Sailing downwind is easy to understand: the wind pushes the boat along. Sailing upwind seems almost impossible by comparison. Yet a sailboat can make steady progress toward the direction the wind is coming from, and good upwind sailing is one of the most satisfying skills a sailor can learn.

So how does a boat sail upwind? The answer lies in two wings working together: the sails in the air and the keel in the water. Here is how it works, and how sailors use tacking to reach a destination that lies dead upwind.

The No-Go Zone

No sailboat can sail straight into the wind. There is a range of directions on either side of the wind, called the no-go zone, where the sails simply flap (luff) and stop producing power. Point the boat into this zone and it will slow down and eventually stop.

How close a boat can sail depends on its design and the conditions. Many cruising boats can sail around 40 to 45 degrees off the true wind, while high-performance racing boats can point noticeably higher. Sailing as close to the wind as efficiently possible is called sailing close-hauled. See our guide to points of sail for the full picture.

Sails Work Like Wings

When a boat sails upwind, its sails are not being pushed by the wind like a parachute. They work like an airplane wing turned on its side.

• Air flowing around the curved sail speeds up on the outer, leeward side and creates lower pressure there.
• Air on the inner, windward side is slowed slightly and creates higher pressure.
• The pressure difference produces an aerodynamic force, often called lift, which acts roughly at right angles to the airflow.

When you are close-hauled, that force points mostly sideways, but it also has a forward component. That forward component is what drives the boat upwind. If you sail too close to the wind, the angle between the sail and the airflow becomes too small, the airflow breaks down and the sail luffs. If the sail is sheeted in too tight for the course, the flow separates and the sail stalls. Both reduce drive.

For a broader explanation of these principles, read How Does Sailing Work? The Physics of Sailing.

Apparent Wind

The wind you feel on a moving boat is not the same as the true wind. It is the apparent wind: a combination of the true wind and the wind created by the boat’s own forward motion. When sailing upwind, apparent wind is stronger than the true wind and comes from further forward.

That matters because the sails respond to the apparent wind, not the true wind. Sailors trim their sails to the apparent wind, using telltales on the sails to keep the airflow smooth on both sides. As the boat speeds up or slows down, the apparent wind changes, so trimming upwind is a constant process.

The Keel: The Underwater Wing

The sails alone would push the boat sideways as much as forward. What turns that sideways force into forward progress is the keel (or centerboard on a dinghy).

As the boat moves forward, it slides very slightly sideways, so water meets the keel at a small angle. That makes the keel act as a wing in the water, generating its own lift that pushes back against the sideways force from the sails. When the boat is sailing at a steady speed, the sideways forces from the sails and the keel are in balance. What remains is the forward drive from the sails, which moves the boat ahead. This small sideways slip is called leeway.

Because the sideways force from the sails acts high above the water and the keel’s resistance acts below it, the boat heels. The keel’s ballast and the hull’s shape provide the righting moment that keeps it from going over. Learn more in why sailboats lean and can sailboats tip over.

Dinghies use a centerboard or daggerboard that can be raised or lowered. Upwind it should be fully down to resist leeway; downwind it can be raised to reduce drag.

Tacking: Zigzagging Upwind

Because you cannot sail directly into the wind, you reach an upwind destination by sailing a zigzag course, close-hauled first on one side of the wind and then on the other. Each turn through the wind from one side to the other is called a tack (or coming about).

1. Sail close-hauled: with sails trimmed in, sail as close to the wind as you efficiently can, with the wind coming over one side of the bow.
2. Prepare: check that the way is clear, get the crew ready and call “ready about.”
3. Turn through the wind: call “helm’s a-lee” and steer smoothly into and through the wind. The boat’s momentum carries it through the no-go zone, where the sails produce no drive.
4. Switch the sails: release the jib sheet on the old side and trim in on the new side as the bow passes through the wind. The mainsail swings across by itself.
5. Settle on the new tack: bear away to your new close-hauled course, trim the sails and build speed again.

Good tacks are smooth and quick. Turning too slowly or with too little speed can leave the boat stuck head-to-wind, a situation known as being “in irons.” For more techniques, see our guide to sailing maneuver techniques.

Tips for Better Upwind Sailing

• Steer by the telltales: keep the jib telltales streaming on both sides; if the windward ones lift, bear away slightly, and if the leeward ones stall, head up.
• Don’t pinch: sailing too close to the wind slows the boat and increases leeway. A little lower and faster is often better.
• Control heel: too much heel slows you down. Ease the sheets, flatten the sails or reef when the wind builds.
• Use wind shifts: tack when the wind shifts to head you, so the new tack points you closer to your destination.
• Keep the bottom clean: a fouled hull and keel make a big difference to upwind performance.

How a Boat Sails Upwind: Summary

A sailboat sails upwind because its sails act as wings, producing a force that is partly forward, while the keel acts as an underwater wing that resists the sideways part of that force. The result is forward motion at an angle to the wind. Since no boat can sail directly into the wind, sailors tack back and forth, close-hauled on each side, to work their way upwind. Understanding these forces will help you trim better, steer more accurately and sail faster to windward.