 Using old anodes for extra protection is a good tip. However, I'm not sure the "hot metal" advice is such a good idea, and not only because of the proactical difficulty of home smelting!
I asked the engineer at our marina why old anodes weren't melted down for recycling (as newspaper type used to be, in the hot metal printing days).
He said it was because the proportions of metal in the mix were critical to the effectiveness of the anodes, and reheating them would alter the characteristics which make them work.
I'm not sure whether this is sound metallurgy, or just an excuse to make us buy more new ones from him. Can anybody tell me?
In the meantime, Richard is right. It makes far more sense to "use up" last year's anodes by hanging them over the side than to buy yet more, designed for the task.
In our marina, metal piles add to the "battery effect" and it's a case of: the more anodes the better.
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02/06/08 12:29
 Hi Cathy I've metled plenty of scrap lead in my time to make weights for fishing but I'm not sure of the melting point of the materials involved so it may be a lot more difficult. As far as the metallurgy is concerned; if anodes are made from a zinc alloy rather than pure zinc , the engineer may well be correct. We know that brass, which is an alloy of zinc and copper will give up its zinc content in an electrolytic situation and it could well be that if an anode has already significantly erroded; the zinc content will have reduced over the entire surface and probably to some depth. This would mean that if it was melted down and re-moulded the "new alloy" could well have too lower zinc content to be effective. Not totally sure but I can see some sense in what he is saying.
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02/06/08 13:06
 See my comments on boat aground on Loch Ness. My riser in what is very acidic freshwater near my lead keel degenerated in 5 yrs to paperclip thick bright metal-thru electrolysis/galvanic action. Local owners who also moor on Loch Ness now realise that we all have the same problem. Had already noted how quickly chain had lost heavy hot dip galvanising. Phil
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02/06/08 22:01
 Hi Phil, I am a great fan of ignoring the whole method of 'rising chains' would a great lump of ground chain, attached to a length of polypropelene with swivel and buoy be a much more robust method of mooring? We do this a lot in my area and as long as you replace the 'tackle' end every few years seems to be very robust.
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03/06/08 09:11
Whoops should have said polyethylene - not polypropelene
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03/06/08 13:36
Issue for me is that in freshwater you wouldnt necessarily expect this problem-on my west coast mooring I use a polysteel riser-although have had problems with swivels on this resulting in the origional three strand untwisting-now replaced with multiplat. Phil
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03/06/08 15:44
I'm not a chemist Phil but there may well be two different things here. I think the problem in Loch ness is due to chemical reaction rather than electrolytic action and sacrifical anodes would not make a scrap of difference.
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03/06/08 20:45
I am not really sure what happened but in a fresh water environ. those who share our little group of moorings near Fort Augustus all have been lulledinto a false sense of security-after all galvanised chain in fresh water. Turns out that my boat was not the first to have parted co. from its anchor block. Chain end which had spent last five years buried in mud was for its bottom two feet bright and shiny and suffered metal loss down to little more than several mm.in places. I suspect what ever reaction took place occured in the silt layer. Clearly an unusual problem and as there are probably no more than thirty boats in total moored along the Great Glen not really of general relevance BUT interesting non the less. Phil
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Hi All This is my first time on line here so be gentle with me! I read the article on sacrificial protection and the use of old anodes Would you recommend that the old anodes are bonded to the boats normal earth system not just hung over the side from an electrically isolated handrail or grab wire? If you have a galvanic isolator would this be effective? In the past I've seen special sockets for connecting anode that hang over the transom of yachts, that change from fresh to salt water regularilly. I know that these sockets are conneted to the boats earth system. for the sake of clarity when i mention earth I'm talking about -ve not shore power earth I'd be keen to hear what peoples opinion on this is as an electrical engineer Regards Paul
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25/06/08 18:39
If you really want to start a major electrolysis problem start connecting everything together, you'll create a superb battery and dissolve all your metals one by one! If things of dissimilar metal are not connected to eachother - they cannot get electrolysis - its a simple law of physics, where things of dissimilar metals are connected, and of course immersed in the sea (the electrolyte) then obviously one needs an anode - ie on a prop shaft or sail-drive, other than that there is not problem. Remeber nothing happens in a battery until the pole of the battery are connected - simple isn't it! So if one starts wiring skin fittings and rudder stocks together - be warned they wont last five minutes!
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