hurky
regular
Reged: 15/07/2007
Posts: 15
Loc: Eastbourne
|
|
Before we enter the French Canals this year we are changing our zinc anode to a manganese one. It will probably be at least a couple of weeks before we go from saltwater to freshwater completely. During that time, we are considering temporarily connecting zinc shaft anodes to be attached to a stainless steel tube lashed to the boarding ladder and electrically bonded. Can anyone see a problem with having two types of anode connected at the same time or am I being paranoid?! Any feedback welcome.
|
whiteoaks7
regular
Reged: 29/11/2002
Posts: 244
Loc: South Wales, UK
|
|
I wait to be educated here, but I think the magnesium will protect the zinc - ie it will fizz away and the zinc and your boat will both be protected (cathodic to it).
This article is a bit confusing but may help: http://www.pelaginox.com/data/d-galvanic.html. I can't actually find a table on the web that includes manganese so my assumption is this is more active than zinc (since fresh water is a poorer electrolyte). In short - just rely on your manganese and if you're really worried tie a manganese anode to your ladder rather than a zinc one, this will have the added benefit of allowing you to measure the rate of erosion.
--------------------
David Berry
(Free software for sailors... www.seasolutions.co.uk)
|
cliffb
regular
Reged: 09/03/2004
Posts: 378
Loc: SW Scotland
|
|
Paranoid I'd say.
More to the point though, is it worth changing at all - from salt to fresh water, that is. And this will depend on how long you intend to stay in the canal system. If it's only a few weeks then personally I wouldn't bother. I spent 4 weeks in the Caledonian canal last year with zinc anodes. On haul out I could see no discernable difference to previous years when I was in salt water all season long.
Have a good trip though... you lucky b***ers!!
|
whiteoaks7
regular
Reged: 29/11/2002
Posts: 244
Loc: South Wales, UK
|
|
One extra thought that people might want to comment on - pipeline people (gas, water, oil etc) use impressed cathodic protection schemes. They force a current the 'wrong' way in order to make their pipelines cathodic. This is far cheaper to them than using sacrificial anodes like zinc. This impressed current idea should be translatable to boats so a small voltage source between anode (whatever it's made of) and hull fittings configured to ensure the anode remains anodic whatever the electrolye, aught to work. Anyone ever heard of this being done?
--------------------
David Berry
(Free software for sailors... www.seasolutions.co.uk)
|
vyv_cox
regular
Reged: 16/05/2001
Posts: 4525
Loc: North Wales, sailing in Medite...
|
|
I think you mean magnesium. Although the text books will tell you that you need to use magnesium anodes in fresh water, this really only applies if you are inland permanently. Even then, zinc will not come to much harm, or you could use aluminium anodes which supposedly are OK for both fresh and sea water.
I kept my boat inland in Holland for seven years, with excursions into the sea at some weekends and all holidays. I used zinc anodes throughout. The only problem is that zinc hydroxide forms on the surface and needs to be abraded off occasionally.
There is a strong likelihood that your magnesium anodes will be completely consumed by the time you get into the canals. It reacts strongly with seawater.
Overall, how much corrosion of your boat do you think there will be while you are in the fresh water canals? Answer - very little. Don't panic, do nothing.
|
davewarburton
regular
Reged: 17/10/2003
Posts: 585
Loc: Me Scotland; Boat France
|
|
OK - we have this problem as we are berthed in fresh water but sail at sea - and I mean fresh water - its 5km up a river locked in from the sea.
We have Aluminium shaft and hull anodes and they seem to work OK. When in the fresh water marina I hang a Magnesium anode from the stern as close to the prop as possible. It's bonded internally to all the points that the Aluminium one is.
When in salt water but not actually sailing, I hang a zinc anode from the stern as above.
So far it all seems to work. If you are only going to be in fresh water for a short time, then the comments above about not needing anything other than your zinc are probably correct. However, as already stated, the zinc will oxidise in fresh water and become ineffective until you clean it up.
Hope all this helps
|
macd
regular
Reged: 25/01/2004
Posts: 755
Loc: Ayamonte, Spain
|
|
davew's suggestions make sense to me.
The problem with zincs in brackish water is that they can be contaminated with a layer of zinc salts, which stops them working even when the boat returns to the sea -- unless you physically abrade off the coating. From personal observation, some boats seem to suffer this whilst others don't, even moored in close proximity. It'll be something worth checking when you reach the salt again.
MG Duff's website has lots of relevant info. Maybe worth an e-mail to them?
|
hurky
regular
Reged: 15/07/2007
Posts: 15
Loc: Eastbourne
|
|
Quote:
Don't panic, do nothing.
Grateful for all the input, I think it might be the case of taking the advice of vyv_cox: If in doubt do nothing! I think we may have been worrying unduly.
We will be wintering in Port St Louis area, before sailing off into the Med next year, so will definitely check the zinc anode then. Thanks all.
|
Grehan
regular
Reged: 11/06/2001
Posts: 1167
Loc: Inland France
|
|
Concur with the "don't panic" advice. I don't think you'll have any kind of problem, inland in freshwater.
However, if you have a steel boat you need to be that little bit more careful, even inland. But I'm sure if you've got a steel boat you're only too well aware of the potential for electrical corrosion problems. 
The MG Duff website is very helpful www.mgduff.co.uk
--------------------
___ Grehan :: French Waterways information ___
|
Roadkill
regular
Reged: 14/09/2005
Posts: 34
Loc: Yorkshire
|
|
I have a steel boat and I too am trying work out what I should do regarding anodes. I'll eventually be moored in salt water, but for the first year while I get used to living aboard and sort out the interior etc. I'm thinking of bringing the boat, sans masts, up the canals closer to where I work. I'm going to get 6 pairs of studs welded to the hull and two the rudder, this way I can interchange between various anode types if necessary, but I have a few questions:
Do I still need shaft, prop anodes etc. on a steel boat, or does the fact that I have hull anodes override this?
Are the welded studs meant to be left unpainted?
Would I need to change to magnesium anodes for the canals, or could I just dangle a lump of magnesium over the side, and clean up my zinc anodes on return to salt water?
Any other advice regarding anodes and cathodic protection, salt vs fresh water for steel boats, for a total beginner?
Thanks,
--------------------
Dave Hall
Sailing Novice Extraodinaire
http://seawych.spaces.live.com/
|
Previous
Index
Next
Threaded
Edit
Reply
Quote
