Adjustable Outhaul and Sail Twist

[konajoe]

If I increase my outhaul due to being overpowered, I'll make the sail flatter, but I'll also reduce the twist at the top. Won't that raise the ce of the sail?

If I reduce the outhaul in light wind, I increase the twist of the sail and dump the top. Am I really making things better?

[zirtaeb]

very little....
increasing outhaul does lessen the power you have to hold, but gusts still overpower you, so for me, it's better to increase the downhaul till it's maxed out, then start with medium outhaul and hope the winds don't die.
Deeper does get you planing, on a broad reach.
As the sail dumps wind, you can pump it, making the top drive you forwards.

[isobars]

Regardless of the details, it works for me. Overpowered or underpowered for a while, I may drop in the water and tighten or loosen my outhaul to good effect. Back when I bothered with adjustable outhauls, I'd sometimes be trying unsuccessfully to plane, until I pressed the outhaul "dump button" to allow an inch or two of slack and suddenly I'm planing. I'd guess the difference between max and min practical outhaul might feel like a quarter meter in small sail sizes ... something like 5% in sail size/power. Sure, we can feel the handling difference in very dynamic sailing, but I'll take the tradeoff if it saves me a rerig or if the wind is rising and falling more than I care to tolerate.

Mike \m/

[zirtaeb]

Since sail tuning requires fiddling with downhaul, outhaul, mast stiffness, and batten tension, if you don't adjust one of the above, you won't get the full benefit of tuning. And yes, tightening the outhaul does lessen the overall power, more than the tightened leech adds power in gusts.

[swchandler]

My take on things is that the top of the sail, which involves the twist-off characteristic of the leech, is predicated on the amount of downhaul, regardless of your outhaul adjustment. Within the margin of potential outhaul you've created, less outhaul will give you more power lower in the sail that you can use, particularly going off the wind. Tightening the outhaul will make any excess wind spill even easier, and it facilitates your upwind ability and speed to windward. However, some sails include two different clew positions of the outhaul. The higher position provides a tighter leech, whereas the lower one allows for a looser leech.

[konajoe]

First, let me say that I'm talking about on-the-fly adjustments, where outhaul is your only thing available.

I think a few of you have said what I was guessing. If you increase the outhaul, the effect of the flattened sail in the boom area overwhelms the negative effect of the tighter leach. And, conversely, the effect of a fuller sail in the boom area is more than the depowering effect of added twist.

It's kinda neat to watch it when you rig. Put your rigged sail on the ground with the mast 90 deg to the wind. Bring the back end of the boom up to eye level so that the grommet is in line with the mast. Tug on the outhaul and watch the twist change.

Already a few references to pumping. The tighter leach sail is better for pumping. Not the other way around. No doubt. Pumping with a loose leach is like rowing with a flexible paddle. Its easier to move the paddle through the water, but it doesn't propel you forward as well.

[LeeD]

Wrong again....
Modern sails pump you forwards.
The tight leech sails pump you sideways to the direction of travel.
Look UP at the sail while you pump, you will see the effect.

[swchandler]

Again, downhaul creates the concept of the loose leech. Outhaul doesn't change that. It simply it allows you to promote power lower in the sail by creating a bigger pocket, or reducing the pocket thereby easing release of air through twist along the leech.

The easiest way to understand the way things work is to look at upwind/downwind formula sailing. Nobody is changing their downhaul on the fly, except with something like an Olympic RSX kit. It's simply about playing with the outhaul. Downwind sailing is predicated on less the outhaul, whereas upwind sailing is grounded in tightening the outhaul. In the former position, less air is allowed to escape. Conversely, the latter position, more air is allowed to escape. Although it might seem otherwise, a tighter outhaul position makes the sail more slippery, and actually faster to windward.

[coachg]

[jingebritsen]

the kona/zenith sail has some very singular features.

very little luff curve. makes for very stark differences in twist with very slight amounts of down haul. every time i've gotten carried away with the down haul tuning, i regret it. 2-3 cm difference, max, unless you are trying to run thru gales, the down haul setting is not commonly going to help. i've learned to keep it aggressively under tensioned with all the kona class sails. they sail well set with minimal tensions into some pretty strong stuff.

out haul, if one has neutral or negative out haul tension, the sail will pump like a flaccid noodle. so, a statement that says "fuller is better for pumping," would be misleading. gotta have some tension for pumping. tends to break batten tips anyway on cam sails....

any RSX person can also add, any extremely under down hauled cam sail is prone to break batten tips. they went thru that for years, some may still do. they have an on the fly adjustable down haul, not worth doing for we mere mortals.