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Anodes


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Okay guys, yet another question from the newbie saltie corner :oops:

ANODES!

If I have read things right, I understand that the anodes should be zinc if the boat is used in salt water, and magnesium if used in fresh. Am I right so far?

1. How can I tell what the anodes I have are?

2. If the boat has magnesium fitted as it spends 80% of it's time in fresh water, does that mean that it'll start to rot as soon as it goes to sea (ie the other 20%)?

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It should be pretty obvious if you take one off and feel the weight Mark, but you can tell from looking. I always used aluminium when alternating between fresh and saline and that worked well. Mag ones will not last long at all in anything saline, more akin to Alka Seltzer

Some good reading on the MG Duff site, that's all they do.

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Intersting, I've just read the MG Duff site, and there is some interesting information. They recommend against Aluminium for prolonged fresh water use, as a layer of oxide will build up rendering the anode useless when returned to brackish or salt water. On the other hand, they do not recommend magnesium for any more than 14 days in one year in salt water, and no period longer than 7 days at a time.

I think I'll stick with magnesium for now, and see how our sea-going pans out!

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Aluminium ones tend not to get an oxide layer on the lower reaches which are quite saline so it depends where you park really. Drives are not Aluminium but rather an Aluminium alloy which is further up the galvanic scale than the pure Aluminium used in anodes. Our Ship has just been lifted for a couple of months and despite fitting new zinc anodes last summer the prop anode is borderline in need of replacement, as are the two skeg anodes, the two trim tab ones, the thruster one and the two rudder ones, the only one that is still acceptable is the 2kg bonded bar on the transom.

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hi Mark performance metals do a set of alluminium anodes suitable for use in fresh and salt. Have a look on ebay or aquafax for prices but for the 290 dp they are about £50 per leg.

They are the ones we use and they have worked well so far.

Ian

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hi Mark performance metals do a set of alluminium anodes suitable for use in fresh and salt. Have a look on ebay or aquafax for prices but for the 290 dp they are about £50 per leg.

They are the ones we use and they have worked well so far.

Ian

Thanks Ian, I'll check those out. Being in Reedham, I'd guess you were a little more brackish than us?

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hi mark!

I can also recommend Performance metals as a brand as we also fitted their aluminuim anodes to jupes. We are based at Goodchilds in Burgh castle, and apart from the Royal Norfolk, I dont think you could get closer to salty side. On lift, after 9 months they seem to have survived very well. My feeling is that if you spend two days of the year in the salt and 363 in the fresh...you have your answer!

Check with other owners whose boats are moored where you are...as I am sure their boats will spend more time just sitting there and will give you a good idea of what works best where you spend the most time.

adam.... :pirate :pirate :pirate !

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This may sound silly but can you not use both?

I have salt annodes on a boat I have but as she is sitting in fresh water I bonded every annode and all metal (rudders, shafts etc) then bolted fresh water annodes to the wire which I hung one over the back and dropped one in the bilge. they are being eaten a bit so I assume they are working, or am I wasteing time?

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Hi Clive, I may be wrong but I would suspect that the different metals in your anodes would set up a current between themselves so your magnesium anodes would flow to your zinc and as such get eaten up by offering protection to the zinc anodes.

Ian

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Ian is right, all you have to do is look at the galvanic scale, all the lower metals will protect the ones above them in the right conditions. So for instance if (in salt water) you had a drive protected by Mag, Ali and Zinc, the mag would protect the ali, zinc and drive until gone then the ali would protect the zinc and drive until gone and so on...

They are all much less effective if they have an oxide layer so it is important to make sure they are "bright" before launch.

For those with drives the worst possible combination is the drive and SS props.

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I'm still not 100% convinced with the Aluminium option, so can anyone help me understand a bit better please? I am sure they are okay in the brackish water around Reedham and Burgh Castle as that is what they are designed for, but the fresh water at Brundall I'm not so sure.

What I read about the Performance Metals ones states they are suitable for fresh, brackish or salt water. Reading on other sites, though, they say that in fresh water the aluminium will get covered with an oxide layer, meaning they will be ineffective when placed back into salt. However, the Performance Metals info claims the oxide layer to be porous and therefore allow water through and hence still work in salt after a time in fresh. If I remember my chemistry properly, I thought both Aluminium oxide and Zinc oxide were impervious to water, which is why they don't rust outside, just get covered in a white layer.

On lift, after 9 months they seem to have survived very well.
Again, Adam, most of the time your boat is in brackish water so they are in the correct environment. Also, though, an anode surviving could mean it's not working couldn't it?
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