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Jeffrice
Jeffrice

Posted: Tue Jul 19, 2016 5:45pm

Post Subject: Anodes

I've heard people making disparaging comments about anodes, saying that they don't really work. What do you think? Yes or no to anodes?

Tony-B
Tony-B

Posted: Tue Jul 19, 2016 10:21pm

Post Subject: Anodes

So all the boat builders who fit anodes as part of the build and all those boaters who pay to have their worn anodes replaced are wasting their money? Immerse dissimilar metals in an electrolyte (dirty or salt water) and they will form an electrical cell. Depending upon which direction the current flows in that cell either your hull or porpoise will be eaten away. Attach a more reactive metal to the hull or shaft and that metal will be eaten away in preference to something more important. Hence the use of anodes. If you fit zinc anodes for fresh water use it is not reactive enough so it will not protect or be eaten away much. Fit magnesium anodes in salt water and they will be too reactive and will be eaten away too quickly - as can be seen by fizzing narrow boat anodes in places like Liverpool docks. Anodes are unlikely to provide sufficient long term protection if you have an electrical fault on the boat or use a shoreline without a galvanic isolator or isolation transformer or even, in some cases, moor close to a boat with a problem. It is far too easy to say anodes do not work when you allow electrotype to eat your hull away. I is also true that the area of influence of an individual anode is limited and many narrow boats actually have no or very little protection in the centre part of the hull. This is a build/design problem not one that indicates anodes do not work.

Tony-B
Tony-B

Posted: Thu Jul 21, 2016 9:21am

Post Subject: Anodes

A further thought on this. If, and its a great big set of ifs, you have your hull totally coated in a modern two pack hull coating and IF you never puncture that coating then the coating will act as an insulator so any galvanic activity will be very much reduced or even halted. Personally I suspect it would all be concentrated on the inside of any steel tubes or bushes used to fit the stern gear into the boat. I can not see the second if ever being met unless the boat never leaves its moorings and the first if is questionable because to fully coat the base plate takes work to move the hull supports. It is worth noting that outdrive and outboard motor manufacturers often fit anodes behind the prop as standard. This is because the cases are often cast aluminium and they do get eaten away without anodic protection. You can also use what i think is called impressed current protection like they do on ships. This is where the hull is deliberately charged with electricity to control galvanic corrosion but sufficient anodes will be far cheaper for typical inland boats.

Jeffrice
Jeffrice

Posted: Tue Jul 26, 2016 5:33pm

Post Subject: Anodes

Thanks Tony. Anodes it is :)

Jeffrice
Jeffrice

Posted: Tue Aug 02, 2016 1:58pm

Post Subject: Anodes

Hi Tony, Additionally - After pressure washing my hull, I've got these very bright shiny spots. One person suggested that this was the result of the anode reaction. Plus, the colour doesn't quite look like steel, so I'm wondering if this also is part of the anode reaction?

Anodes
Jeffrice
Jeffrice

Posted: Tue Aug 02, 2016 2:01pm

Post Subject: Anodes

....not sure if you can enlarge that pic, so here's a cropped close up...

Anodes
Tony-B
Tony-B

Posted: Tue Aug 02, 2016 4:28pm

Post Subject: Anodes

I do not work from the Canal Boat office so can not get access to your raw postings but in any case I suspect the forum software shrinks all photos to an unusable size. If you want me to look at it please email it to Tony@tb-training.co.uk but as I am on mobile broadband out in the country please do not send high res. photos. If the pits were filled with slime before you washed the surface away it could well be microbial corrosion. If you have mains aboard without a galvanic isolator or isolating transformer then it could be active electrical corrosion. It could even be that if you have an older GI that conducts at a lower voltage than modern ones do. If the surface looks like zinc plating then it could be related to excess anodes but if this is the case it should be within a few feet of the anode and possibly very close. If you close moor in a marina it could even be caused by a mains electrical fault on an adjacent boat using your hull as part of the path to earth.

Jeffrice
Jeffrice

Posted: Thu Aug 04, 2016 1:45pm

Post Subject: Anodes

Hi Tony, Emailing you the pictures now...

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