Hanging anodes

[wp1234]

Just had a quick look at my prop shaft anode with an underwater camera and it looks pretty well wasted to me .Now that its December I was hoping to stretch my annual lift out my seemingly fizzing Marina until April 09 but I doubt if my anode will make it till then .
I’m on shore power most of the time (float charging , heater and dehumid ) .I have a galvanic isolator fitted but I still like to be belt and braces with anode protection.
Just wondering if anyone has any advice on hanging anodes .I was thinking of bolting a couple of old anodes together and hanging over the side with some steel wire .It seems to me that clamping the wire onto the prop shaft would be ideal but what sort of clamping would I need and is this really effective.
Thanks in advance

 

[bazobeleza]

I have a hanging anode that gets used when in a marina, it lasts about a year so it must be doing something, its on a line level with the prop. it doesn't seem to waste when at anchor, only in marinas when on shore power.

I've checked for any stray currents but have found non, so there must be some on other boats.

 

[me2]

We hang a ZD56 over the back , hanging on 44/3 wire going to the earth bolt of the main anode , if you go to the shaft you will need to bypass the gear box , we also do that so everything is bonded

 

[VicS]

[ QUOTE ]
if you go to the shaft you will need to bypass the gear box

[/ QUOTE ] But if the stern gear is the target to protect then the shaft is the best place to connect it to. Just dont start up without removing it!

A galvanic isolator should prevent problems with shore power connections in marinas.

Trouble with marinas is that if you connect the shore power without a GI then your anodes are busy protecting all the steel piling as well as maybe the steel boat in the next berth and thats without any dodgy electrics in nearby boats.

 

[me2]

If you use one of MG McDuffs Electro Elininators you do not need to disconnect it when you start up do you , and that way the shaft is bonded to the main anode

 

[samwise]

You really need galvanised wire. I rigged an overside anode for our boat using a shaft anode bolted to the wire and run to the bonding circuit. Don't forget to slip a length of plastic pipe over the wire to protect the paintwork where the wire goes overside. I had just completed a trip up the French canals, which had passivated the zinc anodes on the hull and shaft. The magnesium fresh water anode I had managed to fit to the shaft before the canal trip dissolved within days of getting back into the salt stuff and my overside anode provided a stopgap solution before hauling out.

 

[najsmith]

I only have shaft anodes for our boat.

Been meaning to run a thick earth wire from the engine block to a connection plate in the starboard locker. This would enable me to easily attatch some wire with anodes bolted on, and hang over the side.

I feel the incresed use of power aboard boats in marinas means I need extra protection when stopping over.

That said I do prefer sitting on our swinging mooring or dropping the hook...

 

[VicS]

[ QUOTE ]
This would enable me to easily attatch some wire with anodes bolted on, and hang over the side

[/ QUOTE ] but don't forget to bridge any flexible coupling in the shaft to complete the circuit.

 

[jerryat]

>>.....I had just completed a trip up the French canals, which had passivated the zinc anodes on the hull and shaft..... <<

How did you know this? I mean, what are the signs that an anode has 'passivated'? /forums/images/graemlins/confused.gif

I ask because we spend almost six months the year before last, going down the French canals/rivers to almost the Med. and back. When the boat was lifted out back here for the winter as usual, there was the expected annual degree of minor anode erosion we normally get, and the anode looked identical to normal in every respect.

A continuity check on all items connected to the anode was perfect, and certainly absolutely no corrosion of the protected items had taken place. /forums/images/graemlins/smile.gif

Really would like to know how one identifies the passivation 'problem', as we are thinking about heading off cruising in the Med. again and may go down the canal route this time as a change from the 'outside' route. /forums/images/graemlins/smile.gif

 

[Guest]

I've often thought that a galvanised anchor and chain makes for a very effective (and expensive) hanging anode, especially on a steel boat. I'm sure there's a case for insulating the ground tackle from the steel hull, but I don't know if anyone ever bothers.

 

[VicS]

[ QUOTE ]
Really would like to know how one identifies the passivation 'problem'

[/ QUOTE ] It is something that will happen. MG Duff recommend fitting magnesium anodes for any period exceeding 2 weeks in fresh water. Although they do not specifically say so the implication is that this is the sort of time period in which zinc anodes will become passivated. I suspect though that many factors will affect this.


I have no details but it should be possible to monitor the protection your anodes are providing using a reference electrode such as a silver/silver chloride electrode. It would be interesting to hear from anyone who does this.

 

[jerryat]

Hi Vic,

Yes, I can see the sense of using a magnesium anode and have no problem with that.

What I am trying to find out from Samwise's post, is how he KNEW the anodes had suffered from passivation.

As I posted earlier, I could see no difference in the anode at all after almost six months in fresh water so it appears that I'm missing something potentially significant.

Would appreciate Samwise's help.

 

[wp1234]

[ QUOTE ]
If you use one of MG McDuffs Electro Elininators

[/ QUOTE ]
web page


have'nt seen these before - Does the panel think that fitting this to the shaft then running earth cable from it to the larger ( and easier to replace ) anodes make the end of shaft anode redundant @

 

[me2]

No it will help the prop anode, the gearbox does not have a good earth going through it due to the moving parts , so by fitting one you are making sure there is a good bond to the shaft. The thing is the prop anode is to small as to what it looks after. I have a Merry Fisher too and as I said I run the wire to the anode bolt on the back and have the shaft bonded, this way everything has a good bond and thats what you need. By doing this the anode on the back will also help to look after the prop.

 

[VicS]

Yes, this this is the best way of making a good connection between a hull anode and the stern gear, There is then no need to bridge the flexible coupling, or any fear that the bridging connection will be thrown off and it eliminates the possibly poor circuit through oil lubricated bearings if the connection were made to the engine block or gearbox casing.
If there are any other items to be protected by the anode then they would have to be bonded directly to it.

See also MG Duff's website

It is not phenomenally expensive but fitting it may be complicated so you have to decide if it is worth the trouble. If there is no corrosion problem with the stern gear then it may not be worth it. If a shaft anode can be fitted then that may be the easier option as, IIRC, has already been suggested.

Do you actually have any corrosion problem with the stern gear or are you just trying to avoid replacing the little shaft end anode so frequently?

 

[wp1234]

Hi Vic S and Me2,
Thanks for the advice and warning about expense. I‘ve had my MF 805 in the water for just over 10 months now and have fitted two shaft anodes so far. Having looked at the second 35mm shaft anode recently via a friends underwater camera I can see its just about gone now. I have fitted a galvanic isolator a few weeks ago so that will help when I’m on shore power. I have just the two anodes shown on the picture .The transom one lasts a full year and is easy to change but the much smaller shaft one seems to go very quickly.
There are no obvious signs of corrosion anywhere so this is all a bit precautionary. You’ve got me thinking wether I need to worry about it to much – what’s the worst that can happen if I have a shaftless anode for a few months at least until I take the boat out.



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[me2]

Thats the same as mine , the prop anode is very small compared to the prop. I use the hanging anode for piece of mind. I tend to connect a wire to the bolts on the coupling and then the other end to the earth/bonding wire on the fuel filter I always turn the seacocks off when not using the boat and the wire I use is run over them so I cant forget to take it off ,if I forget I cant turn the cooling water on.
Someone down the pontoon from us stores loads of gear in the locker which the anode bolt is in, he knocked the bonding wire off and when the boat came out this year he now has a very pink prop.

 

[VicS]

First reaction is that the transom anode is far from being in an ideal position. It may not be far away from the prop but it fails the "within line of sight" criterion. That may not need to be taken too literally so perhaps it's ok.


One thing is for sure is that such a tiny anode as your end of shaft one so close to such a huge area of copper alloy prop is never going to last very long so don't expect the GI to have a great effect on its life.

If your prop is a decent manganese bronze, not brass, it should not in fact need any protection especially with a GI in the shorepower connection. What will happen if you allow the shaft anode to decay completely rather depends on what the prop is made of.

How is that transom anode bonded at present ? It's not another one thats doing nothing because its not connected to anything is it?

 

[wp1234]

Hi again Vic S,
The transom anode is well bonded to the rudder stock and i'm sure its also bonded to the P bracket but will check this weekend just to make sure.
I've no idea what the props composition is though.
The single transom anode is about half wasted at the moment so its doing something I guess .