How to Trim the Jib Upwind on a Catamaran
Most people’s relationship with a jib sheet starts and ends with a winch handle — pull it on when you head up, ease it off when you bear away. That gets you moving, but it’s a long way from actually trimming a sail well. Getting real performance out of a headsail upwind means understanding what the leech is doing, how the car controls that, and — more than anything else — what wind angle the sail is actually feeling, which is very often not the number most sailors think it is.
Reading the Leech
The trailing edge of the jib — the leech — tells you most of what you need to know about trim. From where the sheet attaches at the clew, up through roughly two-thirds to three-quarters of the sail’s height, the leech should run about as straight as possible, following the same general line as the mainsail and mast. Above that point, up toward the head, the sail should twist progressively — what’s generally called the twist profile. That controlled twist, rather than a rigid uniform shape top to bottom, is what lets different heights of the sail present an efficient angle to wind that’s itself changing slightly with height.
The Car: Your Primary Twist Control
On a fore-and-aft jib track, car position is the main tool for shaping that twist. Move the car forward and the sheeting angle steepens — more of the sheet’s pull goes into closing the leech down and straightening it, less into tensioning the foot. Move the car aft and the angle flattens, so the foot of the sail (tack to clew) tightens up before the leech does, letting the top of the sail twist open more. Forward for a straighter leech and more power, aft to depower and open the head — that’s the basic lever, and most fine-tuning from there is a matter of small adjustments rather than big swings.
Telltales: The Simplest Read You Have
Telltales remain the most direct, immediate feedback available — no instrument reads airflow better than a piece of yarn actually sitting in it. Windward and leeward telltales should both be streaming, indicating attached flow on both sides of the sail. If the windward telltale lifts, the sail needs to come toward it slightly — either sheet on a touch or head up into the breeze. If the leeward telltale drops or flicks, ease toward it. It’s a simple system, but genuinely worth watching continuously rather than trimming once and leaving it.
What the Draft Stripes Are Actually For
Those bold reference stripes running up a sail aren’t decoration — they exist specifically so you can read the actual curved shape of the sail from luff to leech at each height, not just the overall silhouette. That curve is what generates power: more curve (fuller draft) means more power but a wider entry angle, which pushes your pointing angle away from the wind. Flatter, shallower draft lets you point closer to true wind, at the cost of some power. Balancing that trade-off — full enough to be powerful, flat enough to point — is genuinely one of the harder judgment calls in trim, and it’s exactly the kind of detail worth discussing properly with a sailmaker who can build the shape suited to how your specific boat performs, not a generic template.
Apparent Wind: What the Sail Actually Feels
This is the concept that trips up more sailors than anything else in trim, and it’s worth understanding properly rather than glossing over. A sail never feels true wind — the wind you’d feel standing still. It feels apparent wind: true wind reshaped by the wind your own boat speed generates as it moves. The faster the boat goes, the further forward apparent wind angle moves relative to true wind angle, and the more the two numbers diverge.
A boat sailing at a 45-degree true wind angle might genuinely be seeing an apparent wind angle in the high 20s or low 30s — sometimes even tighter on a very fast boat. America’s Cup catamarans, sailing around the harbour at true wind angles near 45 degrees, can see apparent wind angles as tight as 16 degrees. That gap is exactly why understanding your own boat’s polars matters — not the true wind polars alone, but reverse-engineering them into apparent wind angles, since that’s the actual wind your sails are built to handle and trimmed against. A sail built and trimmed around the wrong assumption of what angle it’ll actually see is a sail that’s never quite right, however carefully everything else is set up.
This distinction matters for autopilot mode too, and the two points of sail genuinely call for different settings. Sailing upwind, steering to true wind angle makes sense — the goal there is holding a consistent angle to the wind that actually exists. Sailing downwind, especially surfing and chasing waves, the sail is responding entirely to apparent wind, so switching the autopilot to apparent wind mode keeps the boat responding to what the sails are actually feeling in the moment, rather than holding a heading that ignores it.
For a deeper look at how apparent wind speed and angle actually diverge from true wind in practice, see Apparent Wind vs. True Wind: The Biggest Misconception in Sailing.
Self-Tacking and Athwartship Jib Tracks
Boats with self-tacking jibs or sideways-running tracks work on a related but distinct logic. The car position here controls angle of attack — how far in or out the sail sits relative to the boat’s centreline — and the golden rule is never bring it all the way to centreline, regardless of how tempting that looks. Racing boats might run five to six degrees of opening at minimum; most cruising setups will sit comfortably in the eight-to-twelve-degree range.
With this kind of track, the jib sheet itself takes over the job of controlling twist, much the way a mainsheet does on a boom. Ease the sheet and it rises first, letting the head of the sail twist open. Sheet on and it pulls the leech tighter and straighter. The car then handles the separate job of moving the whole sail in or out relative to the boat’s centreline. It’s a genuinely different system to a fore-and-aft track, and worth understanding as its own logic rather than assuming it behaves the same way.
Balancing Power and Pointing
Every jib trim decision, ultimately, comes back to the same trade-off: how much twist and power do you want versus how tight and flat do you need the leech to point close to the wind. More twist makes a boat forgiving and easier to sail through sloppy conditions. A tighter, flatter leech with the car pulled aft is the setup for chasing maximum speed in flat water or when you need to depower in a building breeze. Neither is universally correct — it’s a live decision made continuously as conditions change, which is exactly why good headsail trim is treated as a specialist skill on any boat sailed seriously.