Is an open or twisted leech a good thing or a bad thing?

I had always assumed it wasn't good but can it used for depowering? When we've been overpowered I usually put on lots of kicker and cunningham but that would straighten the leech when perhaps we're supposed to be letting the wind spill out?

Laser Vago in this case.

So if the mast is stiff then would twist be better suited it we're never going to get the sail particularly flat?

Maybe, but only as a last resort.  Its still probably better to get the sail as flat as possible and let the main out. 

And, of course, Jim's right. Rigs with full length battens and large roaches work differently. 

Thanks all.

At Rutland at the weekend (very windy), while beating the wind was hitting the back of the sail so hard that it was popping the battens the wrong way.

Presumbaly in this case the sail was no where near flat enough?

It probably wasnt flat enough. but i know in some classes if you over tighten the kicker the batterns will invert. so perhaps it needed to be eased a few inches.

also when dropping the mainsheet the jib should be going down as well to stop the front of the main backing. it keeps the slot open as well. Its far faster in those conditions in all venues (well all the ones ive visited) to keep the bow down ease jib and main together and power on through the gusts and watch the guys that pinch and rag their sails go backwards. only problen is that it is seriously physically demanding.

btw this is just something that ive found in the RS classes, it does vary as Jim has said between boats, and sailors

I like the idea of the crew working the jib sheet. Why should I have to do all the hard work

I'll give that a go too.

We've always sailed with the jib hard on when going up wind pretty much regardless of wind strength.

It sounds like it's more sensible to let it off a little to depower and reduce the main backing when it too is let off a little?

All these new things to try. I'll have to right myself a list to take out with us.

On some classes (RS400 for example) the boat is EXTREMELY sensitive to jib sheet tension.  Always let the jib out if you let the main out. 

BTW GRF, the jib slows down the air flow over the main, not speed it up.

Could you break that down a little? Our shrouds and lowers are still on factory settings. The lowers are if anything quite loose. What effect does the lowers tension have on sail shape?  I was as interested as you with the explanations of the adjustments made on some of the boats in the Endeavor Trophy. Somebody mentioned they moved the spreaders foreward and out. I can't work out in my head what that would do.

It's all interesting stuff. Keep it coming!

Sail twist (wind 25-30knts)

So was that by accident or intentional?

intentional. (i hope)

It was very windy and some big waves, so the rig tension was let off making the jib slot open up.   we had max kicker and loads of cunningham opening up the top of the main sail but notice the main was still brought to the middle.  Made us go very fast that day

I think this is where it gets confusing. I would've expected max kicker to tension the leech and therefore stop the sail twisting.

I suppose the cunningham would flatten the sail at the top allowing it to twist.

Apologies for taking this of topic, but yes, I'm absolutely certain.  Take a look at these for a thorough explanation of the process:

http://www.arvelgentry.com/magaz/Another_Look_at_Slot_Effect.pdf - http://www.arvelgentry.com/magaz/Another_Look_at_Slot_Effect .pdf

http://www.arvelgentry.com/techs/A%20Review%20of%20Modern%20Sail%20Theory.pdf - http://www.arvelgentry.com/techs/A%20Review%20of%20Modern%20 Sail%20Theory.pdf

I might come back to them in a year or two's time

I'll try and keep it simple.  Ignoring drifting conditions you sail in 2 basic wind conditions - you are either under-powered or over-powered. 

Under-powered requires a rig set-up that produces maximum force and if it produces a lot of heeling force that is of little consequence because you can always hike a bit harder.  You therefore want full sails sheeted as close to the centre line as they will go.  Too close and they will stall especially at the top so some twist is good and you control that with mainsheet tension.  No kicker or downhaul will be required with a conventional rig.

Over-powered requires a rig that minimises heeling force (you still want as much forward force as possible).  Flat sails produce less power and less drag so apply kicker to bend the mast but this hooks the leach so apply downhaul which opens the leach.  Open the slot too by moving the jib fairleads out or back.

You could of course lose power by setting the sail up badly by not appling any kicker or downhaul but you then have a sail which flogs.  A flogging sail produces a lot of drag and is "snatchy" (either on or off) which is very difficult to control.

So in strong winds you want flat sails and if you apply a lot of kicker and downhaul you'll see the top batten go almost straight meaning that the top of the sail is producing hardly any power (and hence hardly any heeling force).  And because the sail moves in and out like a barn door it is easy to modulate hence you can easily increase and decrease the heeling forces that fluctuate so much in the turbulent air of strong winds.  Incidentally a bit of twist in inevitable in strong conditions.

Sheeted as close to the centre line as possible?  Are you sure?  Won't that hook the lower part of the sail?  Surely that can't be fast.

I've always thought I should use the kicker to bring the leech close to parallel with the boat centre line and leave the boom away from centre to maintain that shape a the bottom of the sail  - and if it's really windy, let off the lowers so that the kicker also bends the mast and flattens the sail.

Anyway - with the Vago specifically, the mast despite being straight section, is really quite bendy; it manages gust response by having a fat headed main which causes the top of the mast to bend off more than the rest of it in gusts - ie the mast bend characteristic is determined by the sail shape rather than by the mast section, so you can use lots of kicker in confidence. 

Quite the contrary was my old laser 2 "fun" that had a very stiff straight section mast (more like a scaffold pole). All applying kicker did was pull the leech in without flattneing the sail, which made the sail more powerful not less. Not good.

So on a Vago in lots of wind, let off the lowers, apply lots of kicker and as Redback says, apply some cunningham too to open the leech a bit more. You could also reduce the batten tension a bit before putting the sail up. 

The jib should be in tight and you can head up wind to de-power, a loose jib will flog and pull you sideways without driving you forwards.

... and AlexM :  I'm intrigued by your letting rig tension off in a strong wind.  How does that work?    I've been piling ON rig tension in a blow to stop the jib hogging and induce some mast pre-bend.  Then making the slot wider by raking the mast back, which also has the advantage of twisting off the jib leech to dump a bit more power. (irrelevant on a vago as it can't handle rig tension anyway!)

Well you can't quite get the sail on the centre line.  On a 4000 we use a strop to get the boom as near as we can - which proably puts the lower leach more or less parallel to the boat axis.  You have to remember that a fast boat like a 4000 can be beating at 8 or 9 Knots in a 10 Knot breeze so that'll mean the apparent wind is only about 25 degrees off the bow - so the sheeting has to be narrow compared to say a Laser which is not going to get above 5 Knots.

It very important not to hook the leach at the top which is why the kicker isn't used and its controlled by the mainsheet tension which can be continually hardened or eased acording to pressure.  If the top does hook the sail stalls and the rudder suddenly goes dead.

I might just mention something which at first seems counter intuative.  On faster boats the increased speed which come from increased pressure is worth taking advantage of.  So unlike slower boats which luff when over powered and thus gain hieght.  The faster boats drive off in the gusts and just go faster.  We actually have to ease the jib a bit.

But I was trying to keep it simple.

Understood. 

Unfortunately it just ISN'T simple is it?

The next time "moderate" conditions occur I shall go out and try beating up and down the lake with no kicker on. It will be good for my arm strength if nothing else!

OK a bit more detail about the kicker.  I'm talking about under powered conditions.  The kicker goes slack when you apply maximum mainsheet tension but there has to be something to stop the sail twisting right off when you bear away at the windward mark.  So you need enough kicker to stop excessive twist on the reach but not so much that you're going to bend the mast and/or hook the leach when beating.  So my judgement is you should see all the weight go off it when you sheet in and then you can play the leach tension when you're going upwind.  The idea is to keep the boat powered up to the maximum that you can so keep bringing the leach up tighter until you see the top tell tale stall then ease and start the cycle all over again.  That way you're keeping the sail at its most powerful. 

As soon as you are over powered its a different ball game, then you start using the kicker to de-power the rig and keep the boat from heeling and incidentally save your arms from having to take all the leach tension through the mainsheet.  Without kicker in those conditions the mainsheet will be unbearably heavy in a boat like a 4000 and the sail will rag causing a lot of drag.