Revelations about zinc electrodes.

Gonzo, please take my word for it that with the proper bias from an external source, any combination of metals is protected against galvanic corrosion.

The actual process of electrolysis, involving Zn+ or Al+ ions being released and reacting with negative ions in the electrolyte while electrons travel through the metal junctions is too complex for this thread and confusing for most readers, so I took some shortcuts in my last answers.

Re: the outboard shaft.
When running there is an oil film insulating bearings, gears and ultimately between the stainless shaft and alloy housing.
When not in use (most of the time), the oil film is broken and there may or may not be an electrical path between shaft and housing. Such a path also exists between the shaft and an aluminum prop.

Because the bare surface of the shaft is very small, there is only minimal corrosion of the alloy parts.

 

Oh My the boys are at it again, the KISS principle, the metals on the lower end of the galvanic scale are not robbed of it's structure because there is an overriding source supplied by the outside active device. The caretaker is not eaten because an ample supply of raw meat is readly available.
CDK confirmation on my take, all the different nobality levels of metals present will feed off the supply to different amounts in that it satisfys their differences of potentials thus prevents them from feeding off each other. Is my general drift ok here. Geo.