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.
 
Adjusting the halyard is a less effective technique for genoas built from Mylar or KEVLAR®, because the material doesn't stretch as much. With these sails, you have to rely more on headstay sag to control draft position. You should tension the halyard just enough to remove most of the horizontal wrinkles. 

© North Sails
Use your Sailscope to locate the position of maximum draft on each of your draft stripes. (Refer back to Step 3 for 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) to give your boat 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).

© North Sails
We can make the groove easier to find by increasing halyard tension or headstay sag to make the genoa more draft forward (see right). A draft-forward shape is more forgiving because it's harder to stall. In other words, the helmsman can make wider course changes and still keep flow attached on the leeward telltales.
The disadvantage of 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 leeward telltales should always flow aft. If they hang limp, the sail is stalled, and the trimmer should ease the sheet immediately to re-attach flow.

© North Sails
© North Sails

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.

DuPont and Kevlar are trademarks or registered trademarks of E.I du pont de Nemours and Company.

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