A jib is the triangular sail set forward of the mast, its luff attached to or hoisted along the headstay, its tack at the bow and its clew trimmed by a sheet on each side. The beginner needs to know that the jib is the smaller headsail, the one you see on almost every sailing boat, and that it works together with the mainsail to drive the boat to windward. The experienced sailor draws the line more precisely: a jib has an LP of about 100 to 110 per cent of J and does not overlap the mast, whereas a genoa does. On modern fractional rigs the jib is often the only headsail, and it does a great deal more than help the mainsail; it shapes the airflow over the whole rig.
Anatomy of a Jib
The three edges are the luff along the headstay, the leech running from head to clew, and the foot along the bottom. The three corners are head, tack and clew. A hanked or luff-tape jib carries a wire or rope luff and a head pennant; a furling jib has a luff tape sliding in the foil, a UV strip along leech and foot, and often a foam or rope luff pad to keep the shape acceptable when partly rolled. Leech and foot lines control flutter. Battens, when fitted, are short leech battens on a non-overlapping jib; a fully battened jib is unusual because the battens would foul the mast when tacking unless the sail is truly non-overlapping.
How the Jib Works with the Mainsail
The jib does two things. It provides drive in its own right, generating lift as a foil with the luff as its leading edge, and it conditions the flow over the mainsail. Air passing through the slot between jib leech and mainsail luff is accelerated and bent, and the upwash ahead of the mainsail lets the jib itself point higher than it could alone. That is why a boat sails noticeably better with both sails than with either one on its own, and why a jib leech trimmed too tight, closing the slot, makes the mainsail luff backwind and the whole boat slow. Sail designers talk of the two sails as a single system and shape the jib’s leech to match the mainsail’s luff curve.
Trimming the Jib
Halyard tension positions the draft: more tension pulls the draft forward and rounds the entry, useful in a breeze and chop; less tension lets the draft move aft for pointing in flat water. Sheet tension controls twist and depth together, and the jib lead position along its track decides how the sheet load is shared between leech and foot. The telltales on the luff are your feedback: streaming on both sides means the flow is attached; the windward ones lifting means you are too high or the sail is too flat forward; the leeward ones stalling means too low or too much sheet.
Cruising and Racing Perspectives
Cruisers mostly live with one furling jib or genoa, and the jib’s virtue is that it is manageable. A 100 to 110 per cent jib on a modern boat with a big main rolls away easily, tacks without drama and does not need a grinder. Self-tacking jibs on a curved track take even that job away, at the cost of some sheeting control and drive off the wind. Cruising jibs are built with reinforced clews, UV covers and a foam luff so they keep a usable shape half rolled, and the leech is cut with a little hollow to avoid flutter over thousands of miles.
Racers see the jib as a precision instrument. A racing programme may carry a light, a medium and a heavy jib, each designed for a wind range and a headstay sag, and each with its own lead position and inhauler setting. Non-overlapping jibs let a crew tack at will, so tactical freedom improves. The sailmaker’s work is in the entry angle, the leech profile and the cloth’s stretch behaviour under load, because a jib that changes shape as the breeze builds is a slow jib. Rigs are tuned around the jib: headstay tension is set for the sag the jib was designed with, and the mainsail is shaped to match.
Frequently Asked Questions about Jibs
What is the difference between a jib and a genoa?
Size, expressed as overlap. A jib’s clew does not reach past the mast, so its LP is roughly 100 to 110 per cent of J; a genoa overlaps the mast, with LPs of 130 to 155 per cent. Both are headsails set on the headstay.
Can I reef a jib by furling it?
Yes, and most cruising jibs are built for it, but a rolled sail becomes fuller and the draft moves aft. A foam or rope luff pad, a flatter design and moving the sheet lead forward as you roll all help. For more than about a third rolled away, a smaller dedicated jib is better.
The jib is a small sail with a big job. Trim it as part of a pair with the mainsail, respect what its cloth can and cannot hold, and it will point the boat higher and take you to windward with less effort than any other sail aboard.