Headsail Sheeting

Many seperate details make a boat close-winded, but one critical factor often overlooked is the headsail sheeting setup. The most exquisite hull form with the most modern rig in the world won’t sail well to windward if the headsails can’t be trimmed in close enough to get the sails to do their work.

Headsail sizes are defined in terms of their luff perpendiculars (LP) as a percentage of J—the horizontal distance from the headstay’s intersection with the deck or rail cap, whichever is higher, to the base of the mast on deck. A basic headsail inventory might include a 70-percent or 80-percent blade jib, a 110-percent or 120-percent heavy-air genoa, and a 150-percent light-air genoa. The maximum practical headsail size is usually around 170 percent. Any sail over 150 percent becomes increasingly difficult to tack. It also becomes nearly impossible to sheet in properly from anywhere on deck, because the lead needs to be so far aft.

The sailplan drawing at right shows how two sails are laid out, in this case an 80-percent blade jib and a 150-percent genoa. To begin the process, the designer or sailmaker draws a pair of lines at right angles to the headstay whose lengths are 80 percent and 150 percent of J. Next, a line is drawn parallel to the headstay at the aft end of these two perpendiculars. These lines define the possible positions of the clews for the two sails. The desired positions of the tack and head for each sail are then marked on the headstay, and the designer measures 40 percent up the luff of each sail and makes a tick mark. This mark (which can be as high as 45 or even 50 percent for a high-clewed jib) determines the forward end of the proper fore and aft sheet-lead line for each sail.

On the deckplan, note how guidelines have been drawn at a 7-degree and 10-degree angle radiating from the headstay chainplate. These angles represent the range of ideal sheeting angles for the two sails while sailing close-hauled. Sailing in light air requires about a 7-degree sheeting angle for maximum performance on standard headsails. A 10-degree angle is acceptable, but the boat will not be as close-winded. Heavier-air sails, like a heavy-air 110, are usually sheeted a bit freer than 7 degrees—say, 9 degrees—to open up the slot between the main and the headsail.

Note how the 7-degree sheeting angle for the 150 is nearly off the back of the boat. This is common and, again, a big reason why a 160- or 170-percent genoa is seldom practical. The genoa track has been laid out in plan view so that it crosses the 7-degree guideline. It also extends aft of this point and forward of the 10-degree intersection point to allow a range of trim adjustment options for different sails and different courses.

To establish the clew position for the 150, draw a perpendicular line up from the intersection of the 7-degree guideline and the genoa track on the deckplan to the deck on the sailplan. Then, draw a line from this point to the 40-percent tick mark on the luff. This line defines the correct sheet lead. To complete the sail, connect the upper and lower luff tick marks to the intersection of the sheet-lead line and the parellel 150 percent of J aft of the headstay. You’ve now got a 150-percent genoa that will sheet properly.

The blade jib is laid out in the same way. However, blade jibs and staysails can be sheeted in a bit tighter, up to 6 degrees, though 7 degrees is generally fine. On the deck plan, the blade jib is sheeted to a radiused traveler on the roof of the deckhouse. This allows the jib to be self-tacking and permits traveler control to tweak the sheet lead in and out depending on course and wind speed.

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