Aluminium v zinc anodes?

[philipm]

I've kept my boat on freshwater for the first year of its ownership (magnesium anodes) but going to move to the coast and suddenly faced with the above dilemma. Have done a bit of reading and can't find much wrong with aluminium apart from a suggestion it doesn't "slough" any coating on it if the boat is not used regularly.

Any strong recommendations on aluminium or zinc from more experienced boaters out there??

 

[Andyroonot]

The new VP DPI drive only has aluminium or magnesium anode options, no zinc.

Appreciate that possibly doesn’t answer your question but if VP are moving away from zinc then they obviously feel that aluminium offers sufficient protection for saltwater boating installations

 

[MrB]

This subject was covered on here not to long ago (months) and iirc aluminium was starting to be favored. It's worth a search.

 

[rafiki_]

Normally magnesium for freshwater, aluminium for brackish and zinc for sea water.

 

[Murv]

I was convinced to switch to aluminium a couple of years ago, have just renewed with aluminium again.

 

[ctva]

Best to ask what your new neighbours use as different locations seam to favour certain types. All a bit of strange alchemy.

I too am contemplating switching from zinc to alu but as the zinc has worked flawlessly for 15 years so probably not.

My situation is fresh Crinan Canal water and salt water, and the zinc just works despite what all the books say.

 

[PeterBoater]

Normally magnesium for freshwater, aluminium for brackish and zinc for sea water.

Modern thinking is aluminium for both brackish and salt. At least one thruster manufacturer only does aluminium anodes. A small side effect of buying anodes by mail order is that aluminium is much cheaper for P&P.

 

[Momac]

I keep my boat on fresh water with occasional backish and salt water trips. Typically 2 to 3 weeks continuously on salt water each year for our main holiday voyage.
The aluminium anodes comfortably last 2 years. They might last longer but I change them regardless.
My bow thruster anode is available only in zinc. That doesn't seem to be an issue.

 

[philipm]

I keep my boat on fresh water with occasional backish and salt water trips. Typically 2 to 3 weeks continuously on salt water each year for our main holiday voyage.
The aluminium anodes comfortably last 2 years. They might last longer but I change them regardless.
My bow thruster anode is available only in zinc. That doesn't seem to be an issue.

I'll be on salt water full time. Interesting to read your comment regardless.

I wonder if all bow thrusters have anodes. I don't recall anyone mentioning that when I bought it from the dealer and I'm a relative newbie.

 

[philipm]

The new VP DPI drive only has aluminium or magnesium anode options, no zinc.

Appreciate that possibly doesn’t answer your question but if VP are moving away from zinc then they obviously feel that aluminium offers sufficient protection for saltwater boating installations

Yes that's a strong vote of confidence from VP (the conspiracy theory being aluminium is cheaper so maybe they're trying to keep costs down - but I doubt it).

 

[swatkins]

Switched to Aluminium (brackish water) does exactly the same job in terms of corrosion over two years and they are cheaper!

 

[Bouba]

This slough off business is worrying. If the aluminium doesn’t self clean then it will get completely covered in slime and be sealed thus not working. The good news is that it will last a long time

 

[Momac]

This slough off business is worrying. If the aluminium doesn’t self clean then it will get completely covered in slime and be sealed thus not working. The good news is that it will last a long time

Aluminium anodes seem to work for me.
The anodes corrode. The outdrives don't.

After 2 years the anodes looked okay but on closer examination in fact they had lost a fair bit of weight .

 

[tico]

Aluminium worked better for me in Brackish/salt water than Zinc. The Zinc ones always got a hard white coating of oxide which reduced their effectiveness. Ally ones lasted 12 months, but needed replacing after that.

 

[About Time]

I am in light salt water and tested aluminium … it did not work for me. Salinity content in my water is ard. 29/30... As far as I can see this level of salt is considered between brackish and salt water. Zinc works much better for me in this kind of water. I for sure will agree on the old terms: fresh requires magnesium and salt requires zinc but when speaking brackish you need testing. Aluminium may be best option here but not always.

 

[Greg2]

I am in light salt water and tested aluminium … it did not work for me. Salinity content in my water is ard. 29/30... As far as I can see this level of salt is considered between brackish and salt water. Zinc works much better for me in this kind of water. I for sure will agree on the old terms: fresh requires magnesium and salt requires zinc but when speaking brackish you need testing. Aluminium may be best option here but not always.

Interesting. Been using Alu on various boats in both salt and fresh and they have worked just fine for us.