Replacing anodes on a steel boat

[BigART]

We are replacing the anodes on our steel boat and I would like to use washers under the nuts for improved contact area and security. What is the best arrangement for the fixing? Can I use standard stainless steel washers or do I need to find some galvanised ones?

The hull is galvanised and coated with loads of epoxy/antifouling so no rust problems there. The anodes are Vetus types, about 12 cm long, 8 cm wide with two holes in the casting which fit onto studs welded onto the hull. The holes have steel plates embedded in them which contain the 'hole'.

 

[gus]

Doesn't matter whether you use stainless or galvanised or plain mild steel washers as the anode will protect them from corrosion. Test your 'connection' with a meter between the end of the stud and the anode.
Have you bought your anodes yet? I have a steel craft and I have found aluminium anodes to have been perfectly suitable for the past 10 years - replaced every 3 to 4 years when half eroded. I purchase them from Jotun at a small fraction of the price you would normally expect to pay. Usually about a sixth.
Here's to steel sailors!

Gus

 

[BigART]

Thanks for that. Glad to know the washers aren't fussy, I was just concerned that the SS might accelerate the erosion of the anodes.

Aluminium - never thought of that! Thought they were for freshwater or something.

Who wants to sail in a yoghurt pot.....

 

[richardandtracy]

I agree about the actual type of washer not being a concern, however I'd tend to avoid the MS washer - it'll just add an extra protection load on the anode. I'd go for galvanised or BZP (which tend to be cheaper in my stockist than the unplated ones).

As for using aluminium for the anode. It really depends on the alloy used. There are types of aluminium that are protected by steel.. (7075 is one). Be very careful! The best type to use are the wrought alloys (2000 or 6000 series) as they have the highest galvanic potential, but even so, thay have a voltage difference from steel of about 0.2V compared to 0.3V for zinc. Consequently you'll need more and have to be more careful to site them in the right places otherwise you risk not having adequate protection. Remember not to used anodized aluminium!

One other thing, the aluminium anodes will not give a great enough voltage difference to protect your boat in fresh water.

Regards,

Richard.

 

[AndrewB]

[ QUOTE ]
I'd tend to avoid the MS washer - it'll just add an extra protection load on the anode

[/ QUOTE ]Its so tiny surely it makes no difference! And a galvanised washer would quickly be dezinced. Incidentally, I usually add a blob of paint to protect my MS anode studs and washers after the anodes are fitted, but as long as they are a little way underwater rust isn't a major factor.

Agree with you that aluminium will offer weaker protection - particularly I suspect to an ali-bronze (AB2) propellor which a zinc anode will properly protect.

 

[gus]

"One other thing, the aluminium anodes will not give a great enough voltage difference to protect your boat in fresh water"

I usually thought that it was the other way about. However what anyone says - I have found it to work well for me which is what matters. I had exposed steel on side of the keel for 4 months this year and when she was lifted out it was amazing to see clean and completely rust free steel. As I said before the anodes are supplied by Jotun - as anodes and are a small fraction of the price of normal zinc anodes.

Gus

 

[poriordan]

Hello there BigArt !

Do not be too worried about what washers you put in for the anodes. Mild steel is ok with me, as the voltage difference is small but stainless is also ok as difference is hardly nothing.. Just make sure the earth continuity is alright from the bolt head / anode earth back to the battery earth. Hope you have a multimeter !