I don't have Anode; Do I need one?

[Refueler]

Re: I don\'t have Anode; Do I need one?

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I am now creating a circuit ... seawater inlet ... shaft ... prop to sea again

[/ QUOTE ] But why do you have your seawater inlet bonded to the shaft?

Even if you do and the inlet seacock is close enough to the stern gear it is presumably also bronze and as a result there is still no threat yo your lovely prop.

Best advice with bronze seacocks is not to bond them to anything else.

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The connecting medium is not the seacock - its the seawater itself travelling up into the engine. Seawater is a good conductor unlike FW.

Further - I regard my safety as paramount and all on board ... bonding seacocks is not on my list.

 

[Refueler]

Re: I don\'t have Anode; Do I need one?

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Hi ,
Slightly different question but still anode related – I have recently fitted a galvanic isolator to protect my boats anodes whilst on shore power but even with that it seems my shaft and transom anodes are disappearing very very quickly ( I will be lucky if they last 3 months at this rate ) . The anodes fitted are McDuff zinc so quality shouldn’t be an issue.
Of course I would be really worried if my anodes weren’t wasting at all but the rate compared to another similar size boat sitting beside me at the Marina is startling.
Any ideas why ? is there anything I can do about it ?

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It can be due to inter-action between two vessels - one becoming sacrificial to another. Particularly if connected to same mains power supply etc.

 

[vyv_cox]

Re: I don\'t have Anode; Do I need one?

<<< The connecting medium is not the seacock - its the seawater itself travelling up into the engine. Seawater is a good conductor unlike FW. >>>

Sorry, just not true. Seawater is not a great conductor, it has quite high resistance, but that isn't particularly the problem here. Current likes to travel in a more-or-less straight line in water, it doesn't go round curves as if a hose was a wire. MGDuff say that anodes should be 'line of sight' for this reason. There is a slight tendency for the current to creep around the back of a line of sight object but there is no way it will go along a hose.

Added to that, how is it going to get through the seawater pump?

 

[VicS]

Re: I don\'t have Anode; Do I need one?

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Any ideas why ? is there anything I can do about it ?

[/ QUOTE ] Possible that your GI is not performing as it should. Has it been subjected to any major fault currents that could have damaged it? Are you sure the GI is correctly connected and that it is not inadvertently being bypassed. It seems odd that fitting one has not improved matters.

There was some information posted recently about how mains equipment with switched mode power supplies can send a current down the earth connection. This can lead to the GI being in a conducting condition and therefore not blocking the currents from galvanic sources that cause rapid wastage of anodes. The solution apparently is a capacitor in parallel with the GI. I don't know how to calculate the required size though.

Until recently I argued in favour of the shorepower earth being connected to the boats DC system earth, ie the anodes etc and the DC negative. However I have recently discovered that ISO 13297 does not require this if the whole mains installation is protected by an RCD (It is still a requirement of the ABYC standards though). If the shorepower earth and the DC earth are not interconnected it should eliminate galvanic corrosion problems cause by the shorepower system and the need for the GI.

While I think I would not now connect the two together myself I am still sitting on the fence rather when it comes to suggesting what others should do. There was a lengthy article in Professional Boatbuilder magazine by Nigel Calder about 3 years ago to which a link was recently posted. I still have to find the time to read that before deciding on which side of the fence I should descend. If you feel happy about it disconnect the shorepower earth from the dc earth and anodes etc. but be sure the RCD works if you do.
Alternatively, if you can, unplug your shore supply and see if it improves the situation. If it does then the problem lies with it. Otherwise the problem is elsewhere and maybe something you have to live with

Sorry half a page of waffle, not much sound advice. .