I had to send my Glaser main sail (circa 2008) in for some work and took out the battens. I don't recall them having much bend when I took them out. Any rule of thumb here for general conditions?

The harder you push them into the sail ie. tighter string tension, the more -curve- (or Draft) you are pushing into the mainsail. If you want a flatter sail for very light or very strong winds, you don't want the battens too tight, just enough to pull the wrinkles out of the pocket. If you want more draft for medium wind, then you want them in tighter to push the draft into the sail, but sometimes when they are tight, if the wind drops, you may have to "snap" them over when you tack, by pulling back quickly on the boom, as they won't come over with just the light air pushing them.

It's a tough call from the internet, without knowing the wind and the stiffness of your battens.

Note that Timbo's right, but the effect on modern sails are far less than on Dacron sails of old. There is a really limited range you can play with, the draft of the sail is mostly set by the sail maker: you can't really stretch modern sail that much to build a draft.

What I do is to put the batten in so there is no wrinkles and forget about them.

How much of the shape is related to diamond wire tension?

Tension and rake => pre-bend => influences shape a lot

The very top batten is always difficult to adjust properly and there is one batten in the center that seems to want to bend in toward the windward side of the sail.

Pre-bend affects the midsection of the sail the most. Top batten not much really.
Sounds like your mast and sail dont match up very well if the mid batten tries to take an S-shape. How old is the sail? If the sail is OK and the batten is not tensioned hard I would have tried to increase pre-bend a bit. But first check that the batten protector at the luff is mounted the same distance from the luff rope as the rest of the protectors.

What is the problem with the top batten? It is quite common to switch the top two battens between soft and stiff for weak and strong winds respectively.

Sails change with time..

Hard to quantify. Tight, but not desperately tight.

First step is to tie the battens in correctly. When you thread the tension lines you end up with one end of the line in each hand and you push the batten in with your thumbs. If threaded correctly you can let go of both the lines and the batten without loosing the tension. I tried looking for some pictures on how to thread the lines and do this but I did not find any.
Once you have the battens tied in correctly, it is easy to set the tension you think is correct, hoist the sail and have a look with some sheet and downhaul on. I usually just put them in firmly and that does the trick for all conditions.

This is how I do mine.

These sails are less than a year old. I think it's just tension, but I'll ask some of the experts Sunday or Monday.

After having some alterations carried out on my Landy Main I asked Grant Piggott for his advice on batten tension. He reckoned you need just enough tension to make the battens pop from one side to the other. Thus not a lot of tension is required. However, I have now got into the habit of loosening the top three battens after every race and then re-adjust the tension prior to every race for the predicted conditions. Tight for light and loose for lots of wind. I can't say I really notice any difference but psychologically it feels much, much better so must be faster

In light winds you really don't want the battens too tight because they wont pop after a tack or gybe (very annoying!).

With heavy winds its more effective to switch to harder battens than to change tension.

If they dont pop over in light winds, give a pull on the downhaul and pull the boom over, then trim the downhaul to your prefered setting again.

Tony, how do know how my battens react? Contrary to what you think in light winds they are not annoying at all and 99% of the time pop over whilst tacking even with quite a bit of induced tension. I agree about stiffer battens for stronger winds but I'm quite happy just to tie my top three battens so they don't fall out of the luff batten pockets. It's cheaper

I heir-by apologize to your battens, I did not mean to upset them...

Do I sense som "tension" here

Soft battens in strong winds can get a really nice S-shape. It is probably not noticeably slower but it sure dont raise the mood onboard.

Am i the only one completely releasing the tension from ALL the battens every week? I don't think I could sleep right with them under tension all week....

barbarians!

I sent Jay Glaser and e-mail and this was his response:

The battens should be just tight enough so that there are not any vertical wrinkles coming out of the batten pockets when sailing.

It turns out this is fairly tight.

Too tight and the sail will look like a hungry dog with more shape at each batten and less between.

When inserting the battens make sure the forward end is as low as it can go in the pocket so it is pushing on the lower forward bolt in the plastic protector.

Sail fast,
Jay Glaser

I'll be looking at people's sails this week at GC. I came here with a list of questions and so far I have gone through a couple of them and people are very willing to help.

So what where the other questions you had and the responses you got?

As this is my first season, they are pretty basic, but make a big difference in the wind we'll have this week. One was simply where do you put the stick when taking down the spin? (I sail single handed). The first answer I got was tuck it between your bent legs as you kneel to pull down the spin. It keeps it steady and well within reach should things go bad.

The second was even more basic, but had to do with keeping your mast from flapping side to side in high winds on the beach. Two answers - center the mast rotation and cleat or pull the mast rotation to the side & tie off so that more of a profile is facing the wind.