[WhatTheFoley]

I changed out both main and jib halyards on my CAL 31' last season. I used uncovered Amsteel where the wire used to be and it went over my sheaves just fine. That said, synthetic lines (uncovered especially) DO NOT like UV. Use a sacrificial line (see below) if your boat sits at the dock for long periods of time. I made sure to add a cover (taken from another line) for the exposed part of the halyard that runs to the cockpit. Amsteel was much cheaper and has the added benefit of not getting hung up (wrapped) on the forstay when we are hoisting in some chop.

When I'm not sailing the boat within a day or two I rig up a line that I don't mind getting torn up that goes from the bow and connects to both halyards, then I run them up so that the uncovered sections of the rope are inside the mast. This limits the exposure that the lines have to UV. what little is exposed at the base of the mast I tuck under the sail cover.

 

[WhatTheFoley]

I went up to the top of the mast and checked out the sheaves. I was in the same situation as you so I wanted to be sure. I got my family to haul me up with a harness, and just checked to see if the sheave was big enough for the line I had in mind. Since I was using Amsteel the diameter did not need to be that big to match the steel cable I was replacing. The cover on the lower section added some diameter so that handling the rope wasn't a PITA.

 

[WhatTheFoley]

WOW...the whole family??? Just immediate family or extended family too? Just asking :laugher

It was just my father actually, my sister and mother were killed in a tragic sarcasm accident...