anode protection for french canals

[atlowers]

wow, thiss has become a tricky problem? I am taking boat over to French canals for 6 months and leaaving it there over winter. Boat will be in salt water for 4 weeks before trip. My understanding is that I must have magnesium in Fresh but these will last very limited time in salt. (manufacturerss have suggessted 2 days at most) I have ruled out hanging anodess for such a long period as tricky to fit conjusive to live aboard situation and will not protect on the move when most necessary.
Q1. anybody any thoughts on this as I dont want to lift overthere just to change anodes and not prepared to attempt hull anode replacement with boat in water. I want to stop in st valerie for 3/4 days which is salt water before entering canal system.
Q2 And after all that does anybody know a manufacturer of magnesium shaft anodes 1.5inch. My searches are exhausted. If not I am forced into fitting brush system.

I am amazed that this has been such an issue particularly the issue with manufacturers stopping production of 1.5 inch shaft anodes. Surely many people have this problem and yet it seems such a grey area. I would be delighted to hear of other peoples experiences and particularly any horror stories as the manufacturers seem to have many where people have not protected the boat properly.

Thanks and sorry for long post.

 

[pcatterall]

I await answers with interest as I am in the same position.
We have been in Preston Marina for 6 months and I posted recently about the dicolouration without wear on my annodes. I wonder if this is because the water is not very salty there. No sign of problems on prop or shaft though.

 

[vyv_cox]

I would not worry too much about it. I kept my boat in fresh water in Holland for seven years and used zinc anodes throughout. We sailed on the sea most weekends but sometimes only on fresh water. Anodes developed a white coating of hydroxide that is an insulator but I suggest they still performed to some extent. No prop corrosion has occurred.

 

[Quandary]

An almost identical question was asked very recently.
I keep my boat in fresh water (Crinan Canal) but because we spend several weeks at a time in the sea I have to use zinc anodes rather than magnesium and the zincs are affected by a passivated coating within about three weeks. I overcome some of the risk by supplementing an easily cleaned hanging anode wired to the most vulnerable item, the sail drive leg. However this is just because aluminium anodes are not available for my leg or prop.
I was looking at the aluminium shaft anode on the boat ashore next to mine at the weekend and it seems clean and to be eroding satisfactorily and the owner swears by the effectiveness and longevity in the fresh/salt water environment.
I would be surprised if you could not find aluminium shaft anodes simply by googling for them, most anode makers make them, it is only when you have saildrive propulsion that it is a problem. However since your problem is the shaft diameter I suspect that you may be caught like us saildrive owners but it should be a lot easier to fabricate a shaft anode than the odd shapes that you need for the saildrive. I do not know enough about metallurgy to advise if aluminium is as easy to smelt and turn as zinc but it must be easier than magnesium.
My last boat was shaft drive with a folding prop. and at one time it spent 18 months in the canal with a few trips to sea, protected by only two zinc shaft anodes without any detectable ill effects. A lot of the other boats here that are in the canal all the time with briefer trips to sea are very relaxed about this whole anode business without any apparent problems.
In your position I would try to get aluminium anodes made or modified, it is just a cylindrical billet with some holes in it, failing that I would go with zinc but ensure that they are cleaned within a couple of weeks of returning to salt water after a long period in fresh. I can not guarantee that you will not get corrosion in fresh water particularly if you are on dodgy shorepower for long periods but a galvanic isolator is the answer to that.
After all there are a lot of boats in fresh water most of the time and their owners seem to worry less than you or I do.

 

[atlowers]

Thanks for the reply quandery, I can get aluminium shaft anodes no problem it is just the magnesium that is the problem. I did see the previous thread but hanging anodes are an option I have discounted. I was hoping for the type of feedback you have given of people who have experience of this type of situation as I am dubious as to just how crucial it is to have magnesium for my extended trip and it is the anode manufacturers who have been adamant that aluminium will also pasivate in fresh water and result in no protection and resultant damage. This is difficult to ignore but theory and practice are often at odds so
keen to hear any other personal experience to base a decision on. ie how long in fresh before damage potential if running with aluminium.

motivation to get it right comes from money just spent on repitch and refurb of badly pitted props and advised that the pitting was probably caused by just this issue in the boats previous ownership.

 

[Grehan]

I would not worry too much about it. I kept my boat in fresh water in Holland for seven years and used zinc anodes throughout. We sailed on the sea most weekends but sometimes only on fresh water. Anodes developed a white coating of hydroxide that is an insulator but I suggest they still performed to some extent. No prop corrosion has occurred.

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