Zinc or Magnesium Anode?

[Limecc]

Disregarding cost or availability, supposing your engine hours are spent running 50% freshwater, 50% saltwater, would you opt for zinc anodes or magnesium anodes?

Also I saw some labelled 'aluminium' anodes? What's the point when the engine is made from aluminium?

[GuyC]

There does seem to be a move towards aluminium anodes from zinc ones and I'm always slightly sceptical about whether an aluminium anode can protect an aluminium stern drive / outboard. MG Duff do recommend aluminium for many stern drives and I'm sure would recommend something to you if you asked them.

The salt water to fresh water is an issue. The recommendation is that if you are spending prolonged periods in either, you should change your anodes to suit.

[beamishken]

Originally Posted by Limecc

Disregarding cost or availability, supposing your engine hours are spent running 50% freshwater, 50% saltwater, would you opt for zinc anodes or magnesium anodes?

Also I saw some labelled 'aluminium' anodes? What's the point when the engine is made from aluminium?

Certain manufacturers have gone away from zinc anodes to aluminium however it is a less noble grade than that of the material its intended to protect hence they do work.
Aluminium is what I use & you will be fine with aluminium

[babbot1]

I also wondered how it would work protecting Aluminum parts but like mentioned above the anode is a cheaper grade and will degrade first. I also use aluminum being in both environments.

Location is also a factor. Water temp and salinity will also change the degradation so check often during the season. Aluminum will degrade quicker than zinc in salt. So if it's your first year switching from zinc to al then keep an eye on them.

Magnesium is only for fresh. It will degrade super fast in salt.
Zinc is only for salt. It will not degrade fast enough or at all in freshwater.
Aluminum is the go to for being in both environments.

[beamishken]

My understanding is the reason for the switch to aluminium from zinc is because it degrades slower therefore provides protection for longer its also suitable for fresh or saltwater use which is ideal for the ops purpose

[mikehhogg]

Magnesium anodes are normally used on steel vessels used in fresh water,
Zinc was the preferred anode for salt water use .Zinc will coat with a whitish deposit in fresh water and will need to be wire brushed before it will be effective in salt water again. Aluminium anodes are not 100 percent aluminium they are alloys There are a lot of other factors to take into consideration as in the boat hull material, prop and stern material ,how long you spend in a particular location and whether you tie up in a marina. I could safely say that most corrosion will take place in Marinas .

[Limecc]

Thanks chaps, based on your replies I ordered 3 Suzuki engine anodes in aluminium, shame I already purchased a complete set of new zincs. Therefore I'm going to leave the external anodes in zinc I think. We probably do 2/3 of our boating in fresh water, the rest in salt.

This is a comparison old vs new after 14 years (dry docked, only 218hrs) salt water use, never checked/changed by previous owners.