Anode or no anode? Bonded or not Bonded, that is the problem!

[haydude]

Every year about this time I read several threads about anodes, galvanic isolators etc. and I wonder if I should worry that my boats have had neither for years. But then I never experienced any damage despite being always connected to shore power.

This year however I have been on a different berth for the last three months, near an old boat that looks like steel. In addition I have just replaced the alluminium propeller with a bronze folding, which makes a significant configuration change to the electrical balances.

My latest boats (a Dufour previously and now a Bavaria) came from factory with VP saildrive, without any bonding at all. The only anode is the saildrive anode.
Both boats electrical systems do not have the mains earth bonded to the keel or the battery negative.

In both cases, after more than a year in the water I always found the saildrive anode very superficially pitted.

Now I have an additional anode on the bronze folding propeller, which is electrically isolated from the saildrive.

I wonder why so many on these forums sound so dooming about GIs and anodes, is this because their boats have earth and battery negative bonded to the keel?

 

[VicS]

I wonder why so many on these forums sound so dooming about GIs and anodes, is this because their boats have earth and battery negative bonded to the keel?

Any problems that arise from the shorepower connection are also the result of the shorepower earth being bonded to the anodes , engine, stern gear, the hull in the case of metal hulls etc including the DC negative except, when the DC system is isolated.

The best wisdom and a requirement of most standards relating to AC shorepower installations is that the shorepower earth should be so bonded although there is the provision in ISO 13297 for the bonding not to be made provided the boat is protected by a whole craft RCD. That is likely to be changed, I am told, when the ISO standard is next revised. It is also contrary to what experts in the field would recommend.

You are therefore rather trapped between the problems the shorepower might cause and the safety aspects of the installation.

There are two solutions. An isolation transformer, preferably on the pontoon, or don't leave the shorepower connected. Boats on swinging moorings don't have shorepower connected all the time !

Every year about this time I read several threads about anodes, galvanic isolators etc. and I wonder if I should worry that my boats have had neither for years. But then I never experienced any damage despite being always connected to shore power.

If your shorepower is not bonded to engine, anodes, sterngear and DC negative etc ensure that you have an RCD in the incoming supply and that you test it for correct operation regularly and relax in the knowledge that you should have no galvanic ( or other) corrosion problems caused by the shorepower connection. You have to accept that your electrical safety provisions may fall a little short of some standards.

If your shorepower earth is bonded then you are lucky not to have any problems. Rejoice but be vigilant.

 

[Bosun Higgs]

Lets go back to basics. Two different metals in an electrolyte ( sea wter will do) make a battery and a current flows through the electrolyte. The current depends on the resistance of the circuit so the further the two metals are apart, the smaller the current flow and the less material is eaten off the anode. So if you have an all bronze blakes seacock you dont need to bond it - no dissimilar metals and no electrical connection. My Prout cat was like that - 20 years without any anodes at all and no problems at all.

What most boats have is a bronze prop on a stainless shaft and hence an anode bonded to the assembly is required to make sure its the anode that is eaten away not the prop. Similar situation with an outdrive leg except there is a lot of vulnerable alloy about.

The problem with shore power is that if you bond in the earth wire you are likely to find your boat electrically connected via the earth wire to all sorts of things from other boats to the pontoons and the piles. Results can be unpredicatble to say the least. Now the H&S types will say your boat must always be bonded and I suppose for ultimate safety no one can argue with that. Personally I leave the 12v and 240v circuits totally seperate with only a battery charger in between - and that has the 12v negative feed isolated from the mains. Undoubtedly it could go wrong but the question is how likely is that? Particularly bearing in mind that most continental mains voltage set ups are two wire anyway. Do you see thousands on foreigners being electrocuted.

As it happens my boat has an RCD anyway. But whilst I cannot recommend you to follow my example, I personally have no worries about the level of real risk |I am taking.

 

[GrahamM376]

The problem with shore power is that if you bond in the earth wire you are likely to find your boat electrically connected via the earth wire to all sorts of things from other boats to the pontoons and the piles. Results can be unpredicatble to say the least. Now the H&S types will say your boat must always be bonded and I suppose for ultimate safety no one can argue with that. Personally I leave the 12v and 240v circuits totally seperate with only a battery charger in between - and that has the 12v negative feed isolated from the mains. Undoubtedly it could go wrong but the question is how likely is that? Particularly bearing in mind that most continental mains voltage set ups are two wire anyway. Do you see thousands on foreigners being electrocuted.

This discussion has taken place on another forum recently where it was obvious I was out of step with the majority, in not bonding everything to shore neutral regardless of what is normal electrical practice. It does appear that some of those who have bonded everything have some galvanic corrosion and rusting keels. Living on mooring or anchor most of the time, I don't have that problem.

I have come across marina supplies which have reversed polarity and certainly don't want the toe rail and everything else to be live - could spoil my day! Hopefully, the RCD should do its job if a fault occurs.

 

[VicS]

This discussion has taken place on another forum recently where it was obvious I was out of step with the majority, in not bonding everything to shore neutral regardless of what is normal electrical practice. It does appear that some of those who have bonded everything have some galvanic corrosion and rusting keels. Living on mooring or anchor most of the time, I don't have that problem.

I have come across marina supplies which have reversed polarity and certainly don't want the toe rail and everything else to be live - could spoil my day! Hopefully, the RCD should do its job if a fault occurs.

No You don't bond anything to the neutral !
You bond it to the earth, ground or protective conductor as it is called these days.

For the reasons you give bonding to the neutral could be very dangerous

 

[GrahamM376]

No You don't bond anything to the neutral !
You bond it to the earth, ground or protective conductor as it is called these days.

For the reasons you give bonding to the neutral could be very dangerous

Quite a lot of people are of the opinion that neutral and earth should be connected - I disagree. This statement is by a guy on another forum - "As quite a few boat mains circuits also connect the boat earth to the neutral, it is worth while checking that live really is live and that neutral really is neutral".

 

[VicS]

Quite a lot of people are of the opinion that neutral and earth should be connected - I disagree.

There are various systems of providing the local earth but the neutral is earthed somewhere before it gets to you ... at the substation or local transformer. You should not then locally link the earth and neutral although in some systems the local earth is a just connection to the neutral.

Well worth checking a marina supply with a simple plug in tester to confirm the correct live and neutral "polarity" and the earth continuity.

Wikipedia describes the various earthing systems if you really want to read all about it.