anodes + rusty nuts !

[hamishb]

I am confused why the hull anode nuts and bolts ( which I thought were stainless ? ) always end up looking like rusty iron. I thought that the lead was supposed to sacrificially protect ALL metal parts it was in connection with ? I have tried to wire brush but the threads of the bolts look quite eroded. I usually change the anode every year ( the nuts are the real McCoy from the chandlers ) but I am economising this year as there is still a fair bit of lead left and I am concerned that I may have to change the hull bolts if I try to remove the rusty nuts.............. but I will only have the problem next year.
Anybody got the explanation ?

 

[Guest]

WOW!! No wonder you are confused!!

Couple of points:

1. The nuts that hold the anode in place will not get any "special protection" so if they are corroding - then so is everything else.

2. Note the term "corroding" rather than "eroding". "Erosion" is the physical removal of something by mechanical means (i.e. something is being "rubbed away") in the case of "corrosion" metal is being lost by chemical means.

3. If the bolts "look corroded" then they most probably are corroded. This probably means that they were somehow not in direct metal-to-metal contact with the anode.

4. The "lead" anode you refer to is (normally) a zinc/magnesium alloy. If you really have fitted "lead" then this explains everything as lead is one of the least active metals (almost the next one down the chain that goes platinum, gold, silver ........) and therefore offers zero protection so you MUST remove it!!

5. With regard to the rusty nuts - spray liberally with WD40 or something similar and wait patiently (with the odd re-spray) for a couple of days before trying to remove them. If the bolts are up to the job (i.e. will last another year) then use them - but protect them first with a hefty application of grease as you fit the nut and then wipe off and apply an overcoating of bitumen paint or something similar - and make sure that they retain metal-to-metal contact with the anode.

Hope this helps )

IanD

 

[Shanty]

If you bought the bolts & nuts that chandlers sell alongside anodes (metal rod with thread at both ends, and a square washer welded on part way along), these are normally mild steel - even though they look nice & shiny on the chandler's shelf. Thus, when you put them in the water, they will rust. Protect them with grease, tar, paint or whatever if you want to reuse them. Whatever you do, don't get any of the protective coating on the anode though, or you will reduce its effectiveness.

As Ian has remarked, anodes aren't made of lead. For seawater, they are made of zinc (which looks a bit like lead & is fairly dense). For fresh water, a magnesium alloy is used.

The zinc (or magnesium) protects any metal components to which it is bonded against galvanic corrosion - by corroding itself in preference to other metals. This protection depends on good electrical bonding between the anode, and the metal components being protected. A layer of rust will prevent good bonding, so make sure you clean the contact areas back to bright metal before fitting a new anode.

 

[Trevor_swfyc]

Firstly excellent replies cannot add much but I wonder if you are on a drying mooring and the rusting which is different from Galvanic corrossion is taking place when the boat dries out?
I protect the thread of the bolt with grease and then turn a short length of plastic pipe onto the thread, then cut of any excess pipe. Plastic pipe is easy to remove and underneath perfectly clean thread.
All the best
Trevor

 

[hamishb]

Thanks for all the tips.
My anodes are of course zinc ( I don't know where I got "lead" from ? ). I am sure that there is metal to metal contact between the zinc and the nuts as they are tight onto the anode plate. Is mild steel the best metal for the nuts / bolts ? ie why are they not stainless ? Would this results in other problems ?

 

[longjohnsilver]

Dont be tempted to mix the mild steel studs with stainless nuts, I did and found a few weeks ago the stud had disappeared!!

 

[ChrisP]

Painting the nuts and threads with dipit and whipit will protect the thread etc and can be pealed off next year to reveal shiny nuts and threads.

 

[JerryHawkins]

Get stainless studs

MG Duff produce stainless anode studs as replacements for their mild steel ones. I had to replace mine last year and I didn't want to do it again in a hurry so I got (had to order) some stainless ones, expensive, but worth it as getting the old mild steel ones out involved using an angle grinder and some "crispy" GRP hull!

Regards,

Jerry

 

[romany123]

Re: Get stainless studs

Had to drill my buggers out last week as they were so badly corroded, using a cobolt drill bit did the trick quite easily. Expensive nuts and bolts throught £4.65 for a bolt, nuts and electrical conector...still thats sailing


Dave