[RichH]

Use non-stretch modern polymer line such as 'dyneema', or 'am-steel' etc. Typical daron polyester is simply too 'stretchy' to be used for halyards, especially if you heavily load-up your halyards to affect good sail shape and to hold that shape during 'heavy' wind conditions to prevent the sail(s) from 'power-ups'.

The only problem in replacing with polymer is if your current wire-rope halyard has a 'ball' swaged to the wire and the 'ball' fits into into a special 'ball cleat' to hold the wire tension (instead of a horned cleat).

 

[RichH]

I was wondering if you pulled this off in the Columbia 26? I am about to change mine and i don't like surprises. I have a 69 columbia 26mkII i just bought for $600 and it needs new running rigging and I want to ditch the wire. i bought some amsteal 5/16 and spliced that onto 3/8 newengland sta-set. i am worried about the sheaves being too small

What you should be concerned about is that the 'good' wire-rope halyard systems used a sheave with a double groove in the face of the the sheave 'wheel' - one groove for the larger rope section and an additional smaller groove in the middle of the 'rope face' for the wire .... the transition between the two can be quite sharp. Such didnt matter on a rope-wire halyard as the rope section didnt bear any strain as it was simply a messenger for the wire section; the rope didnt bear any strain. Such wire-rope systems had the (ball) cleat near the top of the mast and the wire had a series of 'balls' swaged to the wire that engaged the ball, etc. cleat. Still a damn good system where used correctly - IMO.