Tim, not all spreaders fold. Mine don't. In which case it may be easier to simply raise the mainsail and use binoculars or a camera with high zoom to check that the main really goes up all the way (it's hard to verify that from inside the boat), but I've used shore-side photos to double check. Alternative is to lay the mast on some saw horses, that would leave the main a bit less supported, but we are only looking at the luff.
Seasick, my main halyard has a thimble spliced in it, to be used with a shackle to connect to the head board. That setup worked fine with my old sail, but I began to have some doubts whether it was too much distance for my "new" sail after it had seen a few seasons. I would normally have simply forgot the shackle and replaced it by a knot, but the thimble didn't want to pass through the grommet.
So, I decide to use a luggage tag hitch (modern nickname for "cow hitch").
Normally you tie this by pushing a bight through the grommet (or the hole in the luggage tag, or the cow's nose ring), and then threading the two free ends of the rope through the bight. Alternatively, you can pull more of the bight through the hole and wrap it around the luggage tag. This works well if you don't have a free end. Neither method works well with a halyard attached to the mast (only one free end) and a sail (to big to "wrap").
OK, now comes method third, which works if the grommet isn't too small compared to the diameter of the halyard:
- Push a generous bight through the grommet
- Push the single free end (with its thimble) through the bight, (leaving lots of slack and a generous tail).
- Pull the bight back out
- This pulls through the free end, which now forms a bight on the other side of the grommet and around the standing part of the halyard
- Loop the tail of the free end through the bight as well, to complete the hitch
Having a thimble, or a bulky stopper knot at then end of the halyard prevents the free end from sliding back through the hitch and undoing it (for example, when the sail is flogging). I've used this hitch for a season or so and it's never failed and given me a good three inches of extra room to raise the sail.