Jib downhaul:

I have to admit that I've never sailed a cat with an adjustable jib downhaul and it seems that all the go fast boats have them so I have to assume that understanding how to use it helps you go fast...

Being very naive, I would assume that honking on the jib DH flattens the jib just as honking on the main's DH flattens the main, but I suspect it's not all that simple. With the main's DH, you end up bending the mast which is what really flattens the sail. So I'm not sure I see how a jib DH would flatten the jib. Maybe by tightening the luff of the jib it's giving it less "sag" and therefore less shape... That raises the question of whether changing jib DH tension also changes the effective forestay tension, the overall rig tension, and the effects that those may have...

Then there's the whole issue of moving the draft. As I recall, on the main, adding DH moves the draft forward, which I think I've read effectively makes the foil less powerful. If it does that, I'm now sure I understand why (I should have paid more attention at the time). I would assume the same thing happens for the jib?

Anyway, as you can see, a little bit of knowlege (and a larger lack of knowlege) is just plain dangerous. So this would be a great time for a short jib DH primer to set me straight. So what's it for, why does it work, and when do you adjust it? How much of a difference does it make?

Self tacking jib traveller:

In a recent post I read someone mention that the jib "barber hauler" on a Blade's self tacking jib didn't help and actually hurt sail shape and power when it was used. I'm assuming they were referring to self tacking jib's traveller since I don't think Blades come with jib barber haulers. If I understood them correctly, they said if you just left it slack, the car found a decent sheeting angle automatically due to sheet tension and kept a better sail shape in the process.

So my question is have other people experienced the same thing? Is this issue related to a specific sail cut being slightly off, the self tracking track being bent or improperly shaped, is it boat specific, or maybe was the setup not optimized (ie, it would have worked better with more jib DH)?

So how do you guys adjust the jib traveller and jib sheet for upwind vs downwind? Do you actively ajust the jib traveller or just leave that line slack? Do you adjust the traveller and/or jib sheet differently for upwind vs downwind or pretty much set it and forget it? Do you do that differently for singlehanding vs doublehanding? Spi vs no Spi? Lighter vs heavier wind?

As a well respected sailor once said: "The questions remain the same; only the answers change"...

Jerry

My personal experience on my Nacra 6.0na, is that the jib downhaul does work. It makes a noticible difference on that boat anyway. On other boats it might not make as big a difference. I also compared an old jib to a new, flatter jib, and much preferred the old jib in light/med air.

I would be curious to know if anyone else is doing anything with this control, and how they trim it.

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..