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Re: Propeller pitting
Agree with the others .....
First consideration is to return to the usage of a Zn anode.
Such logic can be easily validated by checking with what most other boats in your location are successfully using. As regards the usage of Mg instead of Zn ... the acidity/alkalinity of the water is also a controlling factor in anode selection; seawater is generally slightly alkaline; fresh water is usually slightly acidic ... but not always and especially on the western side of the US depending on location (proximity to deserts, active mining or paper mills, etc. etc).
Another consideration could be: has the nature of the fouling attached to your and other adjacent boats severely changed from the recent past. Reason: attached various microorganisms, bacteria especially, can use certain microscopic (alloy) 'grains' of underwater metals as their nutrient source; thus, such pitting can be due to 'biology'. But, other adjacent boats would also have such a developed condition in their underwater running gear.
If you had an electrical leak from your bilge pump switch, or a high resistance through your engine bonding/ground connection, or a 'shared' electrical leak through your marina's AC 'ground' system, that Mg anode would probably show this, and your Mg anode looks to be relatively 'unused'.
Rx: Id imitate what the other boats in your venue are (successfully) using, as the use of Mg anodes may be entirely inappropriate due to the 'local' water chemistry and its acid/alkaline balance (pH).
Last edited by RichH; 12-11-2016 at 11:30 AM.