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Six Factors of Perfect Upwind Headsail Trim

It’s not news that headsail trim is more than just pulling on sheets. Quantum’s Chris Williams details the six important factors needed to get perfect headsail trim for the conditions.

There are six main variables to consider in headsail trimming: sail choice, sheet tension, lead height, inhaul, headstay tension, and sail cloth tension. Balancing these variables correctly, as well as a few other considerations, is what makes a yacht tick. I will share details on each to help both cruisers and racers perform.

1. Sail Choice

Selecting the correct headsail is typically the first decision you need to make, often before you leave the dock if you don’t carry your whole inventory with you. Depending on your type of sailing, you may not have a lot of sail options; however, it’s still important to consider. If you find you’re often leaving the dock without the proper sail, you might want to look into adjusting your sail plan and inventory. For me, if I raced all day and carried a sail I didn’t use, then I was either too conservative or made a bad call. It may seem like a small thing, but on yachts such as Melges 32s, Fast 40s, or TP-52s, an extra jib will cost at least one boat length per run. When cruising, unnecessary sails can take up valuable space and get in the way.

I use my judgment on what the conditions for my sail are likely to be. If you’re racing, check the weather every morning instead of relying on a weather report or dock talk among the crew. My favorite forecast models are the HRRR and NAM 3k models. These are short-term forecasts and give a pretty accurate forecast based on current/recent observations, but don’t rely on these for forecasts from the night before, as they’ll be obsolete by morning. Additionally, talk with your crew experts and make sure you have buy-in on the sail call for the day because once you leave the dock, you have to live with your choices for the whole day or trip. If you’re racing, communicate with the mainsail trimmer and afterguard to get agreement on which sail to start with based on wind conditions for the first beat. If conditions are changing and you need more time to make sure you have the right sail, communicate this to the afterguard, keeping in mind that in the big picture any delays to a team’s starting routine can have trickle-down effects on performance.

Some yachts prefer deeper headsails and some yachts prefer flatter headsails. Keep this in mind when making a call. For example, while a TP-52 and a Fast 40 look like similar yachts, they could not be more different in how they perform with different headsails. You must err on the powerful side of headsails for a TP-52, whereas on a Fast 40, you should err towards picking a flatter jib if you are not sure. 

2. Sheet Tension

How hard you trim a jib depends on the shape of the sail, the amount of power the yacht needs for the conditions, and the tactical mode you’re looking for. In lighter winds, you are generally looking for as much power as possible, and you can get this with a reasonably tight trim. I try to trim the jib so that the top battens’ leech telltale is stalled about 10 to 20 percent of the time. In race mode, once the crew starts hiking, you generally want the leech telltales flying 100 percent of the time. As the yacht becomes overpowered and the main trimmer starts to lower the traveler and twist the mainsail, you must start twisting the jib. Generally, wait until the mainsail starts showing signs of backwinding and then start easing the sail.

Jib sheet tension has a huge effect on boat speed. If you’re not in VMG mode upwind, it is necessary to give the jib a slight ease. This is often done by moving the lead outboard, but if your yacht doesn’t have this control, then a slight ease in jib sheet is necessary. Just don’t ease the sail so much that it starts to luff in the top half of the sail.

3. Lead Height and Position

More often than not, trimmers will err toward having the lead too far forward or too far back and the foot of the jib too flat. However, lead position is very shape dependent. If the jib is old and round in the back (a red flag that you need a new sail), you have to be careful with setting up the foot too deep, which will carry extra exit angle up the sail and you won’t be able to sheet the sail as hard. Similarly, at the bottom of a jib’s range, you can power up the foot and ease the sheet a little to deepen the whole sail. At the top of a jib’s range, you flatten the foot and trim the sail a little tighter.

Play around with lead position and sheeting angle and try to make the telltales match from top to bottom. In windy conditions, it’s okay to have the top half of the sail luffing before the bottom of the jib.
Wave conditions also affect how you set up the sail plan. If the sea is choppy, it’s best to power up the bottom of the sails and set up the twist a little more than normal. This provides a larger groove and the ability to foot off to maintain speed.

In puffy conditions it is sometimes best to just play the lead from the rail rather than coming off the rail to ease and trim the jib. If you’re not hiking, you’re slowing down the yacht. Don’t sit legs on the high side thinking about the next adjustment or waiting to make the next change!

4. Inhaul and Sheet Angle

A general rule of thumb is to carry the tightest sheet angle in lighter winds and open the sheet angle up in stronger conditions. There are no magic numbers on sheeting anglesjust think about trying to match the mainsail and the jib twist profiles as closely as possible. Larger yachts can generally get away with tighter sheeting angles than smaller yachts. But just because you see photos of TP-52s racing with two-degree sheeting angles, it doesn’t mean it will work on your boat. Try different sheet angles and learn the limits on how tight a sheeting angle your yacht can take. Some yachts need to start out wide after a tack and then slowly work the lead angle in. 

As a special consideration, try to carry a tighter sheeting angle when you’re off a start line, especially if there is a yacht to leeward. Similarly, in flat water, you can always get away with a tighter sheeting angle than in normal choppy conditions. 

Keep in mind that the sheet angle is one of the biggest throttles on the yacht. If you need to go into fast forward mode or true upwind VMG is less important than boatspeed, ease the lead outboard. Just as dropping the mainsail traveler makes the yacht go faster, the jib lead outboard speeds the yacht up. 

5. Headstay Tension

Proper headstay tension is dictated primarily by the mainsail shape. However, if your jibs are designed with a proper luff curve and the mainsail is set up to a target depth, a tighter headstay is almost always faster. Anytime you sag the headstay, you have to ease out the leech to maintain the same twist angles in the jib. Ultimately, you will have less twist as you get near the top of the headsail. The tighter the headstay, the tighter you can trim the jib and maintain acceptable twist and less return on the exit angles. Always work on how to tune the mainsail to carry as tight a headstay as possible while maintaining the appropriate power (depth and twist) in the mainsail. 

6. Jib Cloth Tension (Luff tension, halyard tension, jib Cunningham)

Luff cloth controls both depth and draft position. Some boats adjust the cloth through halyard tension while others use a jib Cunningham (tack) control. I often find that jib trimmers do not use enough cloth tension, especially as sails age. Many trimmers assume that the best set up with a brand-new sail is to have some wrinkles in the luff. That may be true if the designer nailed the shape of the sail perfectly (such as a highly refined one design sail), but you have to look carefully to make sure you’re setting up the draft in the correct location. It never hurts to take a look at the jib from the foredeck to make sure your eyes are calibrated and the draft is appropriately placed. In general, you want the draft at about 30 percent in the bottom of the jib and between 35 percent and 40 percent forward in the top half of the jib.

As sails age, you will need to carry more and more cloth tension to keep the draft forward. On modern keelboats with plenty of righting moment, the sail plan creates upwash (lifting or bending the apparent wind angle of the onset flow of wind) that allows entry angles of about 55deg relative to the centerline, even though the apparent wind angle in the middle of the sail plan is likely 20deg to 22deg (There is little relationship between the angle of the jib entry and the angle the yacht sails upwind.) The more lift a sail plan creates, the more upwash is created. To sail higher, you need to pull the traveler up high, sheet the mainsail on, and create as much power as possible without slowing the yacht down too much.

Trimming the headsail can be very rewarding. Correctly balancing these six variables should make for a yacht that is easy to sail quickly. 
 

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The Discussion

Ted Drossos

On Feb 15, 2019, Quantum’s Chris Williams wrote an article detailing the six important factors needed to get perfect headsail trim for the conditions. There is a portion in the second section about sheet tension where he discusses telltales on the leech of the jib. "I try to trim the jib so that the top battens’ leech telltale is stalled about 10 to 20 percent of the time. In race mode, once the crew starts hiking, you generally want the leech telltales flying 100 percent of the time." The example describes a jib with battens which leads me to believe that he is referring to a non overlapping headsail. I race a masthead rigged boat (C&C 110) with overlapping headsails. I don't have leech telltales on my headsails and was wondering if they would be as useful on overlapping masthead genoas as they are on a non overlapping fractional jib?

Chris Williams

Hi Ted, there are more factors with a genoa due to the spreader lengths. I think they maybe useful, but you may also find that the shrouds rip the tell tales off pretty quickly when tacking. Generally the wider the spreaders the more your tell tales will likely fly often and the narrower your spreaders the easier the tell tales will be to stall. Similarly, on some yachts, you trim the genoa very hard against the top spreader and keep trimming to pull the middle of the sail into the rig. If this is the case having a tell tale in the top will not indicate how hard you need to stretch the genoa around the rig. I imagine on a C&C 110 you don't need to sheet this tight- so it maybe worth experimenting with.

Ted Drossos

Thanks for the reply Chris. I'll try experimenting with some leech telltales this season. Maybe the rod rigging won't rip them off so quickly.

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