I just now read this entire post for the first time.
Although a lot of attention seemed to be looking for a physical cause, there was not much mentioned at the time that "fraying of the main sheet"
was more likely related to how we trim our sails
. The general conclusion was that fraying: Seemed to located in the same area about, 4'-6' around the Harken Cam Cleat.
Was not the angle of how the line went through the cleat and would not be helped by installing a fairlead.
Was not caused by the screws on the chafe plate or anything related to the stern cheek block.
Was unaffected by the 3:1 or 2:1 ratio.
Might have something to do with "stress or load" on the line.
Interesting that this topic has renewed activity. However, other than replacement and or upgrading ones lines, not much seems to have been uncovered as to the route cause of the problem or how to reduce it from happening.
Here's what I think is going on:
A while ago I had a friends TI in my shop for some upgrades. We happen to notice that his main sheet was badly frayed (like the ones pictured in this post) and looked much worse than mine.... But I sailed more than he did. Same boat, same set up etc. So that made me curious...
Turns out my friend was in the habit of trimming his sail with the main sheet running directly through and in the Harken Cams while there was a load on the line
I generally lift or "pop" the line out of the cams, and then trim my sail. Although this is not always possible to do, (especially when there's a heavy strain on the line), my main sheet was not as frayed as his.
It seems to me that by comparison, our different ways of trimming our sails had a direct effect
on how much fraying our main sheets had.