Best anodes for sea water: zinc or aluminum

[Wavey]

HI Wavey,
I went over to the aluminium after realising all the Mercruiser anodes were aluminium.
And thinking Mercruiser are a big company they must know what they are doing.
I have noticed Mercruiser boat owners and service operatives then put Zinc on the trim tabs which I thought would be counter productive.
Have you noticed any jelly like substance coming off your anodes ?

I only switched to ali anodes in September and boat hasn't been lifted since. It's due out late March/early April for antifouling so I'll post what I find then.

 

[Bouba]

Inspired by this thread, this morning I anchored in a calm bay with clear but cold water donned my wet suit and armed with a wire brush I cleaned off my anodes. I was too buoyant to do the propeller anode but I think they should just about last until my haul out beginning of April.
I definitely am going to invest in a stiff scrubbing brush on a long pole so next time I can do it from the swim platform or the dingy

 

[Dog's dinner]

Hi Wavey,
Do you have sight of your anodes on your trim tabs ?
Are they crusted and can you see any jelly like stuff coming off them ?
I think I have attached 2 pictures. taken couple of weeks ago 6 months in water.
Picture 1 is showing the jelly stuff growing out of the anode.
Picture 2 is showing the crusting on them.
When I spoke to the manufacturer of the anodes he said aluminium anodes
don't crust much and should be shiny, that's their benefit over zinc.

 

[Portofino]

Hi Wavey,
Do you have sight of your anodes on your trim tabs ?
Are they crusted and can you see any jelly like stuff coming off them ?
I think I have attached 2 pictures. taken couple of weeks ago 6 months in water.
Picture 1 is showing the jelly stuff growing out of the anode.
Picture 2 is showing the crusting on them.
When I spoke to the manufacturer of the anodes he said aluminium anodes
don't crust much and should be shiny, that's their benefit over zinc.

Any other variables?
Same mooring - where ?
Same neighbors?
Same water temp ?

You said earlier you had all your electrics checked - galvanic isolator , DC leakage ? Etc .
Same shore power cable ? and same box as “ previous years “

Maybe a neighbors now got massive Zinc s and those Zincs being higher up the table and physically close are making your AL alloy anodes react ?

All based on the exact same material as your manufacturer claims as per previous years .
Obviously if that’s changed there’s your answer , but until proven otherwise let’s assume they are actually the same .

 

[Dog's dinner]

Hi,
Yes the same berth in Poole.
Same neighbors, other side of finger no one next to us.
My galvanic isolator has DC and AC leakage warning lights which I have tested and confirmed working with the manufacturers.
So any leakage would show a warning light.
The boats bilges are always dry as is the rest of the batteries wiring etc. ( I am a bit fussy )
Apparently all the anode manufacturers use to a set mix.
And they were from different annual purchases.
We only plug in electric from December to March for the tube heaters.
The only change that could have been was the water temperature as we had an unusual good summer.
I am going to lift the boat in May / June 2.1/2 months early this year so will be interesting to see what they are like then.
But the mystery this year is the strange jelly like stuff coming off them with the crusting I have not ever seen this before.

 

[B58]

In thirty odd years of outdrive ownership, mostly Mercruiser, I never knew that!!! Have always used Zinc and they seem to have done their job.
So how does an aluminium anode protect an aluminium drive?
I shall have to look into this some more.......

The drive is an aluminium alloy XK360 developed by Mercury the anode is pure aluminium.

 

[QBhoy]

Hi.

Just thought i would chip in. The merc “aluminium” anode technically isn’t quite pure Aluminium. It’s of an alloy make up and towards a more sacrificial make up than the obviously aluminium drive it’s attached to.

 

[Fishtigua]

Merc outdrives are treated in a ceramic coating to stop corrosion too, for added protection.

 

[vas]

Merc outdrives are treated in a ceramic coating to stop corrosion too, for added protection.

View attachment 77109

FFS!
how many decades has this boat being in the water???

leg looks like it needs new seals

they should really step down the jet pressure on the cleaner though...

V.

 

[Dog's dinner]

Hi,
Just an update on my aluminium anodes this year. After last years total loss.
After 9 months back in water all the anodes seem as normal with the exception of the Port side trim tab anode which appears to have broken up with a brown staining around it.
It looks like rust I am just wondering if we spaced that anode off the trim tab using a steel washer.
Unlikely as we use the same ones every year, we will see when lift out this year.

 

[sailorman]

I recently learned, based on some documentation from a couple of anodes producers, that there are anodes made of an aluminum alloy which are allegedly better than the traditional zinc ones in just about every way (strictly talking of sea water):

- more longlasting, while offering the same level of protection if not a tad better;
- significantly lighter - about half the weight of equivalent zinc anodes - obviously an advantage particularly on moving parts like rudders and shafts;
- slightly cheaper - though the price difference is nowhere near enough to be relevant for the comparison.

Now, I am ordering zinc anodes at the moment, on the "if it ain't broken, etc." basis.
But the above got me thinking, because it sounds too good to be true - to the point of wondering why zinc anodes are still produced at all.

So, I thought to check the forum consensus, if any.
Wadduthink, folks?

Seawater zinc freshwater alloy