Does the mast have a ClamCleat or a wrap-around cleat (see pictures below)? If it has a ClamCleat then you need a low stretch halyard with a sheath. Low stretch rope is really important as any stretch results in the mainsail pullingt down the mast when you pull the cunningham on. I use Marlow Excel Racing GP 78 4mm Halyard / Control Line, Dinghy Yacht Dyneema Rope. If you have a wrap around cleat then you can use 4mm dyneema without a sheath.

