What is an anode?

millbeach

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As a novice yachtsman could any one explain to me the use of an ANODE?
I am aware that it made of lead.
Could you please post IE,what its function is.?
Where it is placed ?.
I have little info but need clarification.
Many thanks...:confused:
 

William_H

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Anode

No it is usually made of zinc but sometimes other metals.
Electrolytic corrosion comes from having different metals in an electrolyte (salt water) The metals make what is in effect a battery (electric cell) which generates a voltage between the 2 metals. If they are then electrically connected (which they usually are) then a current flows. Metal migrates from the least noble metal to the most noble.
The scale of noble metals lists metals essentially according to their chemical activity. So gold is chemically very inert and so most noble. Zinc Aluminium and the more unstable metals are the least noble.
A bronze propeller (or similar fitting) has a lot of zinc in with the copper. If this is fitted to a stainless steel shaft then the zinc will leach out of the bronze. (onto the SS) The loss of zinc makes the bronze eventually fall apart.
An anode is a piece of zinc which we can afford to sacrifice. It is almost like a bait or lure to take electrolysis away from the valuable propeller. Ideally the anode should be less noble than the protected material so that a potential difference (voltage) is set up in opposition to the original destructive current.

So an anode is used to protect susceptible underwater metal parts. It must be electrically connected to the part to be protected and be mounted (or hung) near the part to be protected. Typically a 200 gram lump of zinc might lose half its mass in one year. so must be checked replaced regularly.
Obviously boats with no metal underwater (outboard powered) or with just one metal do not need to have protection.
Just to confuse things it is possible for electrical supplies (marina power) to pass current into the water via your underwater metals. This current can massively accelerate it. (deplete anodes very quickly)
So it is a good idea to check your anodic protection system initially at least within a month or so. especially if you have just moved to a marina and use the power.
I am sure others will add more perhaps more accurate detail to this. Feel free olewill
 

Bajansailor

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The basic function of an anode is to protect other metals that are electrically connected to it. I dont know of any lead anodes - they would be rather heavy!

Anodes are usually made with zinc, and these work well for the average boat in salt water.
There are also aluminium and magnesium anodes for more specialised applications, such as use in fresh water.

In addition to being electrically connected to what they are protecting (eg a stern tube, or outdrive leg, or rudder), anodes should also ideally be able to 'see' the object(s) they are looking after - ie line of sight.

Lots of good info about anodes on the M G Duff website at http://www.mgduff.co.uk/
 

millbeach

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I am sure that i have no anode on my boat.
I have a bronze coloured prop, should i place an anode on my prop shaft?
And could i wait till October,when she is hauled out for winter?.
Thanks you...
 

Bajansailor

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If you had a hull anode, it would probably be a pear or lozenge shaped lump of zinc that is through bolted to the hull - there is then usually a copper strap or bonding wire going from the stud on the inside to the item(s) being protected.
If it is connected to the engine, and you have an insulated shaft coupling, then this would have to be bridged with a wire for the anode to protect the propeller.

Maybe your boat has only ever had a shaft anode, and the last one disappeared?
I see you have a Jeanneau 27 - fin keel or were they also built with lifting keels?
I suppose you can't dry it out very easily.
Have you got a pal with a keen interest in scuba diving who also likes sailing?
And some reasonably clear and clean water nearby?
It is possible to fit a shaft anode underwater - you just need the right sized allen key.
And a determination not to drop it, or the bits of the anode....... :)
 

millbeach

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Thanks for info.
On boat this weekend will check to see if i have any copper straping on prop shaft from engine.
Yes can beach boat at low tide, and fit anode direct to prop shaft.
Would this be a good idea till i haul out over winter?
By the way, having antifouled before launch i can not recaul any hull anodes on boat.
 

Bajansailor

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If you have an 'ordinary' steel shaft coupling (ie not an insulated one) then you will not need to have a bridging wire across the coupling.
If you havent got any anode on the propeller shaft now, and you have the ability to beach the boat fairly easily, I would want to fit a new shaft anode now, rather than waiting until October.
 

guernseyman

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As a novice yachtsman could any one explain to me the use of an ANODE?

Just looking at the terms of the question, it seems to me that millbeach may need to be advised that the anode should be connected to the positive side of the battery. On a boat the engine and connected components, which are the major ones to be protected, are usually connected to the positive terminal of the battery, and there is little chance of a mistake.

However, as one possibility, if millbeach's boat has been wired up by an automobile mechanic, then the connections may be the other way round. Then his zinc sacrificial anode would actually be a cathode, and not work to protect his under water metal parts.
 

VicS

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Will def fit zinc anode on prop shaft at earliest opp..
Why? Is there any evidence that you require one?

or are you just fixing something that isn't broken ?
 

Tranona

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Sir, many thanks.
Will def fit zinc anode on prop shaft at earliest opp..:)

Agree with Vic. If the boat does not have an anode then it probably does not need one! It is presumably not new, so if it needed one it would be fitted by now or the prop would have dezincified.

Sometimes it is necessary to fit one if a boat is moved to a different mooring, for example from a swinging mooring to a marina with lots of steel work and other boats around that set up stray electric currents. Don't worry about it unless you do already have one and it is worn away. If it is on the prop shaft make sure you accurately measure the diameter, particularly if it is 25mm or 1 inch as they are made exactly to size to get the proper electrical contact.
 

alahol2

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Just looking at the terms of the question, it seems to me that millbeach may need to be advised that the anode should be connected to the positive side of the battery. On a boat the engine and connected components, which are the major ones to be protected, are usually connected to the positive terminal of the battery, and there is little chance of a mistake.

However, as one possibility, if millbeach's boat has been wired up by an automobile mechanic, then the connections may be the other way round. Then his zinc sacrificial anode would actually be a cathode, and not work to protect his under water metal parts.

Maybe I've misunderstood what you are saying but an anode DEFINITELY shouldn't be connected directly to the battery. It is normally attached to the engine block and or shaft (and sometimes through hull fittings). The engine block is usually negative earth (in the UK anyway).
 

VicS

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Just looking at the terms of the question, it seems to me that millbeach may need to be advised that the anode should be connected to the positive side of the battery. On a boat the engine and connected components, which are the major ones to be protected, are usually connected to the positive terminal of the battery, and there is little chance of a mistake.

Most boats are negative earthed.

If you connect an anode to battery positive with a negative earthed system there will be a lot of fizzing, a noticeable smell of chlorine and the anode will disappear very quickly.
Once it has gone the electrolysis will then similarly attack the bolt to which the bonding wire is attached. When that has gone there will be a hole in the hull and the boat will sink!
 

Fantasie 19

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I've always wondered about anodes as well - so thanks for asking the question, and also the responses..

It leaves me one puzzle though - why is there an anode on the bottom of my outboard??? It's not electrically connected to anything? :confused:
 

VicS

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It leaves me one puzzle though - why is there an anode on the bottom of my outboard??? It's not electrically connected to anything?

To protect the outboard! The anode is connected to the outboard even if the outboard is not connected to anything else

likewise saildrives which are likely to be electrically isolated from everything else have anodes. Usually one on the leg itself to protect that and one on the prop to protect that.
 

Tranona

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I've always wondered about anodes as well - so thanks for asking the question, and also the responses..

It leaves me one puzzle though - why is there an anode on the bottom of my outboard??? It's not electrically connected to anything? :confused:

Outboards are a mix of metals, particularly Stainless Steel and Aluminium. These have different galvanic potential and seawater acts as an electrolite creating effectively a battery . Zinc is lower on the galvanic scale and will erode rather than your nice aluminium casing!

Once you have seen an outdrive/outboard/saildrive that has not had its anodes replaced you will be extra careful to do yours!
 

millbeach

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Well thanks gang for info.
My boat is a Jeanneau Fantasia, 27 ft, lift keel, 1984.
Bought it of a chap who had it from new.
When anti fouling in spring, noticed prop shaft was fully coated with anti foul.
My guess is that it has never had anode fitted to shaft.
He had boat on a swing mooring, as i do also.
Have 2 wing prop (bronze coloured) with looks in very good shape to be honest.
Must admit will probably beach boat later and fit anode to prop shaft, as i deem it can do no harm to do so.
Many thank chaps...
 

Pasarell

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Shaft anode

You will need to scrape the antifouling off the shaft before you fit the anode, at least in the area where you fit the anode. It must have direct electrical contact with the metal or it will have no effect
 

guernseyman

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Maybe I've misunderstood what you are saying but an anode DEFINITELY shouldn't be connected directly to the battery. It is normally attached to the engine block and or shaft (and sometimes through hull fittings). The engine block is usually negative earth (in the UK anyway).

You certainly did misunderstand. I would have hoped that the comments about the polarity of the engine block were clear enough.
 
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