Anodes

[Bigplumbs]

I have a sports cruiser with an Alpha one Gen 2 leg. The boat was in the sea in the UK on a mooring from Late April to mid October (so almost 6 months). I bought a new set of anodes but the ones on the leg look hardly eroded at all. I am going to take them off, weigh each one and compare it with the new ones.

How many years do your anodes usually last. I don't know what the current ones on the leg are made of but the boat was dry stacked and used on the sea so no real anode corrosion would have been previously expected.

The new ones I bought are AL (Aluminum) Mil-spec A-24779 (SH) and are supposed to be for salt water

Dennis

 

[rafiki_]

Normally zinc anodes are for sea use. I would be surprised if they last more than 1 season. They have a lot of aluminium to protect with the leg.

 

[gjgm]

What is your prop? Aluminium? Check you have seawater anodes as has been mentioned...but it varies year to year,location to location. My prop anodes against stainless steel get munched but others against the leg last a couple of seasons plus

 

[Bigplumbs]

My Prop is Ali. AAlso when I researched the anodes the new ones I got are supposed to be for salt water. Not sure what the ones already on are though

 

[TheOrs]

Lots of 'depends' here:

Where is it moored? How much tidal flow? Do you have a MerCathode? Do you have a stainless or aluminium prop? Is the paint on the leg in good condition?

I wouldn't worry about the anodes being aluminium, the Merc anodes are usually ally.

 

[Bigplumbs]

See this is what confuses me. I bought these

http://www.tcschandlery.co.uk/tecno...MaxGNuvj-O03GBisd8Rd-x5F7JIb5c1CKDhoCHQvw_wcB

which are Aluminium and say for salt and brackish water

But these are Zinc and say for salt water

https://www.asap-supplies.com/mgduf...lGWPnnkdj0BQnB5G17yEr5i9_Y7K19lMuuRoCeZHw_wcB

Who is correct

 

[GrahamHR]

See this is what confuses me. I bought these

http://www.tcschandlery.co.uk/tecno...MaxGNuvj-O03GBisd8Rd-x5F7JIb5c1CKDhoCHQvw_wcB

which are Aluminium and say for salt and brackish water

But these are Zinc and say for salt water

https://www.asap-supplies.com/mgduf...lGWPnnkdj0BQnB5G17yEr5i9_Y7K19lMuuRoCeZHw_wcB

Who is correct

I was very sceptical about "aluminium" anodes for salt water use until a well reasoned electrochemical explanation on here as to why they could be better than zinc ones. I bought some, they work better than the zinc ones do in protecting the aluminium alloy outdrive parts. I'm a convert. They are not of course pure aluminium. but an alloy designed with the correct electrode potential to be able to protect the outdrive.

You need to ensure electrical continuity between the anodes and all alloy pars of the outdrive

I know very little about Mercury drives and props. For Volvos I have experience of, DPS and DPH drives, the props are not electrically connected to the drive or anodes on the drive so their stainless or nibral props do not, cannot, affect anode wear rates.

As a precaution I recommend the Mercathode or Volvo ACP equivalent.

 

[rafiki_]

See this is what confuses me. I bought these

http://www.tcschandlery.co.uk/tecno...MaxGNuvj-O03GBisd8Rd-x5F7JIb5c1CKDhoCHQvw_wcB

which are Aluminium and say for salt and brackish water

But these are Zinc and say for salt water

https://www.asap-supplies.com/mgduf...lGWPnnkdj0BQnB5G17yEr5i9_Y7K19lMuuRoCeZHw_wcB

Who is correct

The normal anode selection is:

Magnesium for freshwater
Aluminium for brackish
Zinc for seawater.

 

[QBhoy]

Rafiki is spot on here.
Al anodes are defo for a salt/fresh mix. Should be zinc for your application.
Your particular leg is succeptable to corrosion at the power trim fittings on the side of the ram and can be a real pain in the bum if left unchecked.
Without checking, I'd imagine al would be the worst possible anodes for your application. In fact I'd go so far as to say they shouldn't be used, no matter what.
Either magnesium or zinc and nothing else.
Zinc would be recommended for your use.
From memory, magnesium, zinc then aluminium would be the order of sacrificial effect. To me aluminium is a lazy way out, in terms of anode use. Sure, they will last for ages, but if they aren't eroding.....what else is instead ?
Just my thoughts....

 

[GrahamHR]

Rafiki is spot on here.
Al anodes are defo for a salt/fresh mix. Should be zinc for your application.
Your particular leg is succeptable to corrosion at the power trim fittings on the side of the ram and can be a real pain in the bum if left unchecked.
Without checking, I'd imagine al would be the worst possible anodes for your application. In fact I'd go so far as to say they shouldn't be used, no matter what.
Either magnesium or zinc and nothing else.
Zinc would be recommended for your use.
From memory, magnesium, zinc then aluminium would be the order of sacrificial effect. To me aluminium is a lazy way out, in terms of anode use. Sure, they will last for ages, but if they aren't eroding.....what else is instead ?
Just my thoughts....

I give up, I just can't be bothered anymore.

So;

Stainless props do eat anodes even they are not electrically connected to them ( magic or hearsay, we all know those facts are real)

Aluminium anodes are of course useless in salt water

 

[TheOrs]

Your particular leg is succeptable to corrosion at the power trim fittings on the side of the ram

If this is happening it's probably because the continuity wires are broken or missing (they are quite fragile)

From memory, magnesium, zinc then aluminium would be the order of sacrificial effect.

It's Magnesium, Aluminium then Zinc in order of decreasing reactivity.

To me aluminium is a lazy way out, in terms of anode use. Sure, they will last for ages, but if they aren't eroding.....what else is instead ?

Zinc will last longer than Aluminium which will last longer than Magnesium. If you have scratches in the paint on your leg you will have exposed aluminium. This will corrode away as the zinc will not protect it. Rather; your aluminium leg will be protecting the zinc anode (ish - they are all alloys, so not quite as simple as that!)

The standard , OEM anode kit for an Alpha One, Gen 2 is 888756Q03. This is what they fit from the factory & what I use.

Also, do not mix anode materials. When I got my boat it had Ally on the leg and zinc on the tabs. The zinc were doing nothing as they were being protected by the leg anodes which wore quicker as a result.

 

[QBhoy]

The ors
Are you certain about your order of corrosion ?
I'd be surprised in aluminium was placed above magnesium or zinc.
With regards to the corrosion point I mentioned, it is simply an observation over the years and been identified as a weak point in my experience. That said, there was a case locally a few years back where the main cause of this was from the marina pontoons not being earthed properly (from memory) and causing a reaction on this part. The local mercury dealer did really well out of this !!
With regards to the factory fit ALU anodes, this is surely just a safe move from a large corporate company to avoid any likely liability ?

 

[QBhoy]

Hi there,
I've just checked a few galvanic scales there. Have a look for yourself theorrs.
prerty sure I am correct.

 

[Bigplumbs]

So still more confusion. I cant see any problem with my leg and the continuity wires seem good. I am going to stick with the anodes I have purchased

Dennis

 

[Bigplumbs]

I just did a search on McDuff website and they recommend what I have purchased so I am now happy

http://mgduff.co.uk/yachts-and-powe...facturer/mercury--mercruiser-kits/cmalphakita

Dennis

 

[rafiki_]

Stainless props do eat anodes even they are not electrically connected to them ( magic or hearsay, we all know those facts are real)

Aluminium anodes are of course useless in salt water

It is not Stainless Props that eat anodes, it is the galvanic currents, connecting metal to metal, unless you give the currents an easier path. Unless you meant something else?

 

[TheOrs]

Hi there,
I've just checked a few galvanic scales there. Have a look for yourself theorrs.
prerty sure I am correct.

Yes, I see what you are saying about the galvanic series. I am going by the fact that the galvanic series generally shows a rating for aluminium alloys not pure aluminium.

My understanding is that magnesium reacts most hence fresh water use, zinc reacts least, hence saltwater and aluminium is somewhere in between. This ties in with personal experience where my aluminium anodes dissolved within three months but the zincs next to them were hardly touched.

I am happy to accept that I may be wrong though. ??

 

[rafiki_]

Yes, I see what you are saying about the galvanic series. I am going by the fact that the galvanic series generally shows a rating for aluminium alloys not pure aluminium.

My understanding is that magnesium reacts most hence fresh water use, zinc reacts least, hence saltwater and aluminium is somewhere in between. This ties in with personal experience where my aluminium anodes dissolved within three months but the zincs next to them were hardly touched.

I am happy to accept that I may be wrong though. ����

You are spot on. ��

 

[VicS]

I have a sports cruiser with an Alpha one Gen 2 leg. The boat was in the sea in the UK on a mooring from Late April to mid October (so almost 6 months). I bought a new set of anodes but the ones on the leg look hardly eroded at all. I am going to take them off, weigh each one and compare it with the new ones.

How many years do your anodes usually last. I don't know what the current ones on the leg are made of but the boat was dry stacked and used on the sea so no real anode corrosion would have been previously expected.

The new ones I bought are AL (Aluminum) Mil-spec A-24779 (SH) and are supposed to be for salt water

Dennis

If the old anodes are zinc but the same size as your new aluminium anodes they will be much heavier ( more that 2½ times)

Zinc or aluminium anodes are suitable for seawater use. Aluminium is also suitable for brackish water

 

[VicS]

See this is what confuses me. I bought these

http://www.tcschandlery.co.uk/tecno...MaxGNuvj-O03GBisd8Rd-x5F7JIb5c1CKDhoCHQvw_wcB

which are Aluminium and say for salt and brackish water

But these are Zinc and say for salt water

https://www.asap-supplies.com/mgduf...lGWPnnkdj0BQnB5G17yEr5i9_Y7K19lMuuRoCeZHw_wcB

Who is correct

They are both correct. Aluminium anodes are sutaible for both salt and brackish waters

Zinc is only suitable for salt water because in brackish water ( and fresh water) it becomes passivated by an oxide layer

The normal anode selection is:

Magnesium for freshwater
Aluminium for brackish
Zinc for seawater.

Aluminium anodes are also suitable for seawater

Rafiki is spot on here.
Al anodes are defo for a salt/fresh mix. Should be zinc for your application.
Your particular leg is succeptable to corrosion at the power trim fittings on the side of the ram and can be a real pain in the bum if left unchecked.
Without checking, I'd imagine al would be the worst possible anodes for your application. In fact I'd go so far as to say they shouldn't be used, no matter what.
Either magnesium or zinc and nothing else.
Zinc would be recommended for your use.
From memory, magnesium, zinc then aluminium would be the order of sacrificial effect. To me aluminium is a lazy way out, in terms of anode use. Sure, they will last for ages, but if they aren't eroding.....what else is instead ?
Just my thoughts....

Rafki is wrong I am afraid! Aluminium anodes can be used in seawater.

The alloy from which "aluminium" anodes are made is slightly more anodic than zinc . In the situation you describe aluminium anodes may well, therefore, be slightly more effective than zinc anodes

I give up, I just can't be bothered anymore.

Head against brick wall !

It's Magnesium, Aluminium then Zinc in order of decreasing reactivity.

Zinc will last longer than Aluminium which will last longer than Magnesium. If you have scratches in the paint on your leg you will have exposed aluminium. This will corrode away as the zinc will not protect it. Rather; your aluminium leg will be protecting the zinc anode (ish - they are all alloys, so not quite as simple as that!)

The standard , OEM anode kit for an Alpha One, Gen 2 is 888756Q03. This is what they fit from the factory & what I use.

Also, do not mix anode materials. When I got my boat it had Ally on the leg and zinc on the tabs. The zinc were doing nothing as they were being protected by the leg anodes which wore quicker as a result.

The order of decreasing reactivity is magnesium, aluminium anodes, zinc, aluminium and other aluminium alloys. Magnesium is by far the most reactive which is why it is unsuitable in brackish or salt water. Aluminium anodes are slightly more reactive (anodic) than zinc anodes ( - 1.09 volts compared with - 1.05 volts). Zinc anodes are a little more reactive than aluminium and other aluminum alloys.

Zinc anodes will protect the aluminium leg..... aluminium anodes will protect it more effectively

The ors
Are you certain about your order of corrosion ?
I'd be surprised in aluminium was placed above magnesium or zinc.
With regards to the corrosion point I mentioned, it is simply an observation over the years and been identified as a weak point in my experience. That said, there was a case locally a few years back where the main cause of this was from the marina pontoons not being earthed properly (from memory) and causing a reaction on this part. The local mercury dealer did really well out of this !!
With regards to the factory fit ALU anodes, this is surely just a safe move from a large corporate company to avoid any likely liability ?

Hi there,
I've just checked a few galvanic scales there. Have a look for yourself theorrs.
prerty sure I am correct.

magnesium .............. - 1.60 to - 1.63 volts
aluminium anodes..... -1.09 to -1.10 volts
zinc ...........................- 0.98 to - 1.03 volts
aluminium and other aluminum alloys ....... - 0.76 to - 1.00 volts

So still more confusion. I cant see any problem with my leg and the continuity wires seem good. I am going to stick with the anodes I have purchased

Dennis

I just did a search on McDuff website and they recommend what I have purchased so I am now happy

http://mgduff.co.uk/yachts-and-powe...facturer/mercury--mercruiser-kits/cmalphakita

Dennis

Sensible but see my foot note to this post.

Yes, I see what you are saying about the galvanic series. I am going by the fact that the galvanic series generally shows a rating for aluminium alloys not pure aluminium.

My understanding is that magnesium reacts most hence fresh water use, zinc reacts least, hence saltwater and aluminium is somewhere in between. This ties in with personal experience where my aluminium anodes dissolved within three months but the zincs next to them were hardly touched.

I am happy to accept that I may be wrong though. ??

the aluminium / zinc/ indium alloy from which so called aluminium anodes is made is slightly more anodic ( reactive ) than zinc. Most other aluminium alloys are slightly less reactive than zinc and can therefore be protected by zinc anodes

FOOTNOTES

Zinc anodes are made of a high purity zinc with only small percentages of alloying elements and strict limits on impurities. Notably the iron content must be very low.

Aluminium is very much less dense than zinc therefore aluminium anodes are much lighter than zinc anodes of the same physical size. They will therefore appear to be consumed much more quickly simply because there is less mass present. Be particularly vigilant when replacing zinc anodes with aluminium ones. Dont assume they will last as long. They wont.