The outhaul is the control line that pulls the clew of the mainsail aft along the boom, tensioning the foot and setting the depth of the lower third of the sail. Ease it and the foot goes slack and the bottom of the sail bellies out with power; haul it and the foot stretches flat and the sail becomes a thinner, more efficient foil for pointing in a breeze. That is the beginner’s version, and it is enough to start with. The sailmaker adds that the outhaul does its clearest work on a loose-footed mainsail, where the foot is attached only at tack and clew and the whole lower panel responds to it; on a sail with a bolt rope in the boom groove it acts more on foot tension and the shelf than on the shape above. It is also the most neglected control on the average cruising boat.
How the Outhaul Works
The clew of the mainsail is attached to a slider or car on a track along the top of the boom, or simply to a shackle at the boom end on older boats. A line from the clew leads aft to a sheave in the end of the boom, runs forward inside the boom through a purchase of two to six to one, and exits near the gooseneck where it can be cleated or led to the cockpit. On small boats it is a single line and a cleat; on larger boats the clew loads in a breeze are substantial, and a decent purchase or a small winch is needed to adjust it when the sail is full.
The outhaul does not work alone. Foot depth is one part of overall mainsail shape, and it interacts with the halyard and cunningham, which set luff tension and draft position; with the vang and mainsheet, which set leech tension and twist; and with mast bend, which governs depth in the middle of the sail. The clew must also be held down to the boom by its strap; if it lifts, the outhaul cannot do its job.
Trimming With the Outhaul
Think of the outhaul as a gear lever for the bottom of the sail. Upwind in a fresh breeze, pull it hard so the foot is tight and the lower sail flat; this reduces heel, opens the lower leech slightly and lets you point higher. In light air and in a lumpy sea where you need power to punch through waves, ease it an inch or two so the foot develops a curve and the lower sail deepens. Off the wind, ease it further still, since a deep foot adds projected area when pointing is irrelevant. Coming back on the wind, haul it before you sheet in, because it is far easier to tension a foot that is not yet loaded.
Mark the boom with tape at your usual settings so the crew can reproduce ‘light’, ‘medium’ and ‘heavy’ trim without guesswork. On a UK Sailmakers mainsail built with a Shelf Foot, the outhaul is what brings the shelf into play: eased, the extra panel along the foot opens like a pocket and adds real depth for reaching and running; hauled tight, it folds flat against the boom and disappears. A flattening reef, a second cringle a short way above the clew, goes a step further and removes the shelf entirely for the heaviest upwind conditions.
Cruising and Racing Perspectives
Cruising sailors tend to set the outhaul once at the start of the season and forget it. That is understandable if the line tails at the mast, but it leaves speed and comfort on the table. Easing the outhaul for a long downwind passage adds power for nothing, and hauling it before a windward beat in a breeze makes the boat stand up.
Racers adjust the outhaul on every leg, sometimes every few minutes as puffs and lulls roll through. Loose-footed mainsails have become the norm in racing precisely because they respond so directly to it, and because a foot without a bolt rope is aerodynamically cleaner. On boats with no backstay adjustment, the outhaul and cunningham are the two quickest ways to change the mainsail’s power without touching the sheet.
Frequently Asked Questions about the Outhaul
Where should the outhaul be set for upwind sailing?
Flat enough that the lower sail shows a smooth, shallow curve with no vertical creases from the clew. In a breeze that usually means the clew pulled nearly to the black band; in light air and chop, ease until the foot has a gentle curve.
Is the outhaul the same as foot tension?
Yes; outhaul, clew outhaul and foot tension all name the same control. On some boats with a fixed clew it is set with a lashing rather than a line, but the function is identical.
The outhaul is a small line that shapes a large part of the mainsail. Use it as actively as you use the sheet and the boat will be easier on the helm in a breeze and livelier in light air, which is exactly what a well-cut mainsail was designed to give you. See also cunningham, vang, foot and clew.