Update on Shaft anode

[Spyro]

Ref to previous post
http://www.ybw.com/forums/showflat.php/Cat/0/Number/1282196/an/0/page/2#1282196
Response from MGDuff

<span style="color:blue">There are a number of reasons why an anode will not corrode, for instance not being in electrical contact with what its trying to protect, but it looks like in this instance that the anode has formed a passive film on the surface preventing the anode from corroding. This passive film (a stubborn oxide film) can occur due to a variety of reasons and the most common is if the zinc anode has been used used in brackish or fresh water environments. The alloy used in zinc anodes contains elements designed to aid the corrosion of an anode and the corrosion products (zinc oxide) generally get washed away in fast flowing water. If the vessel is moored for a long period of time the zinc oxide can form a stubborn film on the surface, again, preventing the anode from working. A passive film can also be formed if the iron content in the alloy is too high and you should always insure that your anode conforms to the US Military specification 18001K.

I hope that has answered your question, if you do require any further information please feel free to contact me.

</span>

 

[Richard10002]

If this was the case, wouldnt you expect the whole anode to be covered in the stubborn oxide.

 

[nedmin]

Altho. anodes do work its not an exact science I dont think!!!!. My first steel boat had an alongside mooring against steel piling,the anode away from shore always wore down a great deal more than the one against the piling. There were no other boats on the outside within 50yds.Can anyone explain that?

 

[DAKA]

Silly question and no doubt you have already thought of this but could you have caught the anode when antifouled and wiped half the anode with paint/thinners ?

Even a splash of antifoul/grease will protect an anode as the clear space is an easy target.

 

[mickshep]

In a similar vein. I'm about to fit a shaft anode to the stainless steel shaft on my boat. Should it be bedded on anything to give a better contact between the metals? Or do I just rely on the face to face contact? Cheers, Mike.

 

[sailorman]

clean the shaft locally with 150 grit glass paper or similar clamp anode in place with the fixings provided. when tight, hit both sides of the anode smartly with a hammer ( 6 > 8 oz ) then re-tighten fixings

do not use anything to bed / insulate anode on the shaft

the best anodes imho are the M G Duff with the steel strap cast-in, they last longer & dont come loose

 

[Spyro]

[ QUOTE ]
If this was the case, wouldnt you expect the whole anode to be covered in the stubborn oxide.

[/ QUOTE ]
My thoughts too.