I'd noticed an interesting/disturbing phenomenon that last couple of times I used my boat; the once highly polished/shiny/smooth Rev 4 prop was dingy and very rough to the touch. Now perhaps coincidentally (or not), I have only noticed this since I installed my NOCO dual bank 10 amp shore power charging system.
The anodes on the outdrive seem fine, and I can only assume the Mercathode system is operating as intended. But Section 7 of the #28 Bravo sterndrive service manual indicates I might need a galvanic isolator; Quicksilver part number given.
Only the propeller seems to have any issues...the rest of the outdrive, the trim tabs, all look perfectly fine.

Thoughts?

I can’t say that it will fix your problem but you may be on to something.
I installed one when I installed shore power on my fountain.

On a side note, you may be able to test it or have an electrician test it. If I remember correctly, if you measure ANY resistance between the ground and outdrive/prop, you have an issue. Testing needs to be done with a good digital tester. It can go unnoticed with a cheap tester. I’m not an electrician, I only know this because our houseboat failed a state electrical inspection and It was from a bad isolator. Very small amount of resistance was measured between the ground and aluminum hull. This was years ago, seemed around 0.x ohms or 0.0x ohms.

Before throwing money at the problem guessing, get a marine electrician to look at it. You may save money and someone’s life.

I’ll also add, like you said, it may not be related. If the outdrive is not pitted, does not seem like it would effect the prop only.
I believe stray current damage would look like pitting.
If you keep it at a marina, could be from another boat?
Could the rough feel be from hard water build up?
Post a pic of your prop.

The boat is kept 300 miles away from my house, it's in dry storage on Table Rock lake in Missouri and I am in Wichita, Kansas...I meant to take a picture of the prop last time out but failed to...but will do so next trip.
When I am at the lake I stay at a private resort that I have been going to for 30+ years, and they have a private dock with about 20 slips. This is where I have the boat when I am on the water...usually anywhere from 3 to 7 day trips, several times a year. I had only recently installed the NOCO dual bank charger; in the past I had a single bank BATTERY TENDER model (6 amps) that charged both batteries, just very slowly of course, I had this same charger on my 208 Baja that I had for 30 years, and used the boat in exactly the same way as my 252...and never saw this phenomenon.
I did read that if ONLY the stainless steel prop is showing corrosion, it could be that it has lost continuity with the Mercathode system for various reasons...and they suggest a 'continuity washer' to be used or to thoroughly clean the shaft, prop mounting surfaces, etc to help alleviate the issue.
I know that people on this forum leave boats in the water sometimes permanently...my boat is showing this issue after having been 'in the water' for maybe 500 hours or so?

Thanks for the reply.

Don’t forget…it could also be a boat docked next to yours causing galvanic issues to yours.