Hull anode bonding systems

[hairbox]

Hi everyone

Can anyone out there give me any advice on the following please

My boat which is a Bavaria 40 year 2001 has had a hull anode bonding system fitted from new by the previous owner. This was installed by the boatyard as it was included in the extra's price list, it comprises of a pear shaped zinc anode attatched to the hull which is then connected to the gearbox and all the skin fittings.

When I said all the skin fittings were connected this is not quite true as the two sink drain skin fittings in the galley are not connected.


Questions

1) Any reason why the skin fittings in the galley are not connected as they are made of the same material etc ?

2) Is it bad practice to connect to the gearbox, as in the volvo handbook it states that the engine/gearbox should never be connected, any reasons as to why this has been done .



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[LadyInBed]

1) If the galley skin fittings are above the water line then they don’t need bonding.
2) I don’t understand this one. Metal engine bolted to metal gearbox - that makes them electrically connected in by book! Unless they mean that the engine / gearbox assembly should not be part of the anode ground system. Then the Battery, Alternator, Starter motor and instruments make a separate isolated circuit, I didn’t think that was normal. To say nothing of the propshaft.


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[MainlySteam]

Without detailed knowledge of the boat it is difficult to be specific. If you get someone to look at it, which you should do if you have any doubts, make sure you get someone really knowledgable in the matter, not the local marina witchdoctor of which you will find there are plenty on this subject. It sounds, but may not be so, that the protection is something that the previous owner, not Bavaria, thought was a good idea. I personally would have stuck with Bavaria's solution unless service in other boats had proved it incorrect.

The Thru Hulls

Any stand alone item under the waterline, not electrically connected to another, which is naturally corrosion resistant eg a good bronze and does not incorporate dissimilar metals inclined to galvanic action between them does not need protection as they cannot form part of any electrical circuit with another dissimilar metal ie they therefore do not need bonding to any anode. If they are unecessarily bonded the likely result is that you will just erode your zinc anode more quickly (and despite many claims by amateurs to the contrary, just because an anode is eroding does not mean it is protecting anything) and, if they are far away from the anode any protection, should it have been necessary, will be limited.

In your case it is possible, if the boat has an AC electrical system that some thru hulls (I am assuming they are metal and not plastic /forums/images/icons/smile.gif) have been bonded just to form part of the AC earthing system.

The Engine and Gearbox

A likely reason for Volvo Penta's comment is that your engine is one which is DC isolated ie all the sensors, the starter and the alternator frames are isolated from the DC negative (unlike a car engine, and many older marine engines). Two matters come to mind if you then ground connect the engine/gearbox to a bonding system.

1. You are implicating the boat's galvanic protection in that of the engine's own protection (and some engines have no protection and need none) and this creates a situation outside of the engine manufacturer's control.

2. An advantage of an engine which is DC isolated is that a broken alternator or starter positive lead, an internal short to frame in those, etc is safe as the engine and its mounted auxilliaries are not part of the DC system so no arcs, etc can occur. However, if the engine is connected to the bonding system, and that bonding system is also connected to the DC negative bus as they commonly are (in my view they should not be though) then this integrity against shorts at the engine is negated as current can now flow from a short to the block or internal or external short to an auxliary frame (eg alternator or starter) back through the bonding system to the DC bus.

As I say, without knowing full details, one can only suppose what the reasons are - the above may be all or some of those.

John

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[steve_cronin]

Drop whatever you are doing!

...and gert down to your boat with some wire cutters!

If your saildrive is connected to the bonding ring and this includes normal zinc anodes and possibly connected to the negative and/or the engine, you could be looking at a very expensive gearbox replacement. I think that the other posters may not be aware that our Bavarias (mine is a 42 of the same age) have saildrives. Saildrives need to be electrically isolated from the rest of the system and this is achieved by a nylon device between the flywheel and the first motion shaft of the drive leg. There are also insulators in the control cables. I once saw a boat where the owner had used a convenient bolt on his saildrive to earth his navtex. within a year the gearcase of the saildrive was badly eaten away and the boat is still (as far as I know) awaiting parts.

The correct way to set up the bonding system on your Bavaria is to link ALL the skin fittings with 4mm copper wire daisy-chaining between all eight of them. (Yes the sink drains although above water at rest are well submerged on a stbd tack) On mine we have used SS jubilee clips around the threaded shanks of the fittings tightened onto well greased bared wire ends. Because we have an large inverter and an SSB radio, we also have a ground plate and this is included in the loop. A galvanic isolator connects the boat earthing system to the shorepower earth by splitting the incoming cable just before the distribution panel. These are relatively rare on UK boats but in the USA they are compulsory for safety reasons. Their main benefit though is in isolating you from other boats in a marina (& the pontoons themselves) to avoid making a galvanic cell through the shorepower.

Your saildrive needs to be completely isolated from the above system as it relies upon it's own anodes. One is the prop spinner and the other is a ring on the lower case just ahead of the prop.

A new gearcase is around £3200 and the above mentioned damaged boat is on the hard at Gouvia Marina Corfu for all to see.

Steev Cronin



<hr width=100% size=1>The above is, like any other post here, only a personal opinion

 

[tome]

Re: Drop whatever you are doing!

<The correct way to set up the bonding system on your Bavaria is to link ALL the skin fittings>

Where on earth (!) are you coming from with this statement, and why does a Bavaria differ from any other boat? Perhaps there's a metallic pigment in the layup, we need to know!

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[MainlySteam]

Re: Drop whatever you are doing!

I think that the scenario that you set out with the saildrive casing is only to be experienced if the DC negative bus is bonded to the galvanic protection bonding (which as I say in my post I do not promote), and there is also a DC electrical fault implicating the saildrive in its return to the negative bus. That is assuming there is no large mass of more noble metal nearby also bonded (which would seem unlikely in a sail drive boat).

Putting that to one side I am in agreement that one should be careful and knowledgable before implicating aluminium into the bonding system and in the case of plastic boats they should, if possible, be left floating with their own independant protection. The problem would not exist at all if the boat was not bonded and it is easy to build a plastic boat so that is so.

{Edit: on reflection, can it be taken from your post where you say that you did the bonding in your boat that Bavaria designed the boats as unbonded?}

Regards

John

<hr width=100% size=1><P ID="edit"><FONT SIZE=-1>Edited by MainlySteam on 25/03/2004 11:03 (server time).</FONT></P>

 

[steve_cronin]

Re: Drop whatever you are doing!

Just simply, if you want to prevent corrosion of metal objects in salt water from any source, connecting them to a sacrificial anode will accomplish this and unless you want to fit an anode to every fitting individually, then a bonding system connected to a common anode is the way to do it.

Are you suggesting that I've wasted my time over 30 years and four boats?

Steve Cronin



<hr width=100% size=1>The above is, like any other post here, only a personal opinion

 

[steve_cronin]

Re: Drop whatever you are doing!

No criticism of your post intended. in fact I havn't read it.


As to " {Edit: on reflection, can it be taken from your post where you say that you did the bonding in your boat that Bavaria designed the boats as unbonded?}" I wouldn't say that Bavaria "designed the boats as unbonded" more like it was another item that the economics of volume boat building require to be omitted.

Steve Cronin




<hr width=100% size=1>The above is, like any other post here, only a personal opinion

 

[MainlySteam]

Re: Drop whatever you are doing!

Oh, I didn't read your post as being criticism Steve, was just interested in the saildrive and aluminium bit.

Regarding thru hulls in a plastic boat there is no need to bond them, nor any need to seperately anode protect each one unless they are of an inferior metal (such as a brass which is inclined to dezincify) or they or any attached valve contain galvanically incompatible metals (which should not be so in correctly selected equipment). In many cases they will be far enough away from the anode that the protection will be suspect in any event.

If they are bonded, one will create a battery and current will flow in the bonding circuit which may cause other problems and at best just needlessly erode the zinc anodes. My own view is that one should strive to avoid stray currents in the marine environment, regardless of whether those currents are caused by electrical leaks or by unnecessary protection with zinc.

John

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[tome]

Re: Drop whatever you are doing!

On my boat, the gearbox is galvanically isolated from the engine. The anode is connected to the gearbox, there are anodes for the shaft and propellor. Neither the bronze P- bracket nor any of the seacocks are connected to anodes, and this is in line with the manufacturers recommendations.

So I think beware of sweeping statements.

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[Twister_Ken]

Galley Skin fittings

My boat: 23 years old, GRP. Proper bronze seacocks (Blakes) and skin fittings. Not bonded. Never replaced. No corrosion.

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[steve_cronin]

Re: Drop whatever you are doing!

On my last boat the P bracket and a couple of metal combination seacocks were de-zincified badly after only one season afloat so I introduced the bonding system after replacement. When it was sold the marine surveyor congratulated me on the bonding system. Better safe than sorry.

Anyway the issue here is a saildrive (& maybe who knows what else) connected to a hull anode and that ain't good.

Steve Cronin

<hr width=100% size=1>The above is, like any other post here, only a personal opinion

 

[steve_cronin]

Re: Drop whatever you are doing!

My anode can "see" all the seacocks as they are all on the same side and not too far away. If you've had a case of bad de-zincification as I did on a boat (P bracket & two mixed metal seacocks) then a bonding system is a wise precaution. On my last boat, after fitting the bonding (much liked by the eventual buyer's surveyor incidentally) all the fittings stayed corrosion free.

Since with the current (no pun intended) boat we have a possibility of all sorts of current leakage the bonding, including to the ground plate was considered essential.

I certainly don't like this "rather unusual" connection to the saildrive mentioned in the original post though.


One interesting point. My anode wasn't connected in straight away as I had to fly home and ran out of time but when it was connected, errosion was evident in a colour change within a few days so it must now be doing something.

The credentials of those suggesting that bonding isn't necessary are impeccable, I have no doubt, but with all the stray electricity around our boat a few pounds overespent isn't begrudged.

Steve Cronin



<hr width=100% size=1>The above is, like any other post here, only a personal opinion

 

[MainlySteam]

Re: Drop whatever you are doing!

I think we are pretty much in agreement regarding care with saildrives.

But with respect to your comment erosion was evident in a colour change within a few days so it must now be doing something I will repeat again that just because an anode is eroding does not mean that it is protecting anything. An experiment for demonstrating that is putting a bar of copper into the sea and the rate of erosion from corrosion will be essentially nil. If one then bolts a zinc anode to it the rate of erosion of the copper will be essentially unchanged but the zinc anode will erode, probably very quickly, even though it is not protecting anything. Of course, all one has done by providing unecessary zinc is create a shorted battery with consequent current flow which was not there before, and the need to replace a rapidly eroding anode.

John

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[steve_cronin]

Re: Drop whatever you are doing!

I can only go by my own experience John and again it's a case of better safe than sorry when you don't know what stray currents there are in a marina 1500 miles away.

As to your example of a simple cell, of course pure copper won't need protection in salt water. That is the point. unprotected brass will de-zincify and all you're left with is copper. I have no fears of my groundplate (sintered copper) dis-appearing in my lifetime nor the "Copperbot" company receiving many complaints that their bottom systems have vanished.

Steve Cronin



<hr width=100% size=1>The above is, like any other post here, only a personal opinion

 

[webcraft]

This is even more of a black art than radar, isn't it?

- Nick



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[hairbox]

Thank you everyone for your comments

I have spoken to an engineer at VOLSPEC, he has advised that providing there is no continuity between the battery negative and the bonding system it is ok to include the gearbox in the bonding system, it will in fact provide more protection to the saildrive/prop if a problem does develop. As far as the galley seacocks goes, they were possibly not included in the bonding system as they are above the waterline, to me the seacocks in the heads also appear to above the waterline.

I am having the boat lifted next week so providing all looks ok I will stick with it

This subject is certainly open to a lot of anomalies, I just pray all's ok THANKS

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[Guest]

Post deleted by danfoley

 

[Twister_Ken]

Doing a Jimi, no brown stains

Maybe there's a pregnant holding tank just waiting...

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[MainlySteam]

Is not a BlacK Art

No, it is not a black art at all but is in fact a very well understood one.

So well understood in fact that in the shipyards and with the naval architects I deal with (they are ones large enough to employ their own professional electrical engineers specialising in ship work) protection of the vessels being built from galvanic corrosion is hardly ever a topic of discussion as everyone has exactly the same view and it is just done correctly as a matter of course - and that is usually with aluminium vessels which require more care than plastic ones.

Where you find differences of opinion is outside of that professional environment because of misunderstanding and myth surrounding the fundamentals. Those misunderstandings extend into the pleasure market boatyards and electrical technicians (and surveyors too).

A very common misconception is that it is often the marina's fault when corrosion/erosion occurs - in fact it almost always is not (nice to blame the other guy syndrome). It is true that even when a boat is isolated from shore power it can be subject to electrical fields in the water itself, and they may cause problems. However, what most do not care to know is that these fields, should they exist, are only a problem with plastic boats if the boat is bonded (eg the field shortcuts through the low resistance path via a for'ard thru hull into the low resistance bonding system and out though the bonded shaft and propeller). The same plastic boatowners who are happy to blame marinas, are then perfectly happy to bond everything that previously was isolated and did not need to be bonded, together to zinc which creates a battery having the very same result as the marina field in the water example ie a current flows through the bonding system and through the surrounding sea. The more zinc put on the bigger will be that current (assuming there is enough cathode area (eg propellor, inside of ones engine/heat exchanger) exposed to the sea to support the bigger battery created.

It is a while since I read it but The 12 Volt Doctor's Practical Handbook, of which there are links to in other current threads, has a very good section on galvanic corrosion and while that internet version is early 1980's, nothing much has changed in the laws of physics since then. I think the only thing it is weak on (working from memory) is the coverage of alloys which may fail in seawater even if not connected to other metals (eg dezincification of some, but not all, brasses) - I do not think it points out that the key to that is material selection and correct electrical systems, not protection; protection is only a bandaid for such issues and failure of the protection (bonding conductor going high resistance, anode depleted, etc) will lead to heartache.

Sorry about the rant /forums/images/icons/crazy.gif, but I have to say that I am never surprised when pleasure boat owners have serious problems with galvanic/electrolytic corrosion issues on their boats.

John

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