What's eating my anode?

[alexincornwall]

Brace yourselves for potentially daft questions, I’m an anode amateur.

We’ve just been hauled out after 10 months in the water. All good but I was a little alarmed to see that the only remains of our brand new prop anode were its stainless fixing studs and the internal circular insert. The hull anode looks to be working as expected and as usual (maybe 25% eroded), as are the bower thruster anodes (50% eaten). The max-prop anode has always been the weak link on our boat as a design flaw (in my opinion), means that the fitting holes are positioned very close to the outer edges of the anode. Saying that, in previous years of similar use, we’ve always come out with 25% remaining. Concerningly, I have no way of knowing exactly when the anode disintegrated – it could have been months ago!

For context we spend around three months a year on shore power, haul out for one month, and then spend eight months on our swinging mooring. Batteries are always isolated at the breakers when we’re not onboard and our battery monitor always show zero current. I can’t see any indication of stray current.

We have had some electrical work done this year to include new batteries and a full solar install. So, my questions are:

Is it possible to simply be a victim of a duff anode?

Could the charge generated through solar accelerate anode erosion?

If there is a reason for the accelerated erosion, why have the hull and bow thruster anodes behaved as expected?

Would the other anodes continue to offer protection to our stern gear after our prop anode bit the dust?

 

[vyv_cox]

This used to occur with Bruntons prop anodes. It seems the anode tries to protect the fastening bolts, so wastes rapidly there until it falls off, only partially corroded. Bruntons' cure was to supply nylon bolts, which has fixed the problem completely.

Some people report that coating the anode with nail varnish around the fastening holes does a similar job.

 

[Graham376]

That used to happen with our Featherstream anode. Cured it by dabbing antifoul around and in the bolt hole areas and there's still enough contact area around the base for protection.

 

[Jmc1764]

Same thing with my Maxprop, first year the anode was almost gone, someone in the club said paint the bolt holes, second year about 50% gone, so I assume there must be some reaction between the stainless bolts, the bronze prop and the zinc, I also cleaned up the surface where the anode fits against the prop, not sure if that helped but prop was fine. This year I took the prop off for a service, ( its about 30 years old) and cleaned all the paint off, what was surprising is that it looked like where barnacles had been they had sucked the metal out of the prop, there were little round areas that had gone copper colour, a bit of sanding with some fine wet and dry removed the micro layer and bought it back to the nice bronze colour. It was surprising that had happened through several layers of paint !

 

[alexincornwall]

Thanks for the replies, I will suitably antifoul/nail varnish the bolt holes ahead of relaunch.

Is anybody able to answer my other questions, specifically whether or not a live solar installation would have any affect on the anodes, and if the other anodes continue to protect the stern gear if that one erodes prematurely?

 

[VicS]

Thanks for the replies, I will suitably antifoul/nail varnish the bolt holes ahead of relaunch.

Is anybody able to answer my other questions, specifically whether or not a live solar installation would have any affect on the anodes, and if the other anodes continue to protect the stern gear if that one erodes prematurely?

A solar installation should have no effect on the anodes. Something seriously wrong with the installation if it does!

Other anodes will only protect items to which they are bonded. There must be a good low resistance connection between an anode and the item(s) it is to protect.

 

[PaulRainbow]

Thanks for the replies, I will suitably antifoul/nail varnish the bolt holes ahead of relaunch.

Is anybody able to answer my other questions, specifically whether or not a live solar installation would have any affect on the anodes, and if the other anodes continue to protect the stern gear if that one erodes prematurely?

Was just going to post what Vic said, so i'd agree with post #6

 

[VicS]

Was just going to post what Vic said, so i'd agree with post #6

Ta

 

[alexincornwall]

Many thanks, useful to know.

 

[blush2]

Same problem with our Volvo folding prop three part anode. We've used all the old car touch up paint up over the last 19 years (the sort with an integral brush).

We used to be on a pile mooring with pontoon in the Hamble, people said it can be caused by the chains, old ironwork on the river bottom, etc. Rarely went in a marina. Interestingly, when we spent a year away, going down to Portugal, the Canaries and Azores, the anode lasted a lot longer despite the fact we spent a lot of time in marinas.