Electro-confusion

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Previous engine installation had a big fat anode on the hull wired to the engine and also to all the seacocks (wired in series, not paralell)

With the new engine, Beta provide an anode actually on the engine and the flexible coupling means I also need a propshaft anode.

Or . . . rather than a shaft anode can I just wire across the centaflex coupling?

Do I still need the hull anode? If so, should the engine be connected to it as well as the seacocks, or just the seacocks?

If the engine has its own anode plus is wired to a hull anode will one disappear before the other or what?

Many peeps say wiring the seacocks isn't necessary . . . many peeps do it though. Can anyone explain why seacocks should be wired to an anode or alternatively tell me why they shouldn't? Is it more important if you spend time in marinas / on shorepower?

(That'll do for now . . .)
 
Re: OK, I\'ve done a search . . .

And it would appear that to earth or not earth seacocks is a point of endless debate, so lets' not open that can again.

However - I would like to know if it is a good idea to continue toconnect the engine to a hull anode when a dedicated engine anode is fitted . . .??

- Nick
 
Re: OK, I\'ve done a search . . .

IMHO the hull anode should be connected to the prop as before. As I understand it the hull anode is there to protect external metal fittings and must be connected to them.

I would connect to the engine also, though I must admit I don't really understand why they put anodes on the engine itself (for an anode to do it's job it must be connected to the item it is protecting but also in contact with the seawater). I suppose they protect the engine is it is sitting in a pool of bilge water?

A
 
Re: OK, I\'ve done a search . . .

Even if you connect the engine to an outside hull anode, it will not replace the effect an internal engine anode has, provided the engine anodes are correctly placed in the engine! It would almost be like reve /forums/images/graemlins/confused.gifrsing the question: Would You replace the outside anode with the engine anode?.
 
Bonding an engine.

Bit pointless IMHO. The path of the electrons through the water to make a circuit is beyond that which they will be bothered to take.

I would suggest a hull anode to protect (and therefore close to) a bronze p-bracket.

A shaft anode (if room to fit) to protect shaft and prop.

Intrnal engine anode is best to deal with that.

Sea cocks etc. remain open to debate, and on mine, remain open circuit.
 
The anode fitted to the Betas in the heat exchanger housing is intended to protect the saltwater side of the heat exchanger including the tubes. The engine itself is fresh water cooled and should have antifreeze (50%) with corrosion inhibitors as the coolant so no need for anodes in that circuit (think of a car engine - no anodes needed).

The setup I had on my previous Beta engined boat was such that I had the "big pear drop" shaped anode fitted externally on the hull which was connected internally to the engine block and to the "P" bracket and to the keel bolts. The drive shaft flexi coupling had a jumper lead fitted across it to give electrical continuity between the engine/gearbox/coupling/propshaft. In addition there was a shaft anode on the shaft (on the wet side of the stern gland) between the stern gland and the "P" bracket.

None of the sea cocks were connected.

I have a similar setup on my present boat except I have rigid drive so no flexi coupling to jumper. There were no signs of detrimental corrosion on any of the sea cocks (original Blakes)

Contrary to popular belief, the item being protected does not <u>need</u> to "see" the anode but must be connected to it by both the electrolyte (sea water in this case) and a physical electrical connection (bolted or by means of a conductor such as electrical cable).

As the anode in the heat exchanger can be easily changed without draining the system it is worth removing it fairly frequently to check the condition, at least until you establish the frequency of changing. I only had to change mine about every 18 months whereas another beta owner berthed near me had to change his anode twice a season - the only difference we could see was he did not have an external anode connected to the engine.
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"Artificial intelligence is no match for natural stupidity"
 
"Contrary to popular belief, the item being protected does not need to "see" the anode but must be connected to it by both the electrolyte (sea water in this case) and a physical electrical connection (bolted or by means of a conductor such as electrical cable)."

Absolutely not true. Every known authority will insist that the object being protected and the anode must be in line of sight. Thus protecting an engine with a hull anode is not possible, disregarding the fact that there is no continuity through the water pump.

So far as the original question is concerned, a shaft anode is undoubtedly the only one that is essential. Arguments continue regarding any others, although it seems to me that in purely galvanic situations there is no need in the majority of cases, whereas if electrolytic corrosion is a problem (impressed current, stray currents, etc) there is probably justification for specific cases.
 
As I understand it, the anode in the engine is to protect the heat exchanger. It's common marine practice to have an anode in heat exchangers.

In my own case, I also have a Beta with an anode in the heat exchanger, hull anode connected to engine along with battery negative. The shore power goes through a galvanic isolator to the engine. The battery charger and 240v shorepower socket earths are also connected to the engine. No earths on the sea cocks.

It seems to work O.K. so I'm not changing anything.
 
Read what I said carefully.
The anode does NOT have to be in line of sight to the surface/item being protected.
Certainly the closer the two are the more efficient the protection possible.

Interesting thought though, consider your prop shaft - sections of that will not be in line of sight even a shaft anode if one has a "P" bracket.
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"Artificial intelligence is no match for natural stupidity"
 
I did read it carefully. I don't know where you obtained your information but no authority that I am aware of would support it. The P-bracket statement is a red herring - the P-bracket is not protected by a shaft anode as there is no electrical connection through the cutless bearing. OK, I am well aware that some carbon filled rubbers are conducting (eg tyres) but I have no idea whether cutless rubber bearings are. I would certainly not rely on this possibility. The prop and shaft are protected because there is a direct connection between them and the anode.

The reality is that a P-bracket is normally made from a metal that is, for most practical purposes, resistant to corrosion by seawater. ( I recently removed mine and cut it open to check. After 20 years of use there is negligible dezincification, without an anode.) Coating it with epoxy will preserve it more effectively than the hit-or-miss action of an anode placed somewhere on the hull. Where there are stray currents about almost anything may happen, hence the wording of my earlier post.
 
I think you should have your sources explain to you the difference in "seeing" as in line of sight" and "seeing" as in electrolytically in relation to anodic protection systems, it might then be claer to you that line of sight is NOT required and this comes from years working in the fields of metallurgy and corrosion protection systems.
EOD
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"Artificial intelligence is no match for natural stupidity"
 
The verb "to see" is clearly more complex than I understood.

The MG Duff website clearly says under fitting, main points to remember 'The anodes can “see” the parts to be protected'. Nigel Warren, writing in PBO April 2006 says' An anode basically will only protect something if it can 'see' it and the distance away is not too great. The protective current will not go around corners...'

I'm afraid I cannot see the difference between 'see' and 'line of sight' in the context of these definitions. Neither pretends to be highly technical and use of the word appears to be unequivocal.
 
[ QUOTE ]
The protective current will not go around corners...

[/ QUOTE ]That is where the problem lies as the current WILL go round corners. For an anode to see the cathode it must be in reasonable proximity to the cathode (the bit being protected).

Just had a word with a nice gentleman in MG Duff Technical dept to clarify the term "see" seems they use it to assist the average boat owner in understanding where to place an anode for good performance. Once I explained to him I was a Metallurgist with many years in the field he immediately reverted to the technicalities rather than layman's terms and confirmed the anode does not have to be in line of sight but for good performance must be connected electrically and electrolytically but this concept was generally to confusing for the average boat owner.

A really interesting chap and certainly came over as well versed in the subject.

Definitely EOD.
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"Artificial intelligence is no match for natural stupidity"
 
I believe that you are essentially correct vyv_cox.

Where many go wrong when thinking about the current flow and voltage between an anode and a cathode through the sea is they imagine it as like current flowing in a piece of wire. But that is not so as a piece of wire is bounded it being a piece of isolated conductor of long length and very small diameter (that is very small in comparison to length).

In the case of an anode and cathode in the sea, say, the electric field is not bounded but forms in 3 dimensions in the sea between and about the path between the cathode and anode and the intensity of that field varies according to where you measure it. If any less conducting object is placed between them then the field is both distorted and the field paths lengthened.

It has been a long time since I have done this but I assume that the physics has not changed. Get a plastic tray (must be an insulting material), fill it with moist sand and place a piece of metal one at each end of the tray in the sand to use as terminals (not as cathode and anode). Connect a reasonable voltage battery to the to the two terminals, +ve to one and -ve to the other then using the probes of a multimeter set to volts explore the voltage differences in the sand across various parts of it. In places you find that you get a high voltage and in others a very low or maybe no voltage at all. It is the voltage differences in the voltage field between the two metal terminals that you are measuring.

Then screen off part of the sand with a piece of plastic or similar so that the terminals cannot "see" each other (that is placed vertically in the sand at say 90 degrees across the path between the two terminals) and you will find that the field has been greatly distorted. This is the same effect as with an anode and cathode in salt water that do not "see" each other - the field becomes both distorted around the insulator and the path lengths longer.

The term "see" is a simplistic one but the essential concern is to maintain as "strong" a field as possible between the anode and the metal it is protecting. Putting aside the differing galvanic status of the anode and cathode the obvious influences on the field are both their distance apart and the directness of the 3 dimensional space (the seawater) that the field can form in.

So, in a plastic boat, for example, one has a different circumstance on the air side of the cell compared to the sea side. On the air side one has the bonding wire of low resistance material which can essentially run all around the boat and be as long as you like but the only effect on the cathodic protection is the increasing resistance of the wire as it gets longer (but, of course, is of no effect in small boat type lengths of wire). But on the sea side one does not have a piece of wire but a 3 dimensional volume of not so good conducting sea water in which the electric field between the anode and cathode forms in. Anything placed between the anode and cathode will distort the field and if an insulator will increase the distance the lines of force have to travel. If the sea was as conductive as copper then it would not matter, but it is not and for such protection in the ground (say pipelines) obviously it is less conductive again.

I deal mainly with aluminium boats and it is the case with them that the anodes are distributed around them in order to maintain such fields and that means in the simple sense that they can "see" the metal they are protecting. For example the hull will be protected by distributed anodes but others will be placed in the sea chest even if the whole of the bottom of the sea chest is open to the sea so a conductive path exists into it. It is along time since I project managed petroleum pipeline projects (1980's) but I do recall that similar concerns applied then and due to the same physics and the low conductivity of the ground I assume the same concerns still apply.

Hopefully no one will drive me to swotting up field theory again - I found the maths of curl, divergence etc pretty tedious and that was a more than a goodly few years ago now and so will only have got worse /forums/images/graemlins/smile.gif.

John
 
I'm with Cliff on this. It is within his field of expertise and he has taken the trouble to talk to the technical department at MG Duff.

What is important is the path length between the anode and the protected item. OK putting some obstruction between them will increase the path length if it is a large obstruction but a small one, just large enough to block the line of sight, will not have a significant effect.

Aluminium boats are a special case because a high level of protection must be maintained equally over the entire hull. Also because the surface area being protected is so large a large total anode surface area is necessary to prevent frequent anode replacement and other unwanted effects caused by high current densities at the anodes. Using a large number of anodes distributed around the hull will satisfy both of these requirements.
 
'If the sea was as conductive as copper then it would not matter, but it is not and for such protection in the ground (say pipelines) obviously it is less conductive again.'

I think that this is where the confusion lies. Many people seem to think that seawater conducts almost as well as a copper wire does. Unfortunately it does not.
 
When a galvanic couple forms, one of the metals in the couple becomes the anode and corrodes faster than it would all by itself, while the other becomes the cathode and corrodes slower than it would alone. For galvanic corrosion to occur, three conditions must be present:

1) Electrochemically dissimilar metals must be present;

2) These metals must be in electrical contact (e.g. electrically bonded or jumpered); and

3) The metals must be exposed to an electrolyte. (e.g. sea water)

The principle was also engineered into the useful protection of metallic structures by Sir Humphry Davy and Michael Faraday in the early part of the nineteenth century. The sacrificial corrosion of one metal such as zinc, magnesium or aluminum is a widespread method of cathodically protecting metallic structures.

The relative nobility of a material can be predicted by measuring its corrosion potential. The well known galvanic series lists the relative nobility of certain materials in sea water. A small anode/cathode area ratio is highly undesirable. In this case, the galvanic current is concentrated onto a small anodic area. Rapid thickness loss of the dissolving anode tends to occur under these conditions. Galvanic corrosion problems should be solved by designing to avoid these problems in the first place.

There has been some confusion regarding oxidation-reduction electromotive-force potentials and the galvanic series. While there are similarities between the galvanic series and standard reduction potentials, there are also some fundamental differences. While standard potentials can provide an indication of the stability of a metal, as it is done with E-pH or Pourbaix diagrams, galvanic series are used to predict whether or not galvanic corrosion will occur, and if so, which of the two coupled metals will exhibit increased corrosion. Thus, these two tabulations have entirely different uses and should therefore not be confused.

As a demonstration one can setup a galvanic sell in a large beaker or non conductive tank. bringing the anode and cathode closer will increase the current flow (protection).
Placing a non conductive barrier between the anode and cathode will reduce the current slightly but not stop it provided there is a path through the electrolyte. The above is a simple demonstration / experiment carried out in science classes in secondary / high schools to demonstrate a few basic principles of the electrochemical series / galvanic cells/couples and cathodic protection (sacrificial the anode) to science students in schools
QED & EOD.
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"Artificial intelligence is no match for natural stupidity"
 
Well despite the assumptions of some this is a field that I too work in, directly with quality commercial vessels.

A simple example may show the point. Imagine a plastic boat with no keel, a seacock in port and starboard bilges both bonded together and to an anode on the starboard side. The starboard seacock is closer to the anode than the port seacock is.

Now, I think most would agree that the closer seacock is going to be better protected than the further away port one (if you don't agree with that then I have to give up on you /forums/images/graemlins/smile.gif - even Cliff with his beaker experiment says it is so). So then we now decide to put a big fin keel on the boat directly between the seacocks and between the anode and the port seacock. Now, again I think most will see that will greatly distort the field between the anode on the starboard side and the seacock on the port side - in effect making the "path" length greater.

I put "path" in inverted commas because we are not talking about a path as water flowing through a pipe or the approximation one can make to electricity flowing through a wire having a "path" - we are talking about a field which is 3 dimensional and covers a volume of the water (in fact, the modern physicists amongst us may argue that the volume that the field fills is infinite, but of course we normally only consider the close in circumstance).

Now my example with the bonded seacocks has a flaw because if I was specifying the boat the seacocks would be of a material suitable to the saltwater environment and would not be bonded and protected at all. But for the sake of an example I have ignored that.

Getting back to the "seeing" statement. I think that people who accept that we are dealing with fields here (and if you don't accept that then I suggest that you have a cruise on the internet as there are quite alot of technical papers investigating the field and the effect on it of the distribution of anodes and protuberances on vessels) will see that using the rule of anodes "seeing" the metal they protect has some merit even though we tend to think of seeing in terms of visible light and the vantage point of our eyes.

But in fact the term "seeing" is a physically correct statement in the context as physicists refer to all fields, regardless of their energy (eg including radio, microwave, etc and electric) as "light". Again for those doubters you may wish to do a little research on that and I have no doubt that you will find that it is so.

So, in our case in the sea with anodes and metals being protected the field, in general terms, to a physicist is "light" and its ability to be sensed, detected, interact between two things is "seeing".

As a close, I hope people can see that the situation of cathodically protecting a boat is quite different to comparison to a cell in a beaker or whatever in a lab, or even the micro and larger mechanisms that take place when two differing metals are in contact. Those are the things most corrosion engineers are familiar with. The boat situation is a macro one of a large irregularly shaped object floating in the sea and while the basic physics is the same the distribution of the field is quite different because of the size of the boat and all the other influences on it (such as the keel in the seacock example above). I tried to show that on a small scale with the sand in the tray experiment. Any doubters are welcome to try that - they will see that what I say is what they will see.

Again, if the sea was as conductive as copper then it would not much matter but it is not and so the "path" length between the anode and the metal being protected is important (I hope all agree with at least that bit else it would not matter much where we put our anodes). The "path" becomes longer if the anode cannot "see" the metal it is protecting because the field is distorted by the intervening object (eg the keel in the seacock example) and so that matters too; that even more especially so if the surrounding environment is not very conductive such as metals in the soil - I hope a few more can see that point now.

On past experience some (eg Cliff /forums/images/graemlins/smile.gif) will never be convinced and I give up on them. For those with more open minds and if interested, as I said there is quite alot of material on the internet dealing with vessels and the fields induced through protection - the maths in some of them is pretty advanced but some have pretty pictures modeling the fields.

John
 
It may also help those considering how "path" length of an electric field affects protection from an anode to remember that the voltage varies inversely as the distance ie double the distance and the voltage halves. But to also remember that the power density changes inversely as the SQUARE of the distance and indirectly this is the energy available to drive the protective cell (radio amateurs will be familiar with that concept through comparison with electric and magnetic fields around antennas). So the path length is far more important than just being a straight linear relationship such as for resistance in a piece of wire (eg resistance of wire doubles if length is doubled).

Note that I am not talking about the voltage measured at the terminals of the cell formed by the anode and the metal being protected but am referring to the voltage in the field on the seawater side and the energy available to drive the cell.

John
 
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