Waterjet anodes in freshwater, magnesium not available

[DHV90]

I have a pair of waterjets on a boat kept in freshwater, most of the external anodes are a simple shape and probably easy to find something off the shelf made of Mag to replace them with, but they have an internal ring anode which is only available in Ally or Zinc, and probably impossible to find anything to replace it with short of having something custom made.

Hoping for a bit of input and some opinions on what would be best to do please!

The Ally anodes have worn very little in 3 years, but the boat is far from any stray currents and there is no corrosion on the jet units yet.

Am I best replacing as much as I can with magnesium, and leaving anything unobtainable with Ally? will any benefit the ally anode had before be negated by having magnesium outside the unit 'protecting' the ally anode, and risk corrosion on the internal surfaces?

Would I be best to keep everything the same material and regularly inspect for any signs of corrosion?

or just go and have some custom anodes made in Mag?

Thanks in advance

 

[Greg2]

I wou,d have thought keeping the same material is preferable as the weakest will corrode first. Ali works in fresh and salt so I would go with that. FWIW we are moored in fresh and cruise booth fresh and salt and have used Ali for years.

 

[kashurst]

better to keep them all the same material, otherwise the most reactive will act as the sacrificial anodes and the others won't do much. Saying that in fresh water they won't do much anyway. i.e. will last a long time

 

[Momac]

I use aluminium anodes in fresh water (mostly)
No problems with corrosion.
I agree don't mix the anode metals if at all possible.