S-Shape in Main going upwind. Why?

[thinwater]

Blown out. This is my main before replacement:



And after:



Stiffer battens can help for a while. This looked just like "45" before the battens were changed, but in a few years it was sagging again.

[Pieter]

I have had this in light winds as well on my FP40ft. To me it seems indeed that the battens are for these light winds too tight. I overcome by actually push de traveller a bit windward.
Good luck and sail on..
Pieter
SV Lumina
Lumina Charters – Brazilian Coastal Catamaran Sailing

[wolfesmy]

Just keeping it simple. Is your topping lift/boom kicker holding up the foot. make sure your vang can pull the boom down.
Also you don't note the wind strength. In light air over compressing the battens can cause this effect. Does it do the same thing in 15 kts+?
Foresail back winding usually affects the main closer to the luff and not near the leach.

[Sail IC]

I'm with thinwater. Its unfortunately blown out.


Even if the S-shaping is an easy fix, the main has most likely also the same problem as the old 45 sail. The draft is too far forward and the sail is too full. Your slot is probably choked (too tight), which is bigger performance preventer than the s-shaping. This is much harder and extensive fix so it doesn't make sense to do. Maybe recut the luff curve (less) would improve it to some degree, but it depends of how the sail is designed.


Your main is also probably twisting too much. If continue sailing with it, you might want to try to pull up the traveler to windward even when the breeze is up.

[savoir]

Great post thinwater. Your pics show the exact same problem on another boat. A leech seam take up is the only solution. That should last 1 or 2 summers and then a new main is the only thing for it.

[davecalvert]

This is a classic issue with multihull mainsails not having stiff enough battens and material too stretchy for the job,
Stiffer battens will help. But, the cloth may still not be up to the job and stretch too much when the breeze is up.

[knockabout]

loosen off eccept for main halyard and main sheet /don't sail too close watch the natural set of your sail/ slowly trim til there is a slight wobble in the luff /sometimes its easier to furl the head ease the main sheet and steer the boat to fill the sail then fix the helm and steer by moving the main till you work out the most powerful main trim position/then unfurl the head and trim to suit the main /by this time you are ready for lunch and hand over the helm with instructions to steer to keep the sails full .

[Scaramanga F25]

First, I would ease the tension on those lower battens.

Also, is that a topping lift that has not been released?

[sailjumanji]

Make sure topping lift is loose, batten tension correct, and luff tension correct. If all of the above right, then sail material is stretched/blown out. A recut might fix for a season - depending on how much you sail. But once the material has gone bad it's just going to recur. Time for a new sail.

[davecalvert]

There has been a lot of good ideas on mainsail trim here but, if the sail cloth is too stretchy or the battens too soft, not much will help.
We see this often with multihull mains with a lot of roach and soft battens or material not up to the job. This can also be seen with the leech blown out.
We call this the "S" shape main. The sail stretches when the wind increases causing the luff area to be fuller and rounded and the leech falling off to leeward.
Stiffer battens would be the first step. But, I feel this only may help to a point.
If the sail cloth is too light in weight or just too stretchy, (a lot of mono hull sail makers use cloth too light) the S shape may return in more wind even with stiffer battens.

[makana]

Dave is spot on, this was a classic problem with the first rotating batten sails on windsurfers back in the late 80's early 90's. Not stiff enough battens and wimpy sail cloth.

[pete33458]

It looks like too much batten tension to me. pete

[thinwater]

What Dave said. I've been tuning sails for 35 years, fooled with batten tension and even changing battens (actually, I added carbon fiber to the aft 70%), and at some point it's done. Heck, we used to adjust batten tension between races, but not to solve that.

[Franziska]

Thinwater great idea with the carbon I might just do that, add a layer of carbon aft and taper that out towards the center.

Thanks.

www.ladyrover.com

[davecalvert]

Adding strips of carbon and epoxy resin to soft battens will certainly stiffen them up. But, if the whole batten is too soft, and the sail is getting a "S" shape,
it would be best to stiffen the full lengths. Too soft battens make the luff area more rounded and do not support much roach in the leech.
Also, on a mainsail for a fixed rig, (non rotating mast) the maximum draft should be close to the center of the mainsail. This is because the "attached flow" starts well behind the mast. In most cases non tapered battens work best on fixed rig mainsails. The inexpensive solid round non tapered battens offer good stiffness for the weight.