Best anodes for sea water: zinc or aluminum

[Fishtigua]

But according to some anodes producers, alu is as good as zinc also in salt water.

Just as an aside, has anyone checked with the likes of Volvo, CAT or MTU which they prefer in their engines?

 

[VicS]

Hi
Pretty definitively;
Zinc are for sea water
Magnesium are for fresh water
Aluminium are for brackish or a mix of both and are also what the OEM will play it safe with, as in with merc and VP outdrives. They will not offer the same protection as a zinc in SW, for certain.

Aluminium anodes have a slightly more negative electrode potential than zinc anodes. In theory , therefore, they offer slightly more protection.

 

[oldgit]

Invicta Anodes.
300mm x 87 x 45mm.

Zinc. £31.00. +VAT
Matching anode in Alu. £22.00 +VAT

 

[NBs]

Tecnoseal anodes (zinc version) is what I used last season, and they worked brilliantly. I suppose the version you are referring to is the alu ones, whose part numbers in their catalogue ends with "AL" (as opposed to no letters for zinc, and "MG" for magnesium).
I'm not sure if Tecnoseal managed to get any patent on their own alu alloy, but pretty sure they are not alone in offering alu anodes.
"Alu" always meaning a special alloy of course, obviously different from any structural alu parts used in outdrives or whatever.
Anyway, fwiw, material aside, here in IT Tecnoseal stuff is considered the best, and I don't think you will get wrong with that.
I will be interested to hear about your experience!

Hi

Sorry, No tecnoseal, my new anode brand is https://performancemetals.com/ and marketing say:

"The Only Anode That Works in All Types of Water

The aluminum alloy used in Navalloy anodes is very different from normal aluminum. It includes about 5% zinc and a trace of Indium, which prevents the build up of an oxide layer.

Aluminum anode alloy provides more protection and lasts longer than zinc. It will continue to work in freshwater and is safe for use in salt water. Aluminum is the only anode that is safe for all applications.

Better Protection

Navalloy® has a higher protection voltage than zinc.

Longer Life

Navalloy® lasts up to 30-50% longer than zinc."

And more this Navalloy anodes
https://cdn.shopify.com/s/files/1/2245/5025/files/Navalloy_Anodes_Flyer_May14.pdf

NBs

 

[Portofino]

Island if Ireland has a distinct northern part belonging to the U.K. or just Ireland ?

Nomenclature guys

Aluminium or an Alloy as said in post above ?
I don,t think there’s such a thing as an Aluminium anode , that’s an anode made of Aluminium with zero deliberate additives .

View attachment 75754

Aluminium is LESS noble than 99.9% Zinc and thus its proctective currernt is lower .
However making an alloy with other metals may give a marginal slight increased voltage , but above a certain V if you go too high you may end up protecting your neighbors boat(s) anyhow .

Zinc is the go to for seawater on a shaft drive more so if that seawater is more salty - Er like the Med .

Zinc with [ insert your metal % ] will deplete less and last longer .
Your aluminium ALLOYs like the one NB quote s have zinc in a smaller concentrations hance the longevity.
The base bulk substance of AL gives off a lower current, it’s its additives use of other metals inc some zinc that slightly inc the V .

Protection Vs depletion

If it ain’t depleting it’s not working !

You want it the anode to deplete not your sterngear corrode - right ?

With a Med based boat the depletion rate is easy to manage with 99.9 % Zinc , you can easily either snorkel or better with a bottle dive .

I’ve replaced prop anodes in Oct and happpy to do so to make sure it’s ok sitting in the marina over the closed season .
I replace when 1/2 worn not necessary at the annual lift .

Just want what’s best in terms of protection.

Caking your hull with copper coat is huge source of potential problems that could upset a nice protective equilibrium ( 99.9%zinc or an alloy mostly of AL ) not be ignored.An unnecessary layer ( scuse the pun ) of complications .

 

[Bouba]

Does anyone know if the crud layer on a zinc affects the efficacy?

 

[Portofino]

Does anyone know if the crud layer on a zinc affects the efficacy?

It does you are supposed to knock if off periodically.
Depends where the anodes are .If in the water stream say a shaft or under a flap the “ crud” will naturally clear with fwd motion ,esp at 30 knots cruise

How ever out of the water steam like transom anodes it will not wash off .
It’s a surface area thingy ,you need max area , the crud is an oxide that decreases the S.A.

However now you have raised the issue that’s actually a major problem with the AL alloys like the ones NB above has linked , The oxide or crud forms quite an adherent layer if the boats static thus significantly reducing the S.A. and any imho any perceived or real advantage over zinc .
That’s the main reason theses alloys last , Its cos there oxide is not like Zinc crude its a almost invisible film wrapping the thing up

Remember
Depletion Vs protection .

 

[Portofino]

The problem we have here is the difference between
In vitro and in vivo .

Taking on board Jrudges comment ( can,t be arsed googling the word )

Vitro is glass , in the lab in a test tube or similar scenario whereby the voltage of a new alloy of AL gives all the right results .So they publish correct and accurate information and the marketing guys use that .

Vivo is In the body , in this case on your boat .
The vitro results fail to take into account the oxide layers and ease or not in the case of Al alloys there removal .Or turned around the significance of the surface area reduction in real LIFE scenarios .

 

[NBs]

Hi,

I'm thinking this white fragile "oxide" due to low salt sea. Brush and lick all the zincs a couple of times in the season, also all the anodes of the heat exchanger. I do not know whether this is useless or whether electricity passes through this brittle "oxide", so try to look at the conductivity of the electricity with a multimeter.

NBs

 

[BruceK]

Does anyone know if the crud layer on a zinc affects the efficacy?

Yes. It nullifies it

 

[BruceK]

Island if Ireland has a distinct northern part belonging to the U.K. or just Ireland ?

Nomenclature guys

Aluminium or an Alloy as said in post above ?
I don,t think there’s such a thing as an Aluminium anode , that’s an anode made of Aluminium with zero deliberate additives .

View attachment 75754

Aluminium is LESS noble than 99.9% Zinc and thus its proctective currernt is lower .
However making an alloy with other metals may give a marginal slight increased voltage , but above a certain V if you go too high you may end up protecting your neighbors boat(s) anyhow .

Zinc is the go to for seawater on a shaft drive more so if that seawater is more salty - Er like the Med .

Zinc with [ insert your metal % ] will deplete less and last longer .
Your aluminium ALLOYs like the one NB quote s have zinc in a smaller concentrations hance the longevity.
The base bulk substance of AL gives off a lower current, it’s its additives use of other metals inc some zinc that slightly inc the V .

Protection Vs depletion

If it ain’t depleting it’s not working !

You want it the anode to deplete not your sterngear corrode - right ?

With a Med based boat the depletion rate is easy to manage with 99.9 % Zinc , you can easily either snorkel or better with a bottle dive .

I’ve replaced prop anodes in Oct and happpy to do so to make sure it’s ok sitting in the marina over the closed season .
I replace when 1/2 worn not necessary at the annual lift .

Just want what’s best in terms of protection.

Caking your hull with copper coat is huge source of potential problems that could upset a nice protective equilibrium ( 99.9%zinc or an alloy mostly of AL ) not be ignored.An unnecessary layer ( scuse the pun ) of complications .

'aluminium' anodes are an alloy of Al, Zn and Indium so not 'just' Al.

 

[MapisM]

You have the added worry of balancing the electrochemical effects of your copper coat with your anodic protection. Good luck with that .As said before I fail to understand how in one breath the copper is wrapped up in resin thus rendered inert and in the other it’s constantly exposed to give antifoul properties? Huh !

Caking your hull with copper coat is huge source of potential problems that could upset a nice protective equilibrium ( 99.9%zinc or an alloy mostly of AL ) not be ignored.An unnecessary layer ( scuse the pun ) of complications.

Sorry, I forgot to reply to your previous comment above, and I was reminded by the second one in your last post.

It's actually a bit o/t in this thread, but I guess the subject might be of interest also for someone else who is considering CC, so here's my 2c.
First of all, I read all sort of things about CC interference (or lack of, depending on sources) with anodic protection, so I believe it's impossible to reach a generally valid conclusion.
My gut feeling is that, among other factors, a good bonding system is relevant.
And before deciding to give CC a try, I knew that this was the last of my concerns, having oversized cables and very strong connections everywhere.
But I must admit that in principle I see your point ref. the inconsistency between the copper either "wrapped up in resin", therefore insulated, or exposed to be effective as a/f. I have no explanation for that.

What I can say, based on my first hand (albeit admittedly rather short) experience, is as follows:
1) in season 2017, the new to me boat was NOT yet coppercoated, and before launch she was antifouled "normally" and had all anodes replaced (zinc).
2) before re-launching her in 2018, the hull was sanded and CC-ed. Anodes were again replaced with zinc ones.

Now, after lifting her at the end of season 2018, if there was any difference in the way anodes worked, I don't have the slightest idea of what it was.
I mean, zero, zilch, nothing.
It's a pity that I didn't keep the old anodes for a comparison, but I'm 99.9% sure that it would have been impossible to tell which is which, even putting the 2017 and 2018 anodes side by side.

Just for sake of accuracy, aside from the hull difference (traditional a/f vs. CC), the two seasons were not 100% comparable, because in the latter the boat crunched many more miles, spent some more time in the water, and was moored in several different places.
So, of course I'm not pretending that the identical anodes behavior is a scientific proof that CC is irrelevant.
In a sense, it would have been reasonable to expect a bit more anodes wear in 2018, but they clearly did work, that's for sure.
Which is much more reassuring than lifting the boat and find out (as someone say that can happen with CC!) that all the u/w gear is falling apart, anyway...

 

[Portofino]

It’s not so much comparable wear rates of zinc pre and post CC , although interesting it the protection of the stern gear.
With the copper abundance there’s a chance it’s masking the lower protection.
You need to get a quantitative measurement of the surface or other bits of the stern gear .

I can’t figure it out the exact affect ( agreed if any ? ) of CC ,on anodic protection .
Seems to work with conventional Zinc .

There will be some interaction , but what beneficial or detrimental?

 

[MapisM]

You need to get a quantitative measurement of the surface or other bits of the stern gear.

That's unlikely to be ever included in my "to dos" list, PF...

 

[TheOrs]

I can’t figure it out the exact affect ( agreed if any ? ) of CC ,on anodic protection .

I don't think the CopperCoat will make any difference because the flakes of copper are not connected to each other or to the bonding system.

The copper is encapsulated in resin and must be exposed to work but I believe (& I'm happy to be told I'm wrong ) that each piece of copper is insulated from the next by the resin; so no circuit is made.
i.e if you take a CopperCoated hull and stick a meter across two exposed pieces of copper you should see open circuit.

 

[Portofino]

I don't think the CopperCoat will make any difference because the flakes of copper are not connected to each other or to the bonding system.

The copper is encapsulated in resin and must be exposed to work but I believe (& I'm happy to be told I'm wrong ) that each piece of copper is insulated from the next by the resin; so no circuit is made.
i.e if you take a CopperCoated hull and stick a meter across two exposed pieces of copper you should see open circuit.

I,am righty’s or wrongly coming from the other direction .
The anodes degrade dissolve away in the electrolyte ( seasalts of different concentration-Med being particular at the high end of the scale ) .
They release subatomic particles that protect the sterngear like a stainless shaft or nibral prop or alloy flap or bronze skin fitting .Any electrical currents ,there voltages are a by product of the protection .
It’s the relative movement of the subatomic particles from the anode in the salt solution easier to the stuff that you want to protect .

Cooper ions and cooper salts ,fresh cooper exposed might detrimentally interfere with that protection ?

Copper to copper may show zero voltage , but I,am thinking the copper may lower the concentration of the good subatomic particles released from the anodes ,to the metals listed above they are trying to protect .
Somehow interfer with the efficacy of the anodes .

I think in pure water H2O , ie zero salts in solution you don,t need any anodes , as soon as you start adding / dissolving salts that easily ionise like sodium and a bunch of others to make seawater the more concentrated adding dissolved metal salt solutions the more electrochemical active solution becomes .

If you take copper pipes that are soldered the old way ( before plastic pushfits ) after say 30 years the solder eats ,corrodes through the copper and the joint springs a leak or weeps , you see the green copper oxide .In theory the joint supposed to inert but the cooper corrodes through .

I just can’t see CC being inert , invisible to the subatomic particles released from the anodes , both types in a concentrated salt solution .
Only metals like gold , palladium etc attached to your hull will be inert , I can buy that.

 

[Dog's dinner]

Problem / mystery with my aluminium anodes.
I have been using aluminium anodes on my boat for 5 yrs now.
1 x 140mm x 0.800KG on hull bonded to everything.
2 x 100mm x 0.380kg each on trim tabs.
4 x 60mm x0.095kg each on stainless rudders.
The anodes have all been purchased from the same manufacturer over these years.
And have been from mixed batches.
I have contacted the manufacturer and questioned whether the mix has changed and he says no its always been the same.
They have been making them for 20yrs.

The boat stays in the water for a whole year and the anodes come out usually 3/4 gone.
I scrub the anodes off every month or so from pontoon.
Last year annual lift boat out in August big shock all anodes virtually gone.
I check all the anodes are earthed to each other and the 2 Bronze props every relaunch.
I have also got an galvanic isolator with DC and AC leakage warning lights which I have tested and confirmed working with the manufacturers.
I had an marine electrician out to check the boat/ anodes to the sea water on the berth when she went back in in August, he had a special meter for it and said it was all good.
Now this year when I go to clean the scale/ muck off the anodes with my extended loo brush I have noticed there is also an opaque Jelly type substance coming off them it is in blob shapes almost like its oozing or growing out of them.
This I have not seen before.
Has anyone any Ideas what this can be. ?

 

[Wavey]

I switched to aluminium last autum based on recommendations from a couple of friends and a fellow Broom owner based in Lymington who has used ali for years. They were supplied by a company in Kent who mainly supplies commercial outfits but I spoke at length with them before ordering and they certainly seemed to know their stuff.

The proof of the pudding will be next month when my boat is lifted for antifouling. It will be interesting to see how they look.

 

[sap_2000]

I find these charts from boatzincs.com very informative.

https://www.boatzincs.com/pdfs/Chart_A-Which_Anodes_Should_I_Use.pdf

 

[Dog's dinner]

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 ?