Sail controls

Acts on: Hauls the boom down and inboard through a multi-part tackle, shortening the distance from the sail's head to its clew and tensioning the leech.

Effect: Two modes. Close-hauled, the sheet pulls mostly downward: trimming closes the leech and removes twist, easing lets the top of the sail fall open. Once the boom is eased out, the pull turns mostly horizontal, so the sheet stops controlling the leech and simply sets the sail's angle to the wind — the vang takes over the twist.

Use it: Upwind, use the sheet to set twist: top batten roughly parallel to the boom, top leech telltale flowing most of the time with an occasional stall, then make angle changes with the traveler rather than re-trimming. On a reach, play the oldest game in sailing — ease until the luff just bubbles, trim until it stops. Over-trimming is the most common error afloat.

Acts on: Slides the mainsheet's attachment point sideways along a track across the boat, carrying the whole boom to windward or leeward.

Effect: Changes the mainsail's angle of attack while sheet tension — and therefore twist — stays essentially the same. That separation is the whole point: power changes, the leech does not. (It is a first-order model: strictly exact only while the sheet still pulls near-vertically, but it is the right way to think about it.)

Use it: Set the twist with the mainsheet, then position the boom with the traveler: car up toward — even above — the centerline in light air to center the boom without strangling the upper leech, and dropped down in puffs to shed power without wrecking the trim. In big, fast puffs, a quick mainsheet ease dumps power faster than the traveler can.

Acts on: Pulls the boom down toward the mast step from a point partway along its length, tensioning the mainsail's leech independently of the mainsheet.

Effect: Off the wind it is the twist control: with the sheet eased the boom wants to rise and the top of the sail to fall open, and the vang is what stops it. Upwind it adds leech tension on dinghies and in a breeze; on a cruising keelboat upwind in light-to-moderate air it usually just sits snug while the mainsheet does the leech work.

Use it: Set it on a reach or run so the top batten lies roughly parallel to the boom. Vang sheeting — cranking the vang until it owns the leech, then playing the mainsheet purely for angle of attack — is standard on dinghies and on any boat without an effective traveler. Ease it before rounding up in a blow, or the pinned leech will fight you.

Acts on: Pulls the mainsail's clew aft along the boom, tensioning the foot of the sail.

Effect: Foot tension shows up mostly in the lower third of the sail: haul the outhaul tight and the lower sail flattens and depowers; ease it and the foot rounds into a deeper, more powerful curve.

Use it: Tight for beating, for a building breeze, and for flat water where a flat, close-winded sail pays; eased for light air, reaching, and chop where you need power to punch through. It is one of the cheapest controls to adjust — re-set it whenever the wind or your course changes meaningfully.

Acts on: Hauls down on a reinforced eye a short way up the mainsail's luff, tensioning the luff below the halyard's lock-off.

Effect: Exactly what extra halyard would do: luff tension pulls the draft forward and flattens the sail's entry. As the breeze builds and blows the draft aft, the cunningham brings it back — a typical mainsail target is draft about 45–50% aft of the luff, though the number is a guide, not a spec.

Use it: Reach for it when the sail is under load and the halyard will no longer shift: tension in a building breeze until the luff wrinkles just disappear, and leave it slack in light air, where a soft luff and a few wrinkles are correct. Racers value it for a second reason — the halyard may already be at full hoist with nowhere left to go.

Acts on: Tensions the stay running from the top of the mast to the stern, compressing and bending the mast and loading the forestay.

Effect: Rig-dependent, and worth learning both ways. On a fractional rig the dominant effect is mast bend, mostly in the upper half to third of the spar: bend pulls cloth toward the luff and leech, flattening the mainsail and opening its upper leech. On a masthead rig the dominant effect is forestay tension: less sag to leeward, so the genoa flies flatter with a finer entry and the boat points higher.

Use it: Wind it on as the breeze builds to depower — flatter main, firmer forestay — and ease it right off in light air so the sag powers the genoa up with a deeper, rounder entry. Boat-dependent caveat: swept-spreader fractional rigs take much of their forestay tension from the shrouds, so how the effects split varies from boat to boat.

Acts on: Pulls the headsail's clew aft and inboard toward its fairlead car; only the leeward (working) sheet is loaded at a time, the windward one lying lazy.

Effect: In and out sets the headsail's angle of attack. Close-hauled it also closes or opens the leech, because the sheet loads both foot and leech through the clew.

Use it: Off the wind, the reaching rule: ease until the luff just breaks, trim until it stops — when in doubt, let it out. Upwind, steer and trim to the luff telltales: a fluttering windward telltale means sheet in or bear away; a fluttering leeward telltale means ease or head up; both streaming aft means the flow is attached and the sail is working.

Acts on: Moves the sheet's turning point fore and aft along a deck track, changing the angle at which the sheet pulls on the clew.

Effect: Car aft: the sheet pulls more along the foot, so the foot flattens while the upper leech opens and twist increases — the depowering setup. Car forward: the sheet pulls down harder, closing the leech, reducing twist, and deepening the foot — power for light air and chop.

Use it: Check the lead by steering slowly toward the wind: the windward telltales should break evenly from top to bottom. Top breaks first — the car is too far aft, move it forward; bottom first — move it aft. A good starting point puts the sheet's extended line through the middle of the luff, and move the car forward as you part-furl a genoa. A barber hauler, where fitted, does the same job athwartships — inboard for pointing, outboard for reaching.

Acts on: Rotates the drum at the base of the forestay foil, winding the sail around the stay as the line is hauled and letting it unwind as the sheet pulls the sail out.

Effect: Counter-intuitive but important: partially furling a genoa makes it fuller, not flatter. Rolling the sail concentrates its built-in camber, so a part-furled genoa sets baggy and draft-aft exactly when you want it flat. Foam or rope luff pads are built into some sails specifically to soak up that extra cloth mid-luff.

Use it: Furl and unfurl with light tension on the working sheet so the sail rolls up tight, and move the fairlead car forward as you furl — the clew moves forward and up. Treat a part-furled genoa as a compromise reef: it works, but if you sail reduced often, a foam-luff sail or a smaller headsail sets far better.

Acts on: Hoists the sail and, once cleated or locked off, sets the base tension along the sail's luff.

Effect: More luff tension pulls the draft — the deepest point of the sail's curve — forward and flattens the entry; less tension lets the draft drift aft. As the wind builds it blows the draft aft, so more halyard brings it back where it belongs.

Use it: Read the luff: in light air a few small horizontal wrinkles along it are correct, so keep the halyard deliberately soft. As the breeze builds, tension until only the lowest wrinkles remain, and in heavy air until the luff is nearly smooth — typical guidance, not an exact law. Once the sail is loaded, adding tension gets hard: that is what the cunningham is for.

Acts on: The topping lift carries the boom's weight from the masthead when the sail is not doing so; lazy jacks form a cradle of light lines that guides the falling sail onto the boom.

Effect: By design, none on sail shape — and that is the trap: a topping lift left tight while sailing lifts the boom and distorts the leech, so once the sail is drawing it must hang slack. Lazy jacks likewise only guide cloth; they are never the boom's support.

Use it: Take up the topping lift before lowering or reefing so the boom cannot drop into the cockpit, and ease it again once the halyard is back on. Slacken the lazy jacks — or point close to head to wind — when hoisting, so the battens do not snag in them. A rigid vang or gas strut holds the boom up by itself and makes the topping lift redundant.