I have been reading some postings regarding twist that I haven't agreed with (and the posters are a couple of folks who know a lot more about sail trim than I do, I am thinking) so I feel like I need to hear some thoughts to set the issue straight.
Alan says that sail shape is flattened in gusting conditions to limit power. He and RichH both agree that moving the traveler down or 'playing' the traveler is the correct thing to do when reacting to gusts so that the main doesn't twist off and 'over-power' the main. They contend that easing the mainsheet allows the main to twist off and over-power the vessel at the height of a gust.
I understand the concept that easing the mainsheet 'loosens the leach' and allows twist. Where I diverge is the idea that a twisted-off main is overpowering. First of all, I don't consider that the adjustment of twist is a 'flattening' technique or as a 'power' adjustment. I consider that sail flattening is a function of outhaul for draft shape, and halyard tension and cunningham for draft position (and you could add back-stay tensioning - but doesn't that also loosen the leach?). Yes, the outhaul is for draft shape at the bottom of the sail, and I get it that when talking about the head of the sail sailors will refer to twist, but I consider that twist is either set correctly or it's not. If twist is correctly established, the airflow will not over-power the sail at the head. In other words, you would not purposely reduce twist for gusty conditions, particularly because a sail that is stalled at the top feels over-powered and causes the boat to heel excessively (which leads the sailor to want to change the angle of attack and basically block the boat from the best speed). Basically, I also consider the primary 'power' adjustments to be the outhaul, halyard and cunningham to establish draft shape and position.
I consider that twist is essentially a speed control. For optimum speed, twist is set correctly ... under-twisted is slow, sluggish and creates the illusion that the boat is overpowered because the head of the sail is stalled. Over twisted has nothing to do with power, but it is slower because the sail is inefficient at the head.
If anything, isn't a twisted-off main under-powered?
So this takes me to my experiences ... basically, in gusty conditions, on a close haul, I want twist. I find that if I center the traveler, and sheet in tight, I essentially have stalled the mainsail at the head because I have reduced twist. Since my traveler is too difficult to adjust (it is on track right where people sit and the track has stoppers, not line controls), I ease the mainsheet. Sure it increases twist, but it also changes the angle of attack and really slows the boat. But the worst part is that because the main has no twist to begin with, I get that over-powered, rounding-up problem all too frequently.
I have been experimenting and I find that when I move the traveler to windward, maybe up to half way to the end of the track (from mid-point), I can ease the mainsheet to center the boom AND induce twist. I sail faster, I sail higher, I find that gusts have much less impact (except that I usually get a lift that helps me sail higher) and my adjustments to overpowering gusts are far less severe and less frequent. Rather than over-powering the main when easing the mainsheet, I find that I make smaller adjustments to angle of attack which is the most significant boat slow-down maneuver I can think of.
In short, I find no downside to 'playing' the mainsheet in gusty conditions when I have the traveler set in the optimum position. What am I missing? I am wondering if boat size is an aspect that impacts this discussion.
Also, I have (twice) seen RichH refer to the traveler in regard to twist adjustment. Since we all know that the traveler only impacts angle of attack, I must be missing part of the explanation ... is it with regard to establishing twist as I described above?
Alan says that sail shape is flattened in gusting conditions to limit power. He and RichH both agree that moving the traveler down or 'playing' the traveler is the correct thing to do when reacting to gusts so that the main doesn't twist off and 'over-power' the main. They contend that easing the mainsheet allows the main to twist off and over-power the vessel at the height of a gust.
I understand the concept that easing the mainsheet 'loosens the leach' and allows twist. Where I diverge is the idea that a twisted-off main is overpowering. First of all, I don't consider that the adjustment of twist is a 'flattening' technique or as a 'power' adjustment. I consider that sail flattening is a function of outhaul for draft shape, and halyard tension and cunningham for draft position (and you could add back-stay tensioning - but doesn't that also loosen the leach?). Yes, the outhaul is for draft shape at the bottom of the sail, and I get it that when talking about the head of the sail sailors will refer to twist, but I consider that twist is either set correctly or it's not. If twist is correctly established, the airflow will not over-power the sail at the head. In other words, you would not purposely reduce twist for gusty conditions, particularly because a sail that is stalled at the top feels over-powered and causes the boat to heel excessively (which leads the sailor to want to change the angle of attack and basically block the boat from the best speed). Basically, I also consider the primary 'power' adjustments to be the outhaul, halyard and cunningham to establish draft shape and position.
I consider that twist is essentially a speed control. For optimum speed, twist is set correctly ... under-twisted is slow, sluggish and creates the illusion that the boat is overpowered because the head of the sail is stalled. Over twisted has nothing to do with power, but it is slower because the sail is inefficient at the head.
If anything, isn't a twisted-off main under-powered?
So this takes me to my experiences ... basically, in gusty conditions, on a close haul, I want twist. I find that if I center the traveler, and sheet in tight, I essentially have stalled the mainsail at the head because I have reduced twist. Since my traveler is too difficult to adjust (it is on track right where people sit and the track has stoppers, not line controls), I ease the mainsheet. Sure it increases twist, but it also changes the angle of attack and really slows the boat. But the worst part is that because the main has no twist to begin with, I get that over-powered, rounding-up problem all too frequently.
I have been experimenting and I find that when I move the traveler to windward, maybe up to half way to the end of the track (from mid-point), I can ease the mainsheet to center the boom AND induce twist. I sail faster, I sail higher, I find that gusts have much less impact (except that I usually get a lift that helps me sail higher) and my adjustments to overpowering gusts are far less severe and less frequent. Rather than over-powering the main when easing the mainsheet, I find that I make smaller adjustments to angle of attack which is the most significant boat slow-down maneuver I can think of.
In short, I find no downside to 'playing' the mainsheet in gusty conditions when I have the traveler set in the optimum position. What am I missing? I am wondering if boat size is an aspect that impacts this discussion.
Also, I have (twice) seen RichH refer to the traveler in regard to twist adjustment. Since we all know that the traveler only impacts angle of attack, I must be missing part of the explanation ... is it with regard to establishing twist as I described above?