Polyester sails stretch. Sailmakers add resin to the cloth in order to stabilize the fibers. Sailmakers then cut the sail to arrange the load paths to align with the primary direction of the fibers (called “warp”). Even though sailmakers want to control these loads, stretch can still be significant, and this is not all bad. A mainsail must function from zero to 30 knots or more, both upwind and reaching. By tugging the cloth this way and that, we can stretch it and change its shape, creating a sail shape that can be adjusted for the conditions.
Sometimes a few wrinkles are created in the process. While wrinkles can plague any sail, we’re going to focus this article on the mainsail. Follow along as we explore the various factors that influence the look, and therefore performance, of your primary working sail—and what we can do about it.
It helps to understand what we are we up against. If the cloth is too heavy (or it’s constructed out of laminate), it can be difficult to create the desired fullness in light winds. If the cloth is too light, heavier wind can overpower the cloth, resulting in undesirable shapes, despite our best efforts. Eventually, most polyester sails permanently stretch into baggy shapes that no amount of tugging can adjust back into flat, draft-forward shapes suitable for sailing to windward. This won’t matter much off the wind, but the result will be slow sailing upwind. The combination of increased leeway, increased heeling, and increased drag can reduce velocity made good (VMG) by up to 35%.
Actually, there are different kinds of wrinkles and it helps to know what kind you’re dealing with.
A WELTER OF WRINKLES
Storage Wrinkles. As with clothing, they usually come out with use. If sails are repeatedly folded in the same place, wrinkles can become more permanent…so don’t do that. Either roll, flake loosely, or fold differently each time. Neat is pretty, but loose is good for the sail, which is more important. Air must circulate. Sail bags should be generous; if the bag is snug, get a larger one.
Installation Wrinkles. Many wrinkles can be resolved by tracing them to their source, like following an arrow. If they radiate from the tack or clew, sometimes the attachments are not aligned. With an attached-foot sail, the first or last slug or the slider can be higher. Can you adjust the lengths of the attachments to place them in a line? At the tack, the problem is often the outhaul pulling the tack aft, away from the mast, and the tack attachment may be too far aft. A lashing around the mast or a redesign of the Cunningham tackle can fix this by keeping the tack forward.
Headboard Wrinkles. The headboard can be too small or the hole that receives the halyard shackle is not aligned to fall under the masthead sheave, creating more wrinkles. Either move the sheave aft or drill a new headboard hole more in line with the sail slugs. This is most common with replacement sails.
Batten Wrinkles. The roach of a sail is supported by a broadseam sewn into the sail and kept in place by batten tension. Although there is some advantage to sailing with stiff, full- length battens to support the roach—especially back in the days before laminate sails—wrinkles along the battens nearly always can be linked to slow stretch of the fabric and they should be snugged up. This will help them support the roach and reduce the strain on the sailcloth, forestalling premature leech stretch.
YOUR WRINKLE TOOLBOX
Start with the tackle that adjusts your Cunningham (named after 1958 America‘s Cup winner Briggs Cunningham). If the mast is straight, the slugs or bolt-rope track is low friction, and there is no excess luff material. The halyard may provide all of the luff tension you need. On the other hand, if the mast is aggressively bent, or if the mainsail’s bolt rope goes directly into the mast groove, the friction over the height of the mast under sailing loads may prevent the halyard tension from influencing the tack. You can think of the Cunningham as evening up the luff tension along the length of the luff and also balancing mainsheet tension, so that the downward mainsheet pull on the boom is equal across its length.
To make the Cunningham effective, you will need some powerful downhaul tackle. It may attach to this reinforced grommet as much as a foot up from the tack. At a minimum, the tackle should be sufficient to match mainsheet tension.
On a dinghy, a single line pass through the Cunningham and ending in a clam cleat might be sufficient. But twelve-to-one Cunninghams on some racing dinghies are not uncommon, unless prevented by class rules.
My F-24 multihull has a 7:1 mainsheet. We have an 8:1 Cunningham downhaul, because 4:1 would not get it tight enough. This is just enough, and we have to pull hard. In fact, because it is a 4:1 cascade to a 2:1 webbing strap through the Cunningham hole, it is probably more like 7:1, with a smaller rope (1/4-in. vs. 3/8-in.) resulting in less pull. Your experience may vary.
Every time we had less power on the downhaul than the mainsheet we ended up installing an upgrade, which solved the problem. Once downhaul/Cunningham power balanced the mainsheet, the sail could be trimmed without wrinkles and a good draft-forward shape could be achieved.
Really, these are minimums. If you really intend to stretch the luff to pull the draft forward, bend a mast, or flatten a polyester sail, twice this amount is needed.
WHEN WRINKLES REALLY WORK
Ever heard of “speed wrinkles?” It’s a catchy phrase that doesn’t mean quite what it says. The wrinkles are a consequence of stretch adjustments made to the sail that create shapes that may be fast in certain conditions. A loose Cunningham downhaul, for example, pushes more cloth into the sail. Wrinkles themselves don’t help the boat go faster, but they may hurt far less than the improved shape helps.
Horizontal winkles commonly appear parallel to the boom when the halyard is eased in light winds. Stretch is reduced and the draft increases (very slightly, as we will see, for laminate sails), which adds power, which is optimal in light air. The position of the draft also moves aft. In these conditions you will likely ease the jib lead outboard just a little to prevent backwinding the luff of the mainsail and ease the sheet a smidge to increase jib fullness. The resulting shape is faster than if the halyard were pulled hard, regardless of the wrinkles you may see. Same with the jib.
Vertical wrinkles behind the luff are typically the result of over tensioning the luff of a polyester sail. If the sail was cut too full or is stretched out from use, this maybe the unavoidable result of stretching the sail into a flatter, more draft-forward shape. Not good, but not bad if there is a good reason. The wrinkles are probably inside the mast turbulence wake (assuming non-rotating, non-wing mast) and will do little harm. If the sail is baggy, you may need to budget for new sails, but really tugging on the Cunningham can help in the near term.
WHAT ABOUT LAMINATED SAILS?
Laminates don’t stretch enough that tweaking halyard or downhaul tension changes much. However, even sheet metal can wrinkle if the fit is poor. It won’t form compound curves without permanent distortion. If the edges are not pulled to the correct length the metal must go somewhere. If forced into a compound curve that was not molded in, it wrinkles and buckles. I’ve seen wrinkles in 1.5-inch plate on big oil tanks that were placed on a non-level foundation. Let’s consider these sail images as though they were metal. Some of the winkles are hard to avoid, some are fit problems we can and should fix, and some hurt nothing and might contribute to a fast shape.
What to do? You could buy a laminated sail made of any number of modern materials. LaminateD sails don’t stretch much, if at all. The latest Carbon, Dyneema, and Kevlar fibers ensure this. The downside? The shape cannot be adjusted by stretching the cloth, but with a loose foot, a rotating or bendy mast, and good sail design, there are other ways. Unless you are a very competitive racer, the shape does not change appreciably over time. The sail will stay fast to windward throughout its working life. Unfortunately, that life won’t be long. The laminate is not as UV resistant and the forces imposed by hard jibes will be many times greater, because there is no stretch. Broken gear, including traveler cars, often come as a surprise to sailors that convert to laminated sails with Dyneema running rigging. Think dollars in your wake.
Still, you have some control over sail shape, especially with polyester construction.
YOUR ACTION PLAN: TRIM FIRST
With all sails, wrinkles are always secondary to good trim. Focus on sheet tension, lead position (jib), traveler and vang (mainsail). After that come the major shape adjustments; mast bend and rotation for the mainsail and forestay tension for the jib. Then stretch (or relax) the sail to get the shape you want. Only after all of this is right, concern yourself with wrinkles. When tensioning the mainsail cloth, remember to tension downhaul first (normally with the Cunningham), then outhaul, and only then, mainsheet tension.
Even a non-stretch sail can be made slightly more full for very light conditions by pushing in more cloth (bunching it up by keep the luff very loose), but the wrinkles may be excessive for the small gains. Additionally, sometimes the sail designer takes advantage of the low-stretch characteristics of laminates to make a very light sail, with the result being it still has some stretch. But you really don’t want to be trying to stretch it like polyester, or you will overload the lightweight cloth.
Mostly, the halyard was not sufficiently tensioned during the hoist, so it can’t be fixed without releasing the mainsheet, releasing the outhaul, and then tightening the halyard. A strong Cunningham would allow tensioning the lower half of the sail underway.
You can easily see the grommet wrinkles at tack and clew. Again, the halyard was not sufficiently tensioned. Additionally, it appears that the tack is not far enough forward. As a result, grommets are taking the aft pull from the mainsheet and outhaul, creating slow wrinkles and overstraining the grommets. At the tack, the leech was meant to be straight but it is curved because the tack is aft of the mast. The tack and Cunningham grommets should all be pulled both down and forward so they can keep the leech straight, as the sail was designed.
There is also a wrinkle at the square top. The leech is falling away. The original, molded-in compound curve has been violated. Increased tension on the top batten prior to the hoist would help. The sail makers should make this section of the sail quite flat, since it functions like an airplane wing— more as a trim tab than a lift-generating section. Also, because it is behind a rotating wing mast, there is already significant camber (draft) formed by the mast section.
