I was too cheap to go with an all spectra main halyard with a half-cover, so I used 1/8th" Amsteel for the half that will be under load and spliced that onto a 3/16" double braided (Samson XLS) using the excellent instructions on
http://l-36.com. The XLS is loaded only while raising the sail and its stretch characteristics are therefore not important.
Allen calls the splice a
Halyard splice, and I found it a fun project. Amsteel is 12-strand single braid and that makes for really easy splicing - in fact doing something like an eyesplice in that material is far simpler than in double-braid, and even simpler than in traditional 3-strand rope.
While at it, I also eliminated the shackle between halyard and headboard, because it caused my sail not to be raised to full height. That means not actually doing an eye splice and thimble at the end. Instead, there are several options for the end of the halyard.
One is to put a toggle at the end of the halyard, perhaps using a plastic ball and/or a bulky knot, like a
diamond knot. Here are
instructions how to use this setup with a toggle. With a knot or a ball, I change the last step shown in
so that I lead the knot/ball back through the loop, making a cow hitch. That has worked well on my main and saved me the trouble of having to fashion a toggle or splice anything.
The others are to splice some form of soft shackle into the end of the halyard, such as this
Hybrid Soft Halyard Shackle. I've done a similar version of this and all I can say is that it's rather easier than it looks. If you dig a bit deeper in the
L-36.com site, you will find instructions for alternate designs.