Joe, just as all sail controls are integrated ...
in the way we adjust them, all discussions are related as well. I don't look at it as re-opening an old argument. It's more like a related discussion.
Here is the reference to RichH's discussion:
"The chief ‘control’ of twist is ‘how hard’ one pulls **DOWN** with the MAINSHEET. This puts strain along the leech and ‘twist’ is reduced, the overall sail camber increases with increasing MAINSHEET strain and the resultant is that the sail ‘powers-up’; conversely, easing the mainsheet tension ‘opens’ the leech, allows more twist aloft, can allow flow separation (flow no longer attached) at the head panels which depowers the sail especially in higher windranges which causes less heel, etc. Looking at ‘overtwisting’ in another way: the top of a sail that is ‘overtwisted’ is akin to putting in drastic ‘overdraft’ or so much draft aloft that the flow separates at the area of ‘overdraft’ .... a separation stall under high speed wind flow because the shape is ‘too round’ and the draft ‘way too much’ !!!!
The LIMIT of how much the sail can be twisted is set by the VANG and the Traveler ..... because the traveler can set to be almost directly UNDER the sail which can ‘substitute’ for the amount of mainSHEET tension. Using the traveler is faster and vastly more precise to control the amount of twist.
Setting up the CORRECT amount of twist is to get precise MAXIMUM speed/power out of a sail, is NOT a long term substitute for reefing nor flattening nor for ‘blading-out’ a sail to correct/trim for too much ‘heeling’ moment, etc.
In ‘blading-out’, an adjustment done with solely the traveler – sometimes called “‘playing’ the traveler”, the already set angle of attack ‘all the way up’ through the panels stay essentially the same or unchanged, and the sail begins to ‘stall’ under a uniform manner and at a consistent (and usually predictable) manner along the WHOLE sail.
In contrast, by allowing the boom to rise, when ‘dumping the mainsheet’ to allow more twist at the top, the leech does ‘open’ but also at the same time the lower and MIDDLE panels of the sail become MORE DEEPLY drafted (powered-up). Yes, the top panels are now ‘essentially flogging’ (reducing the heeling moment); but, the center panels are now set up to be in SECOND GEAR deeper draft and thus ‘progressively vulnerable’ to drive the boat further over onto her beam ends, if the helmsman isnt that quick or experienced ..... all set up for a ‘dumping’ if the wind is more powerful than the boat/helmsman can handle ... OR if there is a significant windshift .... because the twist (overdraft) is now down into the middle and lower portions of the panels and they are now at MORE draft than when the 'twist' was set correctly.
“Blading-out” with the traveler doesnt allow the draft to change to a more ‘powered up’ shape, the sail stays flat and is restrained from changing to a ‘powered-up’ shape .... because the boom can’t rise (even ‘rigid vangs’ will have some amount of ‘stretch’). "
My take-away here is that both sides of this discussion are essentially correct. Mainsheet tension tightens the leach and increases camber at the head of the sail. Easing the mainsheet opens the leach and flattens the head of the sail (induces twist) but deepens the draft at the lower sections of the main sail (power-up).
and :cry: (lots and almost none). Playing with the backstay today - in almost :cry: wind - the backstay did seem to open up the top of the leech. The backstay definitely reduces headstay sag on my boat.