y things aren't worth the time, effort or money!!!!!
Peter.
Prop shaft anodes.
IMHO they are the worst invention ever - if they work then they only serve to unbalance the prop shaft during use.
They're so small as to need replacing on a regular basis.
They tend to come loose, leading to vibration when under power.
Fall off because their "knackered".
Why not take the plunge and do the job right - get a decent sized couple of hull anodes and wire them up correctly and forget those dam shaft anodes.
Blo**y things aren't worth the time, effort or money!!!!!
Peter.