North Sails NEWS


What To Look For

How wide is your groove? Sounds like a question from the ‘60s, doesn’t it? In this story, North expert Skip Dieball explains the upwind groove and tells us what to look for.

Earlier this year, as part of a story called Achieving Balance in Your Sailplan, we discussed refining your boat’s upwind angle of attack. That’s another term we use to describe your upwind groove—the point of sail in which you sail against the wind most efficiently, at a consistent angle of heel. In practice, the groove covers a range of a few degrees angle to the wind in which you are able to steer consistently at a steady speed.

How your rig and sails are set will change the width of your steering groove at the start and upwind.

Depending on your set-up, the groove on your boat may be narrow, with a tolerance of only a couple degrees, or wide, in which you can head up or down several degrees. If the groove is wide, you can handle gusty winds and steer around waves better, but you won’t point as close to the wind. If it’s narrow, you must maintain a precise course, which can be a challenge in variable winds but can be very fast in flat water.

Sometimes I call finding the groove finding the “happy spot,” because that’s where, for a given condition, our blend of forward speed and pointing are as good or better than boats around us. The term also applies to how you’re feeling if your groove is too wide or too tight. Visual cues are also useful: if your telltales react too fast on both sides of the sail, the entry angle is super narrow; if the sail will actually luff before the telltales react, the entry angle is too wide.

Adjust the forestay length

If you think your groove is too wide or narrow, try changing the length of your forestay. Here’s why:

All sails are cut for a certain amount of curvature, known as luff curve. The more material in the front of the sail, the deeper it will be. Your forestay needs to be long enough to match this depth, and the way to tell is by studying how your telltales react from top to bottom when you’re sailing upwind. If they react in unison—all luffing at the same time as you head up—your forestay length (and halyard tension) is about right. But if the tell-tales in the mid-section of the sail are reacting differently from those at the top and bottom, then the forestay is not set up for the way your sail is cut.

The shorter your headstay relative to your luff curve, the flatter the luff or entry angle will be in the middle of the sail and the quicker the middle telltales will react on both windward and leeward sides. If the headstay is too long relative to your luff round, the telltales in the middle will tend to be slower to react than those at top and bottom.

In most one-design classes, you need to set the headstay length before the race and leave it.

On some boats with deck-stepped masts, you will tension up the rig at the dock, such as the Thistle, Highlander or Interlake. On these boats, the sailmaker will cut sails for a static headstay sag and you’ll need to adjust the groove by means of halyard tension. This tension is spelled out in the sailmaker’s Tuning Guide. (For more on this topic, read “Why is Headstay Sag Fast Upwind in Light Air?”)

On boats like the J/70 and Tartan Ten, with swept spreaders and a wide shroud base, you’ll set the headstay and then use shroud tension and backstay to tighten the forestay underway.

On boats with keel-stepped masts, you can chock the mast forward at the deck to create more headstay sag and add power to the sailplan. If your mast butt is movable (like the Etchells), then you can move it aft to induce more sag or forward to tighten the forestay. Keep in mind, however, when you adjust the mast butt, you are affecting the mast pre-bend too. You can also tighten the forestay with the permanent backstay and through rig tune. The Lightning, Etchells and Star fall in this category.

Change headstay tension

I think of the forestay length as the gross tune for the groove and the halyard tension on each sail as the fine tune. Once you find a nice spot for the forestay, then you can fine-tune with halyard tension. Simply put, the more tension you add with the halyard, the rounder the shape forward and the wider the groove will be. Loosen up the halyard for a softer, finer entry and the groove will get narrower.

Again, on different boats, the dynamics are a bit different. Jib-halyard tension is actually a key component on boats with deck-stepped masts and some boats like the J/70 have a fine tune on the jib halyard for this purpose. When I want a finer entry, I ease the halyard until I have wrinkles at the snaps along the luff of the jib.

When sails are newer with a harder finish or a more true shape, it’s easier to set them up. I find the range of halyard adjustment on a new sail may be only an inch or two (depending on purchase system), while it’s five inches on an older sail. Either way, it’s good to have marks on your halyards for quick reference; we color code them too—red for tighter and more forgiving, black for less tension and a finer entry.

Leech adjustment on the main

Mainsail trim changes the width of your groove, too. If you sail with an open, twisted leech, the groove will be wider and more forgiving to sail in at speed. However, you’re not likely to point as high. If you sail with a straighter, firmer leech, the groove will be narrower. You’ll be able to point higher but both helmsman and main trimmer will need to be able to react quickly to changes or you may be slow at times.

Depending on the style of boat, use of the backstay or vang-sheeting can contribute to the shape of your leech as well. Tightening the permanent backstay, if you have one, will open the leech; easing will add “hook” to it. With a deck-stepped mast or on any boat that can induce mast bend through use of the boom vang, vang-sheeting can be a powerful tool to help create a more open leech.

Taken together, the forestay length, halyard tension, and mainsail leech shape can have a large impact on the width of your groove when sailing upwind. If you’re sailing upwind and feeling grumpy, try making some adjustments until you find a happier spot. All these need to work in harmony to find the ideal upwind groove.

Connect with North Expert Skip Dieball for more information.

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