Very few
rope clutches will hold the main or
jib halyard without some slippage. The clutch clamps onto the jacket, which has some give, and allows the
core, which takes the load, to slip somewhat.
Ways to handle this:
1. Leave the halyards on the associated
winch after hoisting (what most racers do). If not using a
self tailing winch a cleat is required to hold tension on the line.
2. Add a second clutch in series with the existing one.
3. Use a "winch release" clutch which has a firmer grip than the typical "manual release" version.
4. Use a 2:1 halyard to reduce the load at the clutch. To make this
work the loaded length of the line needs to be the same diameter as the original halyard.
5. Stitch "load breaking" points through the jacket and
core every 5 meters or so along the halyard. I have done this with an older halyard on which I did an end-for-end update, which required shifting the jacket along the core. It seems to
work.
6. Aside from sending a crew aloft to tie off the halyard and installing a masthead halyard lock, neither of which anyone is doing, that's all I have.