How to Shape the Mainsail for Beating 

Thanks for your comments.

Thanks for your note.

Hi, thanks for that explanation. Having the traveller to leeward reduces twist. The boom vang can also be used to reduce twist by pulling it on.

Healing is good. Heeling is less good.

Thanks for your note.

Glad it helped!

Cameron, no set specifics on traveler settings. Indeed, all boats will be unique. These are pretty basic settings for cruising. Moderate winds amidships; super light air, set the car a few holes upwind, but check the uppermost batten to ensure it stays parallel or slightly open. This will help the light winds exit the leech without turbulence. In high winds, you really need to have the traveler downwind to open up the angle of attack and depower the rig. For reaching or running, same traveler settings apply. As soon as the end of the boom gets out over the water (close reaching or deeper), the traveler loses effectiveness (unless it's a mid-boom traveler). Set the boom vang with moderate tension to keep the boom horizontal and the leech under control.

David, take a look at this photo: www.skippertips.com/Top-Batten-Parallel-to-Boom.jpg This mainsail has nice twist, and all of the leech telltales are flying, which means we have good sail trim. The end of the upper batten (these are full-length battens, so concentrate on that part near the leech) is almost parallel to the boom.

Jacob, thanks for your comment!

Kate, in all three illustrations, you are looking at the windward side of the sail, which faces the wind.

@@skippertips ok thank you. And what angle is the twist?

Kate, there is no specific angle, it's all done by eye and the feel of the helm. The sailor uses the helm (wheel or tiller) to tell if the adjustment produced the desired outcome. When you twist the mainsail, you want the helm to remain light (so you do not have to fight the wheel or tiller to keep the boat on course) and the boat to sail with less heel. Less heel provides a faster boat and more comfort for the crew.

@@skippertips Ok thank you so much!

The mainsheet trims the leech as long as the boom stays over the boat. When the end of the boom moves to the edge of the boat (i.e. on a close reach), you start to lose downward pull on the leech. Set the vang and keep it set on reaches and on runs. Otherwise the boom will lift and the leech will twist too much.

Captain John's Skipper Tips I finally understand. But one last question With the correct setting of the traveller and mainsheet on a given condition, do you ease the mainsheet or move the traveller when you have to change angle of attack in the sail?

Ease the traveler car first. That way, the leech stays set as you open the angle of attack. Then, if you need to depower more in high gusts or when overpowered, ease the sheet to twist the main.

No worries; I have taken beginner's classes and picked up on new techniques or even discovered I'd been doing something wrong. My philosophy is to never stop learning, innovating, testing, and trying something new. See what works and doesn't work. It's part of the deal; it's part of sailing and boating in general.

You might consider getting at least one row of reef points installed on your mainsail. I did this, even with my little 14-foot O'Day Javelin and 18-foot Cape Dory Typhoon when I owned those boats. This modification will help you keep the boat more level and the helm more balanced in gusty winds. Talk to your sailmaker to get further advice.

The mainsail leech needs to be trimmed so that the uppermost batten remains about parallel to the boom. In position #2, you are sailing in super light winds. You might set the traveler car slightly to windward. After you do this, sight up the leech and ease the mainsheet just enough to trim the leech as described above. In heavy air, ease the traveler downwind (to leeward). This opens the slot between main and jib to help depower the boat. You can depower further by easing the mainsheet in the gusts. In heavy air, your objective will be to reduce heel and weather helm to keep the boat balanced, on her feet, and driving forward.

Breal, yes, but much more. Racers really do not have time to peak up from the underside of the boom. They use mainsail leech telltales. I have not done a vid on this, but its on my schedule. Main leech telltales are installed in the upper, middle and lower part of the leech (adjacent to the battens). When beating (close hauled), you want all streaming straight aft. If you over-trim the main, the upper leech telltale will disappear to the leeward side. You need to add more twist (ease the mainsheet) until all telltales stream together. If you under-trim or have too much fullness (i.e. outhaul), the lower leech telltales disappear to the leeward side. Or, if you believe you have the main trimmed properly and the lower telltales disappear, your slot (between headsail and main) could be too open. Sheet in the jib / Genoa and see if that makes a difference.

Lucas, the top batten will not be directly over the boom, but should still look parallel. Take a look at this image of a well-trimmed main. Note all leech telltales are streaming, which indicates smooth flow off the leech (minimum turbulence). I've placed two arrows which are parallel to one another at the uppermost batten and the boom: www.skippertips.com/Top-Batten-Parallel-to-Boom.jpg

Nelson, leech flutter happens when the tabling along the leech stretches. It's pretty common in all mainsails, in particular older mainsails. But all mainsails--those used for racing or cruising, need a leech line installed. It's a light piece of parachute like cord sewn inside the leech tabling that runs from the head to the clew. There will be a small clam cleat or similar adjustment point installed near the clew. This is a fine adjustment, so use just enough leech line to stop the flutter. Take care not to cup the leech. Just put the flutter to sleep and your mainsail will flog less.

Not needed when beating. The boom is over the boat and the mainsheet handles leech control. The vang takes over when reaching or running.

My vang has a powerfull spring so I release the vang to set the boom angle and get the correct twist and then set the mainsheet and traveller.

@@PreacherRock1 There's little mention here of what one wants to do. As far as the mainsail goes, a flat mainsail works best in very light air. Depending on the boat, you want more power - more curve - in the mainsail above 6 knots. Depending on the boat, it starts to get over powered as the breeze freshens - lets say 12 knots. To reduce the power, you apply the back stay, which bends the mast. This bend stretches ie pushes the mainsail forward, which reduces the curve in the mainsail, which reduces its power. Its like when a plane takes off, its wings have a deeper shape with its flaps out, than when it's going fast, when the wings have no flaps and its shape is flat. When you bend the mast to flatten it, you also need to pull in or tighten the outhaul on the boom, and also tighten the cunningham eye. While the sail is then "bigger", its flatter in shape and hence less powerful. So you want a flat mainsail the harder the wind gets. Twist allows the top of the sail to loose power before the bottom of the mainsail does. This is almost like automatic sailing. Have the boom to leeward de-powers the sail - eventually the sail will not drive the boat at all and the sail will be heavily effected by the jib. Then its time to reef. But operating a boat bu constantly playing traveller is hard work. Good sailors alter the sail's power all the time. If short handed or cruising, twist makes one's job a lot easier. It is obvious though - the further the boom is to leeward, the less twist the sail will have. And don't forget the role the boom vang can have - its common for many boats to control twist with a powerful boom vang. Don't forget to ease the boom vang and the backstay when going off the wind.

Those positions are where twist begins, not the amount of twist. In light air, a flatter sail makes it easier for the wind to adhere to the sail. As you sight up the leech, ease the mainsheet just enough so that the uppermost batten becomes parallel to the boom or open the batten to leeward just a tad. This will help keep the sail from stalling.

John, these are subtle changes in the twist of the leech. Also see this video on trimming the leech, using leech telltales: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-eqjaEX5cS5U.html

Shane, where do you see an issue with these settings?

In short, where you need more power, less twist is good, and you can depower by allowing more twist. Light air: line up the leech so it’s a blade of a sail, pulling in good trim from top to bottom (unless you suspect there’s wind sheer up at higher altitude, then allow some twist) Medium air: do all the usual backstay, Cunningham, outhaul adjustments, and then start to allow twist at the top. The foot stays powered up, and you start to depower the main more at the top of the mast (the top of the fulcrum) This is important to keep the lower sections of the boat powered up to push through chop as it begins to form in moderate wind. Heavy air: Reef! But even with a reef, allowing the head to fall off will depower the sail higher up, causing less heel, but still keep the foot powered up to drive through challenging waves/chop. I even sometimes keep a fat foot on the reef if the waves are really big so that the boat has more pushing-power low down on the mast. I understand there’s a strategy of “vang sheeting” and I’ve seen it work quite well. It’s your instruction for heavy air. That said, it does not open the slot between the main and jib, but rather closes it down. This may result in less power, but also often times less pointing ability as the wind gets backed up in the slot, and won’t bend around the forestay as favorably. There are other ways to do it, and tons of opinions about what works best. I found the above most reasonable after reading Arvel Gentry’s article “A Review of Modern Sail Theory”, racing numerous races around San Francisco Bay over the years (it blows 25 in one part of the bay and then 10 just around a corner, so lots of changing gears), and learning from a Dad who’s done a good number of thousands of miles racing offshore. I’m definitely not saying anyone should do it the way I’m talking about above if you don’t want to, but just that I disagree and why.

Shane, thanks for your thoughts.