[Fstbttms]

so help me understand if electrolysis is an issue - how come the stainless shaft does not appear to have any electrolysis issue?

Because the shaft is likely not made of stainless steel, but rather Monel, just like the cotter pins.

 

[Fstbttms]

Shaft is big, and it is also towards the boat from the prop. So the electricity flow is from shaft to prop to water. This prevents much corrosion occuring at shaft. Pins are small and they are between prop and water, so since stainless is less noble than bronze, pins will act as sacrificial anodes and may dissolve relatively quickly.

This doesn't even make sense.

 

[Fstbttms]

why not?

1.- The size of the shaft relative to the pins and its position relative to the prop and boat do not affect whether or not, or to what extent, electrolytic corrosion will occur.

2.-

Pins are small and they are between prop and water...

so since stainless is less noble than bronze, pins will act as sacrificial anodes and may dissolve relatively quickly.

The first part of this sentence (besides being completely irrelevant) has absolutely no relation to the second part.

3.- The pins are made of monel because monel is galvanically closer to bronze than stainless is (as you correctly pointed out). However, this is to prevent galvanic corrosion, not electrolytic corrosion.