So many questions, and so little intelligent to reply with..

Jib downhaul: Yes, it works and indeed moves draft forward but also flattens your jib. A draft forward jib is more forgiving than one with draft further aft, so you definately use your jib-downhaul to shape the jib for the conditions. A jib with draft further aft have a theoretically higher top-speed, but it depends on how good the skipper is and how you set it. The jib downhaul flattens the jib by tensioning the cloth, so depending on how the fibres in your sail is laid up it works proportionally well. The same thing happens with your mainsail, first the cloth is pulled tight and moved a little bit, then the mast bends and the already tight cloth follows the mast.
Depending on how the forestay is set up and how the jib is buildt, it "can" do something with forestay sag as well, but mainsheet tension is far, far, more important in keeping the forestay taut. In really, really light winds where you forgot to tighten your shrouds, you can take up the 'slack' with the jib downhaul. Tightening the shrouds would always be better.

There was a long discussion last year(?) about wether the track for the jib should be straight, curved with a radius smaller than the foot of the jib or matching the foot of the jib. I think we split in two camps where a small group preferred a flat track where jib-tension pulled the car inwards and a larger group preferred a radius on the track matching the foot of the sail. Personally I prefer to have precise control on how far out the car sets, instead of trusting some other dynamic system for this. We set the car according to the conditions (30cm, 40cm and 50cm from center on our T) and only adjust it when conditions change. Sheeting point on the jib has a larger influence on shape than how far out the car goes and wether this tightens/releases jibsheet.

Downwind we release the car if we have time for it(many dont bother to do this, including olympic teams), and let out on the jibsheet until the midsections telltales flies. From there on, we let it be (assuming we fly the kite of course).


Dave: For really light winds (0-1m/s) a flat jib is faster than a deep jib. Problem with deep sails in this windrange is that drag is larger than the added power. The wind also have trouble following the surface of deep foils when it's not up to speed. In 2-4m/s, a deep jib will give lots of power, but an old jib often has draft too far aft leading to poor power and pointing. This is all relative of course, and lift/drag ratios move around all the time according to how you trim your sails and how windspeed changes.



Just my opinion..