A lot of us use a single roller furling headsail or genoa for just about all sailing conditions. A well-built cruising genoa will have a luff pad sewn into the sail that adds bulk in the middle of the sail, the daft area, which flattens the sail as you reef it. As you change wind angles and change the amount of sail you have rolled out, you need to adjust the sheet leads to maintain the best possible shape and the best possible performance.
The idea is to trim the headsail so the top, middle and lower telltales all stream in sync and break together when you sail too close to the wind. As you roll in a reef, you will tighten the sail’s foot and loosen the leech so the top of the sail twists off and loses power. You need to move the sheet cars forward until the leech and foot are the correct tension and all of the telltales stream and break together. Obviously, as you roll out a reef, you will need to move the sheet cars aft. It is helpful to mark the track at the normal car positions for full sail and the first and second reefs. Some boats have control lines running to their sheet cars so you can adjust the cars’ positions from the cockpit. If your boat does not have car control lines, you can add them easily.
Off the wind, you may find that your sheet cars are too far inboard to allow you to trim an efficient shape into you genoa. In that case, you can rig a second sheet from the clew to a block mounted on or near the toe rail and positioned so the telltales break evenly. Or you can rig a line that’s called a twing to the genoa sheet that allows you to haul the sheet and thus the clew outboard, thereby opening the slot between the genoa and mainsail and tightening the leech to maintain the best downwind sail shape.
Experiment with sheeting angles, sheet car positions and twings until you discover the best positions that will deliver the best sail genoa shapes in all conditions. You’ll be pleased with the sailing results.