Wrinkles

 I've sailed with polyester sails lots and understand adjustment by stretching. I understand rotating masts and bendy masts and how they affect shape. If you ease off the main halyard in light air, for example, the sail becomes for full and powerful. There are some wrinkles across the bottom, but they do little harm and the sail is faster than if you stretched it tight.

But this is less applicable  to laminate sails. They stretch, but far less, and most of the shape is baked in when they are made. For example, if I really yank on the downhaul to eliminate these wrinkles (basically balancing the mainsheet and outhaul tension) I don't expect to see much change in draft or draft position. Thus, I assume the goal is normally to reduce wrinkles, since they are not the result of any beneficial shape manipulation by stretching (or not stretching) and they will disrupt air flow. In fact, eliminating wrinkles probably takes you closer to the original design shape. Smooth seems fast.

With and without Cunningham tension. A slight difference in camera angle. but if you lay a straight edge on the battens, they are the same. Without a trial horse sailing next to me, I can't honestly, accurately say which is faster because of wind and wave variations.

 

If I measure the draft and position of draft with a ruler I see no change. It seems like sheet metal. It will wrinkle if the fit is poor or if we ask it to make a compound curve.

• Jib. When the sail is first hoisted the luff was straight. When the wind comes up the luff is curves (sags), reducing the straight line distance between between the head and tack. If we don't pretension the sail it will bunch up on the forestay. These wrinkles are primarily horizontal and don't hurt much. We need to be cautious of over tensioning the sail if there is a furler; they don't like rolling under high load.

• Main, square top. The leach is falling away, requiring the top of the sail to take a potato chip shape if there is any design fullness (broadseam). Unless the sailmakers cuts this area very flat, the molded-in compound curve is violated. 

• Mainsail, tack and sliders. Often wrinkle radiate from these (polyester too), and the cause is often that the tack or reef grommet is not tight forward, but has been pulled aft by the outhaul. Even sheetmetal would wrinkle, because you have pulled it out of square. The tack and Cunningham tackles need to pull forwards as well as down. Reef tackles too. A very common shortcoming.

While I'm sure there is some bias stretch, these specific wrinkles can exist without stretch.

The question is whether stretching a laminate sail to remove wrinkles has any material effect on shape, or whether the wrinkles are generally the result of either poor fit or incorrect installation/rigging.

(I've intentionally skipped a lot of factors for brevity. It's just a forum tickler. Mast bend. Rotation. Headboard misalignment. Forgive me.)

---

I'm ordering a new laminate main, not because I don't like my current one, but because it is showing signs of delamination. It's old but still has a nice shape. Until it blows ....