S-Shape in Main going upwind. Why?

[gamayun]

How old is the main?

[Cavalier MK2]

Always good to read Dave Calvert's comments, sooner than later I'll need a new main and it's good to know what to look for.

One of the more interesting inexpensive round batten alternatives I read about are Reuel Parker's pvc plumbing pipe battens with epoxied wood inserts for stiffness. The stiffness can be varied by the type and shape of wood used. While not yachtie it can be a low cost way of trying different degrees of batten stiffness while evaluating a main.

[Don C L]

How did increasing the luff tension and batten tension work out? My main is nearly new and will get that S occasionally when I have not trimmed, tightened, tensioned it correctly, (I have a mono.) Or when it starts to luff 'course. Tell-tales might help. Couldn't tell if you had 'em. (Trying to help you avoid having to get a new sail!)

[Cheechako]

That looks real full in the luff also, the whole sail should be flatter, of course we don't know, maybe it was very light air?
The whole sail may be blown out of shape.
Initially I was thinking the battens are too compressed causing that S ?... Some of ya'll think they need to be tighter?
"No spreaders" on the mast? How straight does it look when you have that shape?

[StuM]

Originally Posted by gamayun

How old is the main?

I asked that about 6 days ago. Still no response from the OP.

[sailjumanji]

Originally Posted by gamayun

How old is the main?

Old enough that it needs to be replaced, because the cloth is shot.

[Snowpetrel]

Originally Posted by Cheechako

That looks real full in the luff also, the whole sail should be flatter, of course we don't know, maybe it was very light air?
The whole sail may be blown out of shape.
Initially I was thinking the battens are too compressed causing that S ?... Some of ya'll think they need to be tighter?
"No spreaders" on the mast? How straight does it look when you have that shape?

That why I thought easing the halyard tension might help. The high halyard tension drags the draft fwd and adds compression to the battens sometimes making the main deeper. More mast bend would also help flatten the sail. A good sail maker might be able to recut and reinforce the leech to reduce stretch. Prehaps by using an extra panel to make the leech area a two ply panel.

But this is going to cost a significant fraction of the cost of a new sail.

Definately worth playing with spreader tensions and stiffness.

[thinwater]

Look at the draft guys. It's a bag.

[chris in SG]

I've been following this closely because I've occasionally had exactly the same symptom, but not consistently. My main is only 3 years old and very lightly used, so as far I'm concerned, all the (rather dismissive) comments about age and 'blown' and 'shot' are unhelpful, though perhaps in some cases age is contributory.

From my own experience, it must be something to do with trim but I can't pin-point it yet. The suggestions here are helpful..

[Don C L]

Originally Posted by Snowpetrel

Definately worth playing with spreader tensions and stiffness.

Spreader or batten? Well I'll have to get out and mess with it more. But, at least for me, in a mono, I believe the increase of batten tension, use of flattening reef and proper luff tension... and no topping lift tension of course, took care of it but I'll need to collect more empirical data to really pin down the culprit. And tell-tales can help too. Oh and my mast has an 8 inch rake.. (no backstay tensioner) but main was built (ostensibly) with that included.... not sure how that figures in yet. I've been going through Marchaj's "Sail Performance" but still haven't found the answer although on page 238 he does say "Battens with incorrect stiffness may ruin even the best sail. This photograph shows the fully battened mainsail of a Thai Mk4 catamaran on which an undesirable tendency of the leech to curl to windward is apparent. This could be cured by increasing the batten thickness (stiffness) at the outer edge."

[Snowpetrel]

Originally Posted by Don C L

Spreader or batten?

Sorry, yes I meant batten tension. Thanks

[StuM]

Originally Posted by Don C L

Spreader or batten? Well I'll have to get out and mess with it more. But, at least for me, in a mono, I believe the increase of batten tension, use of flattening reef and proper luff tension... and no topping lift tension of course, took care of it but I'll need to collect more empirical data to really pin down the culprit.

I think that you will find that the S-Shape in light winds is a symptom of too much batten tension, not too little.

[admiralslater]

I had the same issue on my cruising main, and it was vastly improved by a leach recut .I think that it is the same issue. however it costs nothing to try the other solutions . I don't see any diamonds or jumpers in your photo so pre bending the rig may not be possible . tensioning the forestay and shrouds will not help the leach as all the load is generated through the halyard ,outhaul ,mainsheet and Cunningham.

[MC2019]

We had that exact same problem on the 42' cat I brought from Hawaii to Seattle, its blown out. Get re cut or get new.

[paxfish]

Hi Gang,

Without investing in adjustable batten caps, what are the tricks for increasing batten tension on a more classic velcro-type pocket? I need to kick it up a notch on my upper two battens, but having trouble getting the leverage to do so....