The jib and genoa are very important because they provide most of the driving force for your boat. There are two reasons for this: First, your headsail has no mast in front of it to create turbulence and spoil clean flow. Second, it sails in a continual lift caused by the main's upwash.
Upwash is the bend that a sail induces in the approaching air flow. For example, the wind begins to curve around a mainsail well before it actually touches the sail. Sitting in this upwash region, the genoa thinks it is in a lift, and consequently can be trimmed farther off the centerline of the boat than the main. This makes the genoa more efficient by rotating its forces (perpendicular to the chord line) more forward and less sideways than the main.
If your main is the sailplan's rudder, then the genoa is its motor. Of course, their functions overlap, but in general you should trim your genoa for drive and your main for helm balance.
Describing a genoa
The most obvious characteristics of a genoa are its size and shape. We measure genoas by the length of their LP, or luff perpendicular. To construct an LP, draw a line from the sail's clew to its luff, intersecting the luff at a right angle. The length of the LP divided by J (the distance from the forestay to the front of the mast) equals the overlap of the sail.
LP divided by J = Overlap (%)
On IOR boats, the largest headsails usually have a 150% overlap; No. 2s have a 130% overlap; No. 3s have a 98% overlap, and so on. Most PHRF boats are allowed 155% genoas without penalty.
The sails that are less than maximum size are used in heavier winds once the maximum amount of force for a given boat has been reached. Beyond this point, maximum sail area simply overburdens the boat, and it's better to reduce drag by changing down to a smaller jib. This will improve the lift-to-drag ratio (the best indicator of upwind performance) by holding lift at a minimum while lowering drag.
Note that smaller headsails are almost always shorter on the foot, but still nearly full hoist. The reason for this is that a high-aspect-ratio sail is more efficient. The sailmaker preserves the maximum wingspan of the boat's foils, but shortenis their width to the limits of construction technology.
Genoa Trimming Procedure
Like the mainsail trimmer, the person who tends the genoa needs a methodical approach to cover all variables and maintain fast shapes. Here is a trimming procedure that you can use when you set up your genoa. The six basic steps are:
- Determine overall power by selecting the correct genoa.
- Determine the efficiency of the genoa with the lead angle.
- Set depth and twist with sheet tension.
- Set depth and twist with the fore-and-aft lead position.
- Set depth and twist with backstay tension.
- Set draft position with halyard tension.
Step 1: Determine Overall Power by Selecting the Correct Sail
This first step isn't too tough if you sail in a one-design class that allows only one jib, but it can be perplexing on big boats with up to 14 headsails. The best way to make good sail selection choices is to keep a record of the headsails you use with wind velocities and boat performance. After a while you'll have an extensive chart as a guide.
Since your genoa determines your ultimate sailpower and the total heeling force, heel angle is a very important indicator when choosing a sail. As a rule, if your heel exceeds about 25 degrees, change down to a smaller genoa. Long and narrow boats may be able to maintain speed with a bit more heel than this, but modern fractional rigs must be sailed considerably flatter.
Helm balance is another consideration. If you have too much helm, changing to a smaller genoa might be a good idea. This relieves windward helm by reducing the angle of heel, removing sail area from the back of the genoa, and permitting the traveler to be eased further, which opens the main's leech.
Don't forget that each of your headsails is designed for a maximum wind velocity. This number (specified as true or apparent wind) should be written clearly on the genoa clew, so you'll be sure to change before exceeding that limit. Finally, if you can flog your main and maintain the same speed, it's time to depower.
Step 2: Set Genoa Efficiency with the Lead Angle
It is common to measure the angle between the boat's centerline and your genoa's sheeting base. Many new boats today are able to move their jib leads sideways as well as fore and aft, which gives them much better control over their lead angle.
A narrow sheeting angle works best for high-efficiency conditions when the hull is easily driven. Narrowing the sheeting angle rotates the sail's forces to the side, cutting down on drive and increasing heel, but letting you point higher. Though this makes the genoa more efficient, the sail is also very critical -- more prone to stall and less able to accelerate.
Sheet inboard when you have these conditions:
- Medium air
- Flat water
- Experienced helmsman
- You'd rather point than foot
- The boat is efficient underwater
Use a wider sheeting angle when conditions demand that you sacrifice some efficiency for more reliable power:
- Very strong or very light wind
- Genoa at the top of its range
- Heavy chop or sea
- Boat is inefficient underwater
- Helmsman is inexperienced
- You need to foot, not point
In summary, sheet inboard in ideal conditions and sheet outboard to play it safe at other times. On well-sailed boats, the lead angle is adjusted quite often with an athwartships jib lead puller. If your boat isn't rigged for this, use a barberhauler, a short sheet that pulls the genoa clew outboard or inboard.
Step 3: Adjust Twist and Depth with Sheet Tension
The genoa trimmer's primary responsibility is to maintain optimal sail shape as wind velocity and other conditions change. More than any other control, sheet tension must be adjusted to preserve the same basic trim.
The trimmer's secondary responsibility is to help the helmsman steer the boat. For example, he should ease the sheet for big waves or sudden lifts, and trim for flat spots and headers. Then, as the helmsman brings the boat back up to speed and on the wind, the trimmer must slowly re-trim the sheet. All this requires constant communication to make it work properly.
Trimming the sheet affects the genoa in several ways. It reduces twist, reduces depth and narrows the sheeting angle all at the same time. These changes combine to let you point higher. Easing the sheet has the opposite effect -- more speed and less pointing ability.
As a guide for proper sheet tension, observe how far the genoa is from the upper spreader and from the chainplates. We cannot prescribe these exact distances without knowing more about your boat and the conditions you're sailing in. These are measurements you'll have to get (and add to your sail data) through trial and error.
Step 4: Set Twist and Depth with Fore-and-Aft Lead Position
The fore-and-aft position of the genoa has a significant effect on twist and depth in the foot. Remember that twist is the change in chord angles (relative to the centerline) from the foot to the head of the sail, and is necessary because of wind twist aloft due to gradient and sheer.
When sail twist matches wind twist, the genoa is perfectly trimmed from top to bottom. Now the sail should luff simultaneously up and down the luff when you head up slowly past close-hauled. Set your lead position by luffing up slowly and watching your tell-tales. The windward telltales should 'break' evenly from top to bottom at the same time.
If the top telltales flutter before the bottom, the sail is twisted too much. Move the lead forward to pull down on the clew, increase leech tension and reduce twist. If the bottom telltales luff first, the sail needs more twist. Move the lead aft to relax tension on the leech, allowing the clew to rise and the sail to twist.
Moving the genoa lead position also affects foot depth, much as the outhaul controls foot depth on a mainsail. To add depth, move the lead forward. This shortens the distance from clew to tack, and moves the foot of the sail farther away from the chainplates. (The upper two-thirds of the genoa will keep about the same shape.)
Use your Sailscope to measure the depths of your sail at each of the three draft stripes (the middle one is most important). The table in Figure 12 gives approximate target depths for the various genoas. Note that the depths do not vary too much from sail to sail. The acceptable range of genoa depths is actually quite narrow. (If your boat has an unusual sailplan, hull shape or sheeting angle, these suggested depths may not work for you.)
Step 5: Adjust Depth and Twist with Backstay Tension
The backstay (masthead rig) and running backstay (fractional) affect depth in the middle and upper genoa sections by controlling headstay sag. To a lesser extent, they affect twist.
When you have power-hungry conditions (light air, choppy water) you need a deep sail. Sag the headstay by easing off backstay tension. This adds depth to the genoa as the luff moves closer to the leech. On a fractional boat, ease the running backstay for the same purpose.
The added depth will be noticeable in the upper half of the sail where the sag is large relative to the chord length. Also, sag will add depth mainly to the front of the sail, making a rounder entry and a more forgiving shape.
In light air, take care to ease the backstay enough to actually increase sag and fullness, especially in the lulls. Light-air backstay tension should be about 25% of maximum. You'll know it's too loose when the luff snaps and curls like a spinnaker.
To check sag visually, sight up the forestay from the tack while someone plays the backstay. You'll notice that gusts automatically add a lot of sag. This is exactly the opposite of what should happen. When a gust hits, you want to flatten the sail and depower it.
Your backstay will need a lot of range and power simply to counteract undesirable sag, let alone lessen sag as the wind strengthens. For each of your genoas, you'll have to adjust the backstay quite a bit to change the sail's shape from the low to the high end of its wind range.
The nice thing about fractionally rigged boats is that the runners are so easy to play. Consequently, they should be adjusted continuously, in concert with the genoa trimmer and helmsman, to keep the boat sailing as fast as possible.
Twist -- Besides adding depth, headstay sag adds power by reducing twist. It does this by letting the luff drop slightly to leeward, which rotates the leech slightly to windward. This is fine for medium air and a chop, but disastrous in a breeze because it adds power where it contributes most to heeling force -- at the top of the rig. In these conditions you need a tighter headstay to open the leech and depower the sail.
Step 6: Set Draft Position with Halyard Tension
Draft position in a genoa is controlled primarily with halyard tension. This works a lot like the cunningham -- more tension moves the draft forward and less moves it aft. Be sure to put a reference mark on each halyard (as described in Preparation) so you can compare and duplicate settings.
Use your Sailscope to locate the position of maximum draft on each of your draft stripes. For No. 1 genoas, draft position should be roughly 45-47%. Refer back to Figure 12 for some rough draft position targets for each headsail.
A draft forward shape (40%-45%) is more forgiving than a draft aft shape (47%-50%). Move the draft forward when you need a wider groove, such as in a chop or with an inexperienced helmsman. Move draft aft in ideal conditions (i.e. smooth water and medium air) for maximum pointing ability.
The "groove" -- Let's examine the importance of draft position a little more closely. What do we mean when we say a draft-forward sail is more forgiving and has a wider groove?
The groove is that optimal combination of sail trim, boatspeed and pointing ability at which your boat comes alive. We're always searching for the groove when we sail upwind (and downwind).
We can make the groove easier to find by increasing halyard tension or headstay sag to make the genoa more draft forward. A draft-forward shape is more forgiving because it's harder to stall. In other words, the helmsperson can make wider course changes and still keep flow attached on the leeward telltales.
The disadvantage to widening the groove is that it harms your flat-water pointing ability. So the groove should only be wide enough in each condition for the helmsman to control the telltales with the helm.
Telltales -- The genoa trimmer's most useful trim indicators are telltales placed along the luff of the headstay. The leeward telltales should always flow aft. If they hang limp, the sail is stalled, and the trimmer should ease the sheet immediately to reattach flow.
It's important for the trimmer to help the helmsman respond to changes in the wind. The trimmer can react faster than the helmsman, especially in light air when the boat turns slowly. If the helmsman tries to hurry by jamming the tiller hard over, the rudder will brake the boat. He has to let the sails turn the boat. If the sheet is eased first, it will help the helmsman head up slowly, and the jib can be re-trimmed in concert. This maintains the best speed.
Reaching Without a Spinnaker
Trying to sail fast on a close reach can often be frustrating. If the wind angle is too far forward for a spinnaker, it's very hard to find a good lead for the genoa. You need a special set of tracks suspended two feet to leeward of the gunwale.
Here are the problems whenever your apparent wind is in the 35 to 65 degree range:
- Your hull is too narrow to provide an ideal sheeting base.
- The genoa twists excessively when eased.
- Moving the lead forward to reduce twist adds too much depth to the genoa foot.
Your first move should certainly be to move your jib lead out to the rail, and forward somewhat from its upwind position. Unfortunately, there is not always much more you can do. Unless you carry a special reaching sail, you'll just have to wait for the wind to go aft so you can set your chute.
When Your Genoa Gets Old
Sooner or later, all your genoas get old. They drag across the rig a few hundred times, get stuffed into under-sized turtles and maybe get used in a little too much. Aging is inevitable and, unfortunately, so is the fact that some of these sails will have to be used for racing. What can be done to give an old sail a fighting chance?
First of all, it's important to understand that, compared to a new sail, an older genoa is more draft aft; further away from the rig; flatter in the forward sections; fuller overall; and tighter leeched. When you put all this together you have a slow sail, unless you take a few counter-measures:
- Trim the foot harder (closer to the chainplates) to bring the upper part of the sail closer to the spreader.
- Use more halyard tension to pull the draft forward so you have a rounder entry (with a wider groove) and more power.
- Increase the lead angle slightly to reduce main backwinding caused by roundness near the leech.
- Move the lead back slightly to twist the leech more.
As with the main, take pictures of any headsail you think could be improved, and show these to your sailmaker. It may be possible to bring the sail back to life with a bit of inexpensive surgery.