OK, so I've priced the spectra from Whitworths, and may opt for 12mm at this stage, not so much for the strength, but so I don't have any problems with the deck jammer not retaining the halyard. Might get a sample of 8mm and check out whether it slips.
The next question is connection to the top plate of the sail. Some have said, splice a stainless eye with a captive shackle. Others on other forums say use a simple bowline with no shackle. Then there is the idea of just tying a big stopper knot as in
http://www.sail-world.com/Cruising/Five ... sing/59962 (look at point 3).
In speaking to the manager at Mona Vale Whitworths, he suggested tying a bowline around a stainless eye, then whipping the tail of the bowline so it's neat, then using the usual captive shackle, hence not needing to splice, or worry about a bowline slipping undone and having the halyard run through the sheave..... in his opinion a knot in spectra isn't going to weaken the cord by enough to make it a worry.
Thoughts, just to try and rid the clanking halyards at anchor.....
Michael