How to Set the Jib Lead for Optimum Sail Performance

Telltales are also an important aid when determining how jibsheets should lead from the clew of the sail to a winch in the cockpit. On almost all sailboats, jibsheets are led through blocks on tracks on the starboard and port sides of the deck. These adjustable leads determine the shape of the jib. When the block is too far forward, the foot of the jib is too loose and the leech is too tight, because most of the pull on the jib sheet is downward. When the block is too far aft, the foot is stretched too tight and the leech is too loose because of the backward pull.

What you want is a compromise between the two extremes to avoid distorting the sail. There should be an even flow of air on both sides of the sail at all levels along the luff If the lead is too far forward, the bottom of the sail will have a big curve in it and the lower part of the sail will luff first. Conversely, if the lead is too far aft, the leech will be loose and tend to fall off at the top of the sail, causing that part to luff first. So the test to determine proper jib lead placement is to head the boat up slowly until the jib begins to luff If it luffs at the top first, the lead is too far aft. If it luffs at the bottom first, the lead is too far forward. But if it luffs the full length of the sail all at the same time, the lead is set in the right spot.

Telltales also allow you to determine if any part of your jib is stalled. If the bottom leeward telltale flutters first, the bottom of the sail is stalled. The sail is too flat at the bottom because the jib lead is too far aft.