Downwind sailing: angles, trim, gybing and safety

Downwind sailing means sailing with the wind behind you, from a broad reach to a run. Pointing straight at a downwind mark is the shortest route but often not the fastest: angling off onto a broad reach and gybing usually gets you there sooner. The rest is trim, balance and gybing under control.

What is the difference between a broad reach and a run?

On a broad reach the wind comes over the stern quarter, around 135° off the wind. On a run it comes from directly behind, at 180°.

On a run the sails work mostly by drag, like a parachute. On a broad reach they still generate lift, like a wing, so the boat is usually faster. A boat sailing deeper than a broad reach cannot go faster than the true wind.

Why is sailing straight downwind often slower?

Because the boat is slow on a dead run, and the extra speed on a broad reach can more than pay for the extra distance. What counts is downwind VMG: how fast you move away from the wind.

As World Sailing’s coaching material puts it, the straight line is the shortest way, but the further you turn away from it, the faster you go and the further you sail. At 45° off dead downwind you cover about 1.4 times the distance, so you need to go more than 1.4 times faster to come out ahead.

Apparent wind explains the gap. On a dead run your own speed is taken off the wind: in 10 knots of true wind, sailing at 5 knots, you feel about 5 knots. Head up and the apparent wind gets stronger and moves forward.

A worked example from our VMG guide: 9 knots at a 135° true wind angle gives a downwind VMG of 6.36 knots, while 10 knots at 120° gives only 5.00. Most boats find their best downwind VMG around 130° to 150° true wind angle, depending on boat, wind and waves. In light air, North Sails advises against sailing dead downwind: the best course can be as much as 40° above it.

How should you trim the sails downwind?

Ease the sails out as you bear away, then set the kicker and centreboard for the wind strength.

• Mainsheet: let it out until the main just luffs or rests against the rigging.
• Kicker (vang): with the boom out, it controls twist. Keep it snug, and tight in strong wind, which makes a roll to windward less likely. Overpowered on a reach? Easing it spills power.
• Centreboard: as high as the boat allows while it still tracks. On a run it can come nearly all the way up. On a reach, raise it until the boat slides sideways, then lower it a little. If the boat rolls, lower it a few centimetres.
• Jib: without a spinnaker, set it opposite the main on a run (goose-winged), on a pole if you have one.

Where should your weight go, and how much heel?

Move your weight aft as the wind builds. Sitting further back gives the rudder more grip and lifts the bow out of the water.

In very light wind, a slight heel to windward cuts the wetted area. In a breeze, too much windward heel can start a roll that ends in a capsize to windward.

What does sailing by the lee mean, and why is it risky?

You are sailing by the lee when the wind has crossed the centreline and comes slightly from the side the boom is on. At that point the boom can swing across without warning: an accidental gybe.

Watch the top of the mainsail leech: when it goes soft and lifts, the boom is ready to go. Small shifts and rolling in waves can set it off. In a dinghy, an uncontrolled gybe can capsize the boat; on a keelboat, the boom can sweep the cockpit and injure the crew. If in doubt, head up a few degrees, or gybe on purpose.

How do you gybe a dinghy step by step?

Prepare, keep the mainsheet in your hand, and choose the moment the boom crosses.

1. Look around, especially downwind, and check there is room.
2. Set the centreboard partly up. Fully down, the boat can trip over it. A little board down gives more stability through the turn than none.
3. Check the kicker is on enough to stop the boom lifting.
4. Call “Stand by to gybe” and wait for the crew to answer.
5. Bear away smoothly onto a run.
6. Watch the top of the leech. When it goes soft, call “Gybe-ho”, pull the boom across with the mainsheet, keep your head down and move to the new side.
7. As the boom crosses, centre the tiller, or give a little opposite helm, so the boat does not round up.
8. Ease the mainsheet on the new side, cross the jib, reset the board and sail away.

On a keelboat, haul the main to the centreline before the gybe and ease it straight after.

When should you use a spinnaker or gennaker?

Use one when the wind is well aft and you can handle it. A symmetric spinnaker on a pole is best at deep angles. An asymmetric spinnaker or gennaker is a better reaching sail, so boats that carry one sail hotter angles and gybe more. For both, ease the sheet until the luff starts to curl, then trim just enough to take the curl out.

How do you stay safe downwind?

Respect the boom, check the real wind and keep room to leeward.

• The wind feels lighter downwind than it is. Turn back upwind and it will feel much stronger, so check before you run far from your launch spot.
• Keep heads out of the boom’s path whenever the wind is behind you.
• On a keelboat, rig a preventer from the end of the boom to as far forward as possible. Rigged from the middle, it can break the boom. A boom brake slows the boom instead of holding it.
• Racing? Gybe on a lift (the wind moving aft, forcing you up to keep your angle), not on a header.

How can you check downwind VMG and gybe angles with GPS?

Record the session, set the wind direction, and compare downwind legs and gybes. Sail a few minutes deep and a few minutes on a broad reach in the same breeze, and see which gives the better VMG.

Waterspeed counts every tack and gybe and shows how fast and clean each turn was, with the speed you kept through it. Tap a gybe for its entry and exit speed and the angle turned: gybing between two broad reaches at 140° true wind angle is a turn of about 80°. Waterspeed Ultra splits a session into upwind and downwind legs with speed, VMG and angles, and draws a polar chart of your speed at each wind angle. Two limits: VMG uses one average wind direction for the session, and GPS measures speed over ground, so current is in the numbers.

Related: What is VMG?, How to sail into the wind, How to improve your jibes with GPS data, Tacks and gybes.