Clifford_Pope
regular
Reged: 28/10/2005
Posts: 716
Loc: Pembrokeshire
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My boat has survived 120 years with just traditional annual doses of hot tar on the bottom, but no protection against electroytic corrosion whatsoever. The planking is probably 80% original.
I have been told I ought to fit zinc anodes to everything in sight. I have also read that with a wooden boat it is very easy to overdo the "protection", and instead cause electrolitic decay of the wood itself around fastenings.
I half understand the theory of different metals having different electro-potentials, so one preferentially corroding, hence the positioning of sacrificial anodes. But surely that can happen only if the components are joined, so completing a circuit? Do two isolated items (eg iron keel, copper nails, bronze skin fitting) react in this way, or only if they touch or are linked (eg steel shaft, bronze propellor)
Do I need to do anything? Is it possible to measure the potential between fittings to determine how much protection might be needed? How do I avoid giving too much? Is there a simple guide anyone can recommend?
Thanks for any advice.
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mickshep
regular
Reged: 09/01/2003
Posts: 844
Loc: England
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When I bought my old 5 tonner, (Teak) She had survived 40 odd years with no anodes at all. thr prev' owner was advised to fit 2. 10yrs after fitting she required new timber scarfing into the area where the anodes fitted, the decay was on the inside of the hull where salt like deposits had built up around the anode fixings. I'm no expert but got rid of them, boat still floating and looking good. (Copper fastened with bronze shaft and prop). Mike.
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When I bought wood, they said, 'You'll be forever doing maintainance,' So I bought steel, They said 'You'll be forever doing maintainance' Now I've bought GRP, And all I'm ever doing is bloody maintainance!!(MUST BE A CLASSIC YACHT!!!!)
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Chrusty1
regular
Reged: 27/02/2008
Posts: 847
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Clifford???..........120 years, no anodes.....telling you something?? 
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Peterduck
regular
Reged: 10/04/2002
Posts: 994
Loc: Melbourne, Australia
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What's that old saying "If it ain't broke, don't fix it"?
My old ketch when I bought her, had two anodes which were not connected to anything. The frames on the inside of the boat at those points were so degraded with alkaline salts that I washed them away with a garden hose while trying to flush out the bilge.
Peter.
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Chrusty1
regular
Reged: 27/02/2008
Posts: 847
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"What's that old saying "If it ain't broke, don't fix it"?
Absolutely! You listening Cliffy babes? 
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Les_W
regular
Reged: 06/07/2007
Posts: 83
Loc: North Herts, boat in Essex
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Now you've got me interested!
Restoring a nearly 100 year old gaff yawl - Pitch Pine on Elm.
I've recently stripped the hull and raked all the seams. 99% of the planking is original. The only bit of planking that I've got to replace is where an anode was bolted through and connected to the engine - the wood's gone to a fibrous mush where the lignin's been destroyed. The boat has always had an engine and so it obviously has a shaft and prop (no anode was fitted when I got her), cast iron keel, usual metally skin fittings. Do you guys think I need to replace the hull anode or just put one on the prop shaft?
Sorry Clifford, I don't mean to muscle in!
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FlorealIII
regular
Reged: 22/01/2008
Posts: 72
Loc: antwerp
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The two different metals have to be linked to cause electrlolytic decay , because the electrons have to run from one metal to the other .
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Clifford_Pope
regular
Reged: 28/10/2005
Posts: 716
Loc: Pembrokeshire
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That's what I would have thought. But to read all the statements floating around, mostly from people who want to sell a set of anodes, all fittings should deliberately be linked with wire and then connected to the anode. In my ignorance that seems to me to be creating the very circumstances that we are trying to avoid.
My instinct is always to leave things alone if they are working, but I started to get worried after someone who appears to know (don't they all!) assured me I did need anodes.
I'm reassured to hear I am not alone. That's one job I don't need to add to my list.
Thanks everyone.
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meldrum
regular
Reged: 01/05/2008
Posts: 42
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This is a very interesting question as when I bought my boat, a 44 year old wooden water witch she had i 2 circular anodes bolted to the rudder either side a circular anode bolted to each bilge keel and that was it they werent bonded and there was no sign of electrolysis. however after reading various publications on electrolysis. and realising she was what was termed a llyods class 1 installation. (that is awooden boat with single engine and prop and mild steel rudder fittings) I then fitted anodes according to the reccommendations. that is one exterior long anode fitted midway between the gearbox and the stuffing box and bonded to the shaft and engine. As a consequence the original anodes still havent eroded atall the new one has almost dissappeared and the engine, seacocks prop and the various fasteneings around the boat have started to show alarming signs of electrolysis that were absent before I fitted and bonded this new anode. Go figure as the yanks say. I wouldnt bother if you dont have an existing problem.
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Tranona
regular
Reged: 10/11/2007
Posts: 1078
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Electrolysis occurs when two dissimilar metals are in an electrolyte - which in our case is seawater. They do not have to touch. Can be made worse when there is lots of electricity around such as the electric circuits in the boat, or in a marina when boats are connected to shorepower. Most older wooden boats did not have anodes because they generally had compatible metals, very little electrics and were on swinging moorings. Good time to stop and refer you to the experts www.mgduff.co.uk
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