A headsail is any sail set forward of the mast – on a sloop, any sail set on or near the headstay. Jibs, genoas, staysails, storm jibs and code zeros are all headsails; spinnakers are set forward of the mast too, but sailors and rating rules treat them as a separate family. The experienced sailor knows that on most cruiser-racers the headsail is the primary engine upwind, that it controls the airflow over the mainsail as much as its own, and that choosing the right headsail for the conditions is half of sail trim.
Types of Headsail
Headsails are named by size and purpose. A jib is a headsail whose clew does not overlap the mast; a genoa is one that does, with its clew reaching aft of the mast. Racing crews number their headsails from largest to smallest – the number one is the biggest genoa, the number three a non-overlapping jib, the number four a small heavy-air jib. A yankee is a high-clewed headsail set on a cutter above a staysail; a staysail sets on an inner stay behind the headstay; a storm jib is a tiny, very heavy headsail for survival conditions. A code zero is a large, flat reaching sail on a furling torque rope, measured as a spinnaker under most rules but used like a headsail.
How Headsails Are Measured
Headsail size is described by the LP, the luff perpendicular – the shortest distance from the clew to the luff. Dividing LP by J, the base of the foretriangle from the forward face of the mast to the headstay at deck level, gives the overlap percentage: a 100 percent jib has an LP equal to J, a 135 percent genoa an LP of 1.35 times J, and a 150 percent genoa is the classic masthead-rig light-air sail. The height of the foretriangle is I, measured from the sheerline to the headstay’s intersection with the mast.
Why the Headsail Drives the Boat
Upwind, the headsail meets clean, undisturbed air while the mainsail sits in flow the headsail has already bent. The headsail’s leading edge is the most efficient part of the whole rig, and the gap between its leech and the mainsail – the slot – accelerates and straightens the airflow onto the main’s lee side, letting the main be trimmed harder than it could be alone. A well-set headsail therefore adds more than its own drive; a badly set one, sheeted too hard or too full, backwinds the mainsail and slows the boat. This interaction is why sailmakers design a genoa and mainsail as a pair, with the genoa’s leech shape matched to the main’s luff.
Construction from the Sailmaker’s Bench
A cruising genoa is typically cross-cut woven polyester, with the cloth’s strong fill direction running across the panels to take the leech loads, a UV cover on leech and foot for life on the furler. A performance headsail is more likely to be a radial laminate or a load-path sail such as UK Sailmakers’ Tape-Drive®, Titanium™ or X-Drive®, where high-modulus tapes run from the clew to the head and tack along the calculated load lines over a light film-and-scrim base. Load-path construction matters more in headsails than almost anywhere else, because the clew loads are enormous and any stretch in the leech shows up immediately as a fuller, more closed sail that heels the boat and slows it.
Cruising and Racing Perspectives
The cruiser usually carries one furling genoa of around 130 to 140 percent as a compromise across the wind range, rolling it partly away as the breeze builds and accepting a loss of shape in return for convenience and safety. The racer carries an inventory – light and heavy number ones, a number three, a number four, a storm jib – and changes headsails as the wind moves through the crossover points, each sail flat or full according to its range. Both agree on the trim fundamentals: halyard tension to set draft position, sheet tension to set depth and twist, car position so the telltales break evenly up the luff, and headstay sag to set the entry.
Frequently Asked Questions about Headsails
What is the difference between a jib and a genoa?
A jib does not overlap the mast; a genoa does, with its clew extending aft of the mast. Both are headsails, and the terms are sometimes used loosely for one another.
What size headsail should a cruising boat carry?
For a masthead-rigged cruiser with a roller furler, a 130 to 140 percent genoa is the usual all-round choice. Fractional rigs with big mainsails often do well with a 105 to 110 percent jib that furls cleanly.
Can I use a partly furled genoa as a heavy-weather headsail?
For a while, and a foam luff helps, but a genoa rolled to a third of its area is full, draft-aft and high-clewed, and its sheet lead is wrong. For real heavy weather a dedicated storm jib or heavy jib sets far better.
The headsail is the front of your engine and the shape of your day upwind. Know its size and its range, keep its luff and leech in shape, and match it to the mainsail behind it, and the boat will point and go in a way no amount of mainsail trim alone can deliver.