I can suggest you investigate the following:
Are you getting friction from the reefing lines (slab reefing) if you have any? If you have two or more dets of reefing line make sure that they are not pulling or even running through the grommets as you raise the sail. Thhis can impart a LOT of resistance at the end of the hoist since the reef line are at the bottom of the sail and they would have no effect at first.
Is the vang loose and is the topping
lift lift the boom so IT carries the weight of the boom and not the sail?
Are you
head to
wind so that the sail is luffing as it is hoisted? If not you may be putting latteral or rotational forces on the slides.
Are the slides free to rotate? This is both important and can be a problem if they bind?
Do you have a dutchmen system which is not properly installed? This too imparts lots of friction increasing as you raise the sail.
Try this:
Without the sail, tie a down all to the
halyard and make sure that the friction is not in the halyard "system". it should have no resistance all the way up.
Next, aemove ALL control lines from the main. Leave the halyard of course. Set the topping
lift to hoist the end of the boom pretty high. Slack the vang and the main sheet. Give it a try and see if this solves the problem. If it does, your friction is from the control lines.
Now with the same set up, liberally spray all the slides with Boeshield or silicone and see if this IMPROVES the ease of hoist. If it does, you have a problem with friction of the slides on the track. If it doesn't you have a problem of the wrong slides, or not properly installed ones or perhaps a defect at the top of the track too.