(numbers in inches of my downhaul measurement sticker)

I think my mainsail luff starts off untensioned at 2 or something. I then pretension it to 4 or 5. I do this as Paul says. Pull the blocks in the mast all the way up, then cleat the handheld downhaul line and then pull the sail down to number 4 or 5 before tying of the downhaul line itself.

While sailing I quickly need to go to 6 or 7 when putting on some moderate mainsheet tension.

With strong winds I have gone as far as all the way down to the boom = 10, with a mainsheet cranked on hard.

This would indeed be something like 8 inches of downhaul travell and the mast does show a major curve then.

It is easy to get down this that setting on my boat when pulling on the mainsheet and downhaul at the same time or first pull on the mainsheet and then pull on the downhaul after which some more mainsheet is pulled and again some more downhaul.

The only thing to be cautious about is slacking the mainsheet totally when the downhaul is still set to 10. This puts ALOT !!! of downhaul tension on the luff of the mainsail and it does not really like that happening too often. So let of some downhaul before slacking the mainsheet by large amounts; like after the finishing. 3 to 4 inches slacking is enough then.

Wouter