Sail trim: what each control does.

Telltales: the trim gauge

Sailing World places jib luff telltales 10 to 20% back from the luff and leech telltales 15 to 30% down from the head. They are usually green on the starboard side and red on port. It describes three states:

The simple rule, from Practical Sailor drawing on John Rousmaniere's Annapolis Book of Seamanship: if the leeward telltales droop, the sail is trimmed too tight, so ease. If the windward telltales keep lifting, it is eased too far, so trim. Sailing World also says jib leech telltales should flow at least 80% of the time; if the leech stalls, ease the sheet or move the lead aft.

On the mainsail, Rupert Holmes (Sail) says leech telltales should stream horizontally, and if they disappear to leeward the leech is over-tight and stalled. Gary Jobson (Cruising World) gives a matching sign: if the top leech telltale curls behind the sail, the main is too tight.

Mainsheet and twist

Quantum Sails describes the mainsheet as setting boom angle and controlling power and twist. Sheeting harder adds leech tension; easing opens the sail and can reduce heel and weather helm. Quantum's Joel van Wyk calls twist one of the biggest drivers of upwind performance, and Carpenter (US Sailing) says the last few inches of mainsheet trim are the main factor in upwind speed.

Sources use different battens as the upwind twist reference:

• Dave Flynn (Sailing World) sets the top batten parallel to the boom.
• Holmes (Sail) sets the second batten from the top parallel to the boom.

Jobson adds that a top batten hooking to windward means the main is over-trimmed and one falling off to leeward means it is under-trimmed. Holmes recommends more twist for cruisers and short-handed crews because it gives a more forgiving groove, and says headsail twist should generally match the main.

Jibs are touchy. Carpenter notes that a small ease at the clew produces a much bigger ease up at spreader height.

Halyard and cunningham

Quantum says more halyard or cunningham tension pulls the draft forward and flattens the sail; easing lets the draft move aft and adds depth. The cunningham does this without touching the halyard. On the jib, Dieball (North Sails) says more halyard tension rounds the entry and widens the groove, while less gives a finer entry and narrower groove.

Where the draft should sit

The sources differ slightly here:

• Holmes puts the ideal maximum draft 40 to 50% aft of the luff, with typical cruising depth around 15% of the chord.
• Jobson puts maximum draft about halfway aft, and says trimming in moves draft aft (for pointing) while easing moves it forward (for speed).

Outhaul

The outhaul shapes the lower third of the mainsail. Quantum says tighten it to flatten the sail in a breeze and ease it for a fuller, more powerful shape in light air. Holmes notes it flattens the lower sail without moving where the draft sits.

Vang (kicker)

The vang holds the boom down. Quantum says it matters most when the sheet is eased on reaches and runs, because without it the boom lifts and the leech twists open. On boats without a traveler, Holmes says the vang can control twist on its own ("vang sheeting"), and on reaches and runs it becomes the main twist control on every boat. Jobson calls it most useful downwind.

Two cautions from the sources: Quantum warns that over-tensioning the vang strains the mast, boom and gooseneck, and Jobson says not to over-trim it in strong wind.

Traveler

Flynn (Sailing World) splits the work: mainsheet for coarse adjustment (twist), traveler for fine adjustment (boom angle). In light air the car sits well to windward so the boom can be centered while the sheet stays eased. As wind builds, the car moves down. Quantum says lowering the traveler in a breeze depowers without adding excess twist.

Rig type changes how much you use it. Flynn says masthead rigs with overlapping headsails use the traveler a lot, while fractional rigs with large mains keep it near the centerline and play the mainsheet more.

Jib leads

Practical Sailor (after Rousmaniere) recommends three pairs of luff telltales at one quarter, one half and three quarters of the way up. When all three windward telltales lift together as you head up, the lead is right.

• Top lifts first: lead too far aft, leech too open.
• Bottom lifts first: lead too far forward, leech too tight.

For conditions, Practical Sailor moves the lead one or two holes aft in heavy weather to spill wind, and one hole forward in light wind for a fuller sail. It also advises adjusting leads only after a tack, since sheet loads build quickly.

Sources do not agree on the target in a breeze. Practical Sailor treats even breaking as the goal. North Sails' J/80 tuning guide, which is class-specific, says that above 10 knots the head should break slightly before the lower two-thirds. Sailing World says to aim for even breaking when underpowered, and when overpowered to twist the jib and accept the upper inside telltales not flowing.

Backstay

On boats with an adjustable backstay, Quantum says tensioning it bends the mast, flattens the main and reduces forestay sag, which cuts heel and weather helm in a breeze. Using these controls together to depower is covered on reefing and depowering. The sails themselves are covered on sails.