What metal to bolt on anode?

[Gerry]

Just changing our main boat anode for the first time in ten years!

Taking it off there is a mild steel bolt with a stainless nut. What should we use to replace this set up? We have stainless bolts of the right size but are they more likely to rust?

And would bronze be even better?

 

[VicS]

The usual fastenings are zinc plated steel. The anode protects them from corrosion!

Stainless fastenings are available if you like bright and shiny.

Dont use bronze. That will cause increased loss of zinc

They are special studs see http://www.mgduff.co.uk/mgduff-product-catalog/Ancillaries/Ancillary+Item+Studs/


See also http://www.mgduff.co.uk/leisure-craft/fitting-instructions/ for the fitting insructions.

Make sure there is good electrical bonding between the anode and the item(s) it is being fitted to protect

 

[Bloater]

I think anyone giving advice about anodes would tell you that 10 years is too long for an anode to last. It cannot be doing its job properly. You may well need to check all other metal surfaces as these could well have eroded in preference to your anode.

You will probably find that the bolts are in fact stainless, try checking them with a magnet (stainless is not magnetic). You should replace then with stainless bolts and these are sold as such specifically for mounting abodes.

 

[VicS]

I think anyone giving advice about anodes would tell you that 10 years is too long for an anode to last. It cannot be doing its job properly. You may well need to check all other metal surfaces as these could well have eroded in preference to your anode.

You will probably find that the bolts are in fact stainless, try checking them with a magnet (stainless is not magnetic). You should replace then with stainless bolts and these are sold as such specifically for mounting abodes.

Yes just revisited the thread to say that.

Check the bonding to whatever it is protecting.

It is possible the anode is totally unnecessary if there is no excessive corrosion of underwater bits and pieces.

What is it supposed to be protecting.

 

[Gerry]

We have a zinc on our prop. The anode is connected to the engine, a Perkins M50, which doesn't have any zinc for example in the heat exchanger and is potentially an isolated ground. But we are grounding it to the battery negative terminal and to the external anode, which may be excessive.

The boat is isolated from shore power by a 50 amp Victron isolation transformer and since there is no sign of erosion on the bronze thru hulls or on the heat exchanger tubes we tend to think that this set up is working.

The zinc that I have just removed was held in place by a mild steel stud with stainless steel nuts. We were told that stainless could be a problem at the point where it is excluded from oxygen because of the 5200/sikaflex sealant and also that stainless was a poor material for the stud because it doesn't conduct electricity very well. Needless to say the mild steel end of the stud which protrudes above the bilge does get salty water on it and has rusted!

So, should I use stainless, mild steel or galvanized mild steel for my nuts and bolts to hold the anode in place?

 

[vyv_cox]

We have a zinc on our prop. The anode is connected to the engine, a Perkins M50, which doesn't have any zinc for example in the heat exchanger and is potentially an isolated ground. But we are grounding it to the battery negative terminal and to the external anode, which may be excessive.

The boat is isolated from shore power by a 50 amp Victron isolation transformer and since there is no sign of erosion on the bronze thru hulls or on the heat exchanger tubes we tend to think that this set up is working.

The zinc that I have just removed was held in place by a mild steel stud with stainless steel nuts. We were told that stainless could be a problem at the point where it is excluded from oxygen because of the 5200/sikaflex sealant and also that stainless was a poor material for the stud because it doesn't conduct electricity very well. Needless to say the mild steel end of the stud which protrudes above the bilge does get salty water on it and has rusted!

So, should I use stainless, mild steel or galvanized mild steel for my nuts and bolts to hold the anode in place?

Engines cannot be protected by an external anode. Anodes need to 'see' the object they are protecting, as electrons travel in straight lines in seawater. Electrons do not dive up the seawater hose supply to the engine, so there is no possibility of a circuit. It is likely that your anode is doing nothing, other than gently corroding itself away.

As VicS has said, the anode protects the bolts from corrosion when they are immersed. This does not happen when the boat is out of the water, which is when they corrode. It is wise to clean up the bolts before launching to ensure good electrical conductivity. Mild steel bolts are generally sold for the purpose of holding anodes and stainless ones give no benefits. Even when ashore the stainless may not corrode but the strap cast into the anode, which is invariably mild steel, will.

 

[Tranona]

The only reason for bonding the anode to the engine is to provide a path to the stern gear, but this needs either to be through a solid coupling or bridged across a flexible coupling. if an engine needs protection it will have an anode in it, usually in the heat exchanger. Suspect your anode has lasted 10 years because it is not doing anything so you might just as well remove it and fill the holes. Presumably your prop anode is doing its job.

 

[VicS]

So, should I use stainless, mild steel or galvanized mild steel for my nuts and bolts to hold the anode in place?

Your choice I think. I'd use the zinc plated fastenings but if you want it to look all bright and shiny when its hauled out choose the stainless ones.

I expect the stainless ones will be even even more expensive than the zinc plated ones.
Note though that these are special studs not just ordinary bolts.
Id not mix stainless nuts with zinc plated studs, or vice versa, but the fastenings are supplied complete with the necessary nuts all in the same material.

As Vyv says an anode on the hull offers no protection to the engine cooling system.

With indirect cooling the engine itself is protected by the inhibitors in the antifreeze in the cooling circuit.

There may or may not be an anode in the salt water side of the heat exchanger. Refer to the users manual and if there is an anode ensure that it is renewed when necessary.

If your hull anode is fitted to give additional protection to the stern gear there must be a good electrical path between the two.
Normally this is achieved by bonding the anode to the engine or gearbox but if there is a flexible coupling in the shaft it must be bridged to complete the circuit.

If your engine has an isolated negative return, i.e. the block is not used as the negative connection, the anode can be simply connected to the block. There is no need to also ground the battery negative, it can remain isolated.

I suspect your anode has been doing nothing to have lasted 10 years. If the prop anode is adequately protecting the prop then the hull anode may well be completely unnecessary.

 

[Gerry]

Thank you so very much. I am beginning to get a much clearer understanding of a subject, which to say the least, is somewhat murky to me!

Yes we regularly renew the prop(maxprop) anode, it varies depending on whether we have been in a marina or not. Every 6-9 months at anchor and up to every 3 months in a marina, sometimes more!

I suspect that you are correct in saying that the anode is doing nothing except fizzing away quietly on it's own! As I already have a shiny new one ready to go I think I'll put it on anyway, sort of offering to the Gods of electricity............

Once again thanks to all, I am certainly often reminded by the boat of how much I don't know!

 

[VicS]

Thank you so very much. I am beginning to get a much clearer understanding of a subject, which to say the least, is somewhat murky to me!

Yes we regularly renew the prop(maxprop) anode, it varies depending on whether we have been in a marina or not. Every 6-9 months at anchor and up to every 3 months in a marina, sometimes more!

I suspect that you are correct in saying that the anode is doing nothing except fizzing away quietly on it's own! As I already have a shiny new one ready to go I think I'll put it on anyway, sort of offering to the Gods of electricity............

Once again thanks to all, I am certainly often reminded by the boat of how much I don't know!

I'd be wondering why the prop anode lasts for so little time in a marina compared with being on a mooring

You say you have an isolating transformer on the shorepower supply. I'd check that the incoming shorepower earth is not in fact connected to the boats internal earth or DC negative.


I also noticed an earlier mention of through hull fittings
Bronze ( or DZR) fittings should not be bonded to anything and being resistant to corrosion do not need the protection of an anode.

 

[Gerry]

Marinas have always been a little, shall we say, rough! Anode goes in these!

The bronze thru hulls are not connected and are all in fine fettle, I have just serviced the whole lot of them!

thanks for all the hints and tips...