Anodes

[Guest]

Does an anode have to be in contact with the cathode that it is protecting ?

Either say on a propshaft or connected by wire ?

Four years ago when I bought my current boat the survey stated that an anode should be placed near the bottom of the rudder to protect a bronze heel fitting as there were signs of wastage. I have never done anything about this as it is very difficult to make a bonding between the two. Also, to my untrained eye there appears to be no wastage or pinky colour. To add cofusion, I have read that as long as anodes can 'see' the cathode it will work.

Many Thanks

 

[Guest]

It will still do the job but to a lesser degree.
I would bond every thing to either the hull if it's steel or the bolt that holds the anode to the hull .
My tug which is 26 ft long and has 6 anodes fitted ,this was as per the recommendation of MG DUFF
I got the anodes I got from AH Latham marine who were very competitive on price.
They import the anodes from Canada the company is called
Martyr you can get them on the net
You can get shaft anodes even propeller nut anodes
There is a testing unit which tests the amount of corrosion present around the hull,but I expect it costs quite a bit

Mick

 

[Guest]

It is best to have the zinc (anode) in direct contact with the item it is intended to protect. Most often the anode will be connected via the bolt that passes through into the item it is to protect. More often than not shaft zincs have to be mounted then struck with a hammer in a particular spot so that a "copper bb" or ball is forced into contact with the shaft and zinc simultaneously.

If you cannot mount it directly to the item...make certain that they are connect with stainless wire or cable.

 

[VMALLOWS]

A lump of zinc (magnesium etc) connected to NOTHING? I don't think so. You are trying to create an electro-chemical cell so that the anode (zinc etc) wastes away rather than the more noble metal you want to protect. To create the cell there must be an electrical circuit between the two. (you can break the circuit and measure the current if you want to prove it's working.... of course you must be in the water).

An anode bolted directly to the item it protects is of course very well connected to the item it protects.

 

[BrianJ]

Vic...is your boat steel. ? If so then weld the bolts to the hull then slide the new anodes over the bolts (clean without any anti foul paint on them. Tighten the nuts and away you go.
BrianJ

 

[Mr Cassandra]

Hi Can you tell me if it is possble to fit to many , or too large an Anode. To a GRP Yacht And insted of the internal pencil type in the engin of a fresh water cooling system Could you not fit an external large anode on the block and wire it to the raw water seacock intake making a circuit Thanks Bob T

Bob T

 

[BrianJ]

Basically the answer is YES ...you can have too large an anode or too little.
I had a 36'steel yacht so really only know about steel.. we regularly tested the anodes and kept a log on their wear and tear. Hopefully someone who has more knowledge on GRP wi;; give you the answer you want.
Happy sailing
Brian

 

[VMALLOWS]

Please explain your reasoning that you can have too much/many anode(s)????... other than you are wasting your money, that is.

 

[Guest]

Actually....you really can't have too much "anode". You can place an oversized anode on a fitting, and the net resul is that you will just have a longer protective period. There are some examples of when and where an oversized anode can cause problems, but more often tha not it will involve a powerboat not a sailboat.

Generally when we are at anchor we connect a "zinc guppy" to the engine frame or drive shaft to give the running gear more
protection. Underway it is hauled in and disconnected. This zinc guppy weighs about 8 pounds and will last quite awhile.

I would be less concerned with "overprotecting" the boat than "underprotecting" it.

 

[johnlilley]

Just a minor point...be extremely careful about fitting and wiring anodes to timber vessels, as the electrical action encouraged by the anode can often destroy the timber surounding both the anode and the metal that the anode is meant to protect. eg the stern tube in many timber vessels when wired directly to the anode. A common sign of this type of destruction will be *furring* of the timber intrenally around the anode and the protected item. Also be aware of adding too many anodes on timber. Better to replace props occasionally than deadwood and other structure.....
John Lilley

John Lilley, John Lilley & Associates, Web site www.turbolink.co.uk navigate to survey page.

 

[Mr Cassandra]

Thanks John can you tell me if fitting to large or many to a grp boat maks any diffrence cheers bob t

Bob T

 

[johnlilley]

Hi
probably not, however it is easy to start new circuits by adding and wiring too many anodes that were not present before so unless you have an unusually active electrical installation and many mixed metal underwater fittings limit the amount by careful positioning of one or two...But ensure any electrical connections between metal & anode are failsafe. It has been known for a bronze P bracket to corrode severely simply because the wire connected to the bracket had simply been pushed into the casting, electrically failing almost from new.
John Lilley

John Lilley, John Lilley & Associates, Web site www.turbolink.co.uk navigate to survey page.

 

[Guest]

Thanks for the interest Brian !

In answer to you're question the boat's GRP.

Will take on board the advice about tightening my nuts but a current cold spell is taking care of that at present.

I notice that you are slumming it at around 30c at the moment in Oz and we pass on our sympathy towards you for having to put up with it.

Regards,

Vic

 

[BrianJ]

Sorry I wanted to wait for an "expert" (a scientist) to come back from the beach (its summer here) and give me the correct answer to "why". Here is his answer.
If the vessel has a good quality paint job below water line, then the amount/number of anodes will be minimal (disregarding props, prop shafts, rudders etc. that will require their owns anodes). The recommended quantities/number and their locations can be calculated based on surface area to be protected (ref. Metal Corrosion in Boats by Nigel Warren, Ch 9, pp 121-138 etc.) and boat design. Excess anodes will be a waste, but should not cause any other problems as far as I know.
Consider this: If the paint job was perfect and there is no exposed steel, then anodes would not be required. In the real world however, there are always imperfections and paint damage does occur - hence the need for anodes. If the exposed steel area is very small, one could argue that even a single anode would be excessive.
Note: If for any reason, surface voltages greater than those impressed on the hull by the corroding zinc anode occur, then other effects such as alkaline degradation of the paint may occur at cathodic areas. This will be found for example if one uses magnesium in place of zinc as an anode material, or maybe if there are leaky electric's in the boats electrical system etc.
In any case the steel will always be protected

Brian