When going downwind, the true wind is about 45 deg behind the beam, since you are sailing about 45 deg above straight-downwind. But the apparant wind, due to your boat speed, is forward of that - - aproximately abeam. I say aproximately because of the different true windspeeds near the surface and 20 feet up. The faster winds aloft "counteract" your boatspeed somewhat, and so the apparant wind is further aft on the top of the sail.
Rick's advice, which has worked splendidly for me, is to have telltales attached a foor forward of the leach, one set a few feet up from the foot, one set just above the hounds (that's where the forestay attaches). Set the lower tells with your travelor, set the upper ones with your sheet. You'll notice your leach is much more open on top (in response to that above mentioned difference in apparant wind) This means your sail is twisted, hence "twisting off"
Downwind, most sailors agree this is desirable, with no downside, as the extra fullness caused by the loose mainsheet is a good thing, usually, anyway, the fullness is less counterproductive than it is upwind. Upwind, Rick's opinion, shared by many hot skippers but not all, is that you want to sheet hard to flatten, traveling out as needed to de-power. The depowering order of operations upwind is: Trap, downhaul/outhaul, travel. Pinch up only to survive. Loosen the sheet on a monster puff, if you absolutely have to.
Some sailors believe that a tight traveler and loose main will open the top leach, lowering the center of effort of the sail, reducing heeling moment. I've heard people praise Nordic H16 sailors for this technique. My experience is limited, except to say that I've had better luck with Rick's method. If you Downhaul the living spit out of your mainsail, the top leach wants to open even with a tight mainsheet. So you can sheet hard, still open the top leach, but have a much flatter sail, which in turn slips through the high wind easier, letting you go faster.
Still, we went out in a H16 raked all the way back, in extreme conditions last week, and the talented novice skipper twisted off most effectively - in that I'm still here to talk about it! He tried traveling out and sheeting hard, said it hurt his pointing, so he went back to what was working for him.
Different boats may yield different results. Actual California Highway mileage will probably be lower.
