Lesson 30 of 40 · Module 5 — Planning and pilotage

Leeway

How wind pushes a sailing yacht sideways — and how to allow for it.

Day Skipper15 minVideo · Notes · Interactive · Exercises

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0:00 / 4:11Chapter 1 of 9: What is leeway?

Transcript

Point a sailing yacht in one direction, and she rarely moves through the water in exactly that direction. The wind pushes her sideways as well as forwards, so she slides a little downwind of where her bow is pointing. That sideways slip is called leeway. The leeway angle is the angle between her heading and the path she actually makes through the water.
Two directions matter. Your heading is where the bow points, the course you steer by the compass. Your water track is the path you actually make through the water, and on the chart it is the line with one arrow. Leeway always puts the water track downwind of the heading: wind on the port side pushes you to starboard, and wind on the starboard side pushes you to port.
Leeway is greatest when you are close-hauled, sailing as close to the wind as you can, because so much of the wind’s force is pushing you sideways. On a reach there is less, and running before the wind there is little or none. Strong winds, rough seas, a slow speed, a shallow keel and high topsides all add to it. Motor boats make some leeway too, from the wind on their hull and superstructure.
To estimate leeway, look astern at your wake. The wake trails back along your water track, so the angle between the wake and the boat’s centreline is the leeway angle. Judge it by eye, or take a bearing along the wake and another along the centreline with the hand-bearing compass, and find the difference. Note what your boat makes in different conditions, and experience soon gives you a good estimate.
At fourteen hundred our yacht leaves a fix west of Kerran Head, steering zero zero zero degrees by the compass, which works out at three five five degrees true. She is close-hauled on port tack in a west-north-westerly wind, and the navigator estimates seven degrees of leeway. The wind is on her port side, so it pushes her to starboard: add the leeway, and the water track is zero zero two degrees true. Lay off the water track for the four point six miles she has run, then the tidal stream from its end, and you have the EP.
Seven degrees may not sound much. Ignore it, and after just an hour this EP would be about six cables out. Apply it the wrong way, and the error doubles, to more than a mile. And here the wind is pushing the yacht towards the island, so either mistake would put her closer to danger than her plot shows.
For a course to steer, first work the vector triangle, exactly as in the last lesson. From the Kerran Approach buoy to the South Brennan buoy, it gives a water track of zero nine eight degrees true. The wind, from the south-south-east, is on the starboard side and will push her to port, so steer up into the wind by the six degrees of leeway: one zero four degrees true. Then apply variation and deviation as usual, and the helmsman steers one zero three degrees by the compass.
So which way? Picture the wind pushing the boat downwind of where she points. For an EP, move the water track downwind of the heading: add the leeway when the wind is on the port side, and subtract it when the wind is on the starboard side. For a course to steer, do the opposite, and steer up into the wind. Don’t learn it by rote: a quick sketch of the wind settles it every time.
Three mistakes catch people out. The first is applying leeway the wrong way, which doubles the error instead of removing it. The second is applying it to the tidal stream: leeway belongs to the heading, because it is the boat that the wind pushes sideways through the water. The third is forgetting that when you tack, the wind changes sides, and so does the leeway.

In this lesson you will learn

Explain what leeway is: the angle between heading and water track, caused by the wind
Describe how the point of sail, wind, sea state, speed and the boat affect leeway
Estimate leeway from the wake, by eye or with a hand-bearing compass
Apply leeway in an EP (water track downwind of the heading) and in a course to steer (steer up into the wind)
Avoid the common mistakes: the wrong way, applying it to the stream, and forgetting it after a tack

What leeway is

In Lesson 14 you laid off the course steered as the water track, and in Lesson 29 the vector triangle gave you a water track to steer. Both assumed that the boat moves through the water exactly the way she points. Under sail, she rarely does.

The wind presses on the sails, the rig and the hull. Part of that force drives the boat forwards, but part of it pushes her sideways. The keel resists the sideways push — that is one of its jobs (Lesson 2) — but it can’t cancel it completely. So the boat moves slightly crabwise: forwards, and a little downwind. That sideways slip is leeway, and the angle it makes is the leeway angle (usually just called the leeway, in degrees).

Heading — the direction the bow points: the course you steer by the compass, converted to true for the chart.
Water track — the direction the boat actually moves through the water. On the plot it is the line with one arrow.
Leeway — the angle between the two.

Remember that a wind is named by where it blows from: a westerly blows from the west and pushes you east. (A tidal stream is the other way round: it is named by where it flows to.) With the wind on your port side you are pushed to starboard; with it on your starboard side, to port.

Leeway always moves the water track downwind of the heading.

InteractiveLeeway explorer

Set the heading, the wind and the leeway, and watch the water track and the wake. Switch to “Course to steer” to set the water track you need instead and see which way to steer. Try the four presets first.

Heading (°T)355°T

Wind from (°T)300°T

Leeway (°)7°

The wind, from 300°T (west-north-westerly), is on your port side, 55° off the bow. It pushes you to starboard, downwind of your heading.

EP: lay off the water track to starboard of the heading: 355 + 7 = 362, which is 002°T.

Roughly close-hauled: leeway is usually greatest on this point of sail, especially in strong winds.

Why leeway varies

Leeway depends above all on the point of sail — the angle between the boat’s heading and the wind. Roughly:

Point of sail	Where the wind is	Leeway
Close-hauled	Sailing as close to the wind as the boat will go — for most yachts, roughly 45° to 55° off the bow	Greatest: much of the wind’s force is sideways
Reaching	From about the beam, a little forward of it or well aft of it	Less
Running	From astern	Little or none: the wind pushes you along your heading

On any point of sail, you can expect more leeway with:

A stronger wind — more force on the sails and hull.
A rough sea — waves knock the bow off and shove the boat sideways.
Less speed — a keel grips the water better when the boat is moving well, so leeway grows when she is slow, for example just after a tack.
The boat herself — a shallow keel, or a centreboard or lifting keel partly raised, resists less; high topsides and a tall cabin catch more wind (windage).

Leeway is not only for sailing boats. A motor boat has windage too, and the wind on her hull and superstructure pushes her sideways — usually less than a yacht close-hauled, but enough to notice at slow speed.

Estimating leeway

The wake is your best clue. It trails back along your water track, so the angle between the wake and the boat’s centreline is the leeway. Because the boat is sliding downwind, the wake streams out on the windward side of the centreline.

By eye. Look aft along the centreline and judge the angle to the wake. Some navigators fix a simple scale of degrees to the stern rail to make this easier.
With the hand-bearing compass (Lesson 11). From one spot, take a bearing looking aft along the centreline and another along the wake. The difference is the leeway. Both readings come from the same compass at the same moment, so any error in the compass cancels out.
By experience. Note your estimates in the log (Lesson 15) with the point of sail and the wind, and you soon learn what your boat makes. In slack water, the difference between your true heading and the GPS course over the ground is also a rough check — as long as the compass is right.

Worked example

Reading the wake at 1400

1Close-hauled on port tack, you sight aft from the cockpit. Along the centreline the hand-bearing compass reads 178°M.
2Along the wake it reads 185°M.
3Leeway = 185 − 178 = 7°. The wake is out to port of the centreline, on the windward side, as it should be with the wind on the port side.

About 7° of leeway — the figure used in the example below.

Leeway in an EP

To plot an EP, allow for leeway as soon as you have the true heading, before you draw anything:

Course steered → true heading, with deviation and variation, exactly as in Lesson 14.
Apply the leeway downwind to get the water track: add it with the wind on the port side, subtract it with the wind on the starboard side.
Lay off the water track from the fix for the distance run from the log (one arrow).
Lay off the tidal stream from the end of the water track, as before (three arrows). Its end is the EP.
Join the fix to the EP for the ground track (two arrows), and read off the COG and SOG.

Worked example

The 1500 EP with leeway

1At 1400 a fix west of Kerran Head puts you at 49°44.5'N 004°21.9'W. Log 2318.4. You steer 000°C: 000°C − 2° deviation W = 358°M; 358°M − 3° variation W = 355°T.
2You are close-hauled on port tack in a west-north-westerly wind (from 300°T, 55° off the bow) and estimate 7° of leeway. The wind is on the port side, so it pushes you to starboard: water track 355 + 7 = 362, which is 002°T.
3At 1500 the log reads 2323.0: distance run 4.6 M. Lay off 002°T for 4.6 M from the fix.
4The tidal stream sets 070°T at 1.2 kn: in an hour, 1.2 M. Lay it off from the end of the water track and mark the EP.
5The ground track measures 5.2 M on 014°T: COG 014°T, SOG about 5.2 kn.

1500 EP: 49°49.5'N 004°19.9'W

The 1400–1500 example. Dashed: the heading, 355°T. One arrow: the water track, 002°T, 7° downwind of it. Three arrows: the tidal stream. Two arrows: the ground track to the 1500 EP.

In Lesson 14 there was no leeway, so the water track was simply the course steered and its end was the DR. A DR uses the course steered and distance run alone, so with leeway the end of the water track isn’t a DR, and there is no need to mark it: draw the water track and carry straight on with the tidal stream to the EP.

InteractiveEP with leeway

Work out the water track, lay it off with the dividers for the distance run, then add the tidal stream. Each step is checked (within 0.2 M). At the end, compare your EP with one that ignores the leeway or applies it the wrong way. Then try as many new problems as you like.

1400 fix:: ⊙ on the chart, 49°44.5'N 004°21.9'W
Heading:: 000°C → 355°T (000°C − 2° deviation W = 358°M; 358°M − 3° variation W = 355°T)
Wind:: from 300°T (west-north-westerly), leeway 7°
Log:: 1400 2318.4 · 1500 2323.0
Tidal stream 1400–1500:: sets 070°T, rate 1.2 kn

Step 1 of 3: the water track

The dashed line is the heading. Which water track do you lay off?

Leeway in a course to steer

A course to steer works the other way round. The vector triangle (Lesson 29) gives the water track you must make good. The wind will push you downwind of whatever you steer, so you aim off up into the wind by the leeway angle. Then convert to compass as usual. The order is:

Vector triangle → water track (°T).
Leeway: steer up into the wind → heading (°T). Wind on the starboard side: add. Wind on the port side: subtract.
Variation → magnetic (°M).
Deviation, read from the card for the heading you will steer → compass (°C).

Apply leeway before deviation: deviation depends on the way the boat actually points (the ship’s head, Lesson 10), and with leeway that is the heading, not the water track.

Worked example

Kerran Approach buoy to the South Brennan buoy

1The ground track is 093°T, 3.8 M. At 5 kn, with the stream setting 070°T at 1.2 kn, the vector triangle gives a water track of 098°T.
2The wind is south-south-easterly (from 150°T), on the starboard side, and you expect 6° of leeway. It will push you to port, so steer up to starboard: 098 + 6 = 104°T.
3Variation 3°W, added going from true to magnetic: 104 + 3 = 107°M.
4Deviation: 107° is between 090° (4°E) and 135° (5°E). The card changes by +1° over those 45°, and 107° is 17° along: +1 × 17/45 = +0.4°. Deviation = +4 + 0.4 = +4.4°, or 4°E to the nearest degree. Easterly deviation is subtracted going to compass: 107 − 4 = 103°C (check: the card at 103°C gives 4°E too).

Steer 103°C

Steering 104°T, 6° up into a south-south-easterly wind, the leeway carries the yacht along the water track of 098°T that the vector triangle asked for.

Which way? A summary

	Wind on the port side	Wind on the starboard side
EP: water track	Heading + leeway	Heading − leeway
Course to steer: heading	Water track − leeway	Water track + leeway

An EP goes downwind of the heading. A course to steer aims up into the wind.

InteractiveWhich way?

Each question gives a heading or a water track, the wind and the leeway. Pick the answer, then check the explanation and the picture. Keep going until it is automatic.

Working an EP

You have been steering 335°T. The wind is from 025°T and you estimate 5° of leeway. Which water track do you lay off?

Score: 0 of 0

Common mistakes

Applying it the wrong way. This doesn’t just fail to correct the error — it doubles it. In the 1400 example, ignoring the 7° of leeway puts the EP 0.6 M out after an hour; applying it the wrong way (water track 348°T) puts it 1.1 M out.
Applying it to the tidal stream (or to the ground track). Leeway is the boat being pushed through the water, so it belongs to the heading. The stream is laid off with its own set and rate, unchanged.
Forgetting it after a tack. When you tack, the wind moves to the other side, and so does the leeway. In the example, after tacking onto starboard tack she would head about 245°T, and the water track would be 245 − 7 = 238°T — subtract, not add. End the EP’s first leg at the time of the tack and start the new water track from there.
Mixing up the wind’s direction. The wind is named by where it comes from. A wind from 300°T pushes you towards 120°T.

Check your understanding: on starboard tack you steer 245°T with the wind from 300°T and 7° of leeway. What water track do you lay off for your EP?

Key terms

Leeway: The sideways slip of a boat caused by the wind, measured as the angle between heading and water track.
Heading: The direction the bow points; the course steered, converted to °T for the chart.
Water track: The direction the boat actually moves through the water: heading allowing for leeway. One arrow.
Close-hauled: Sailing as close to the wind as the boat will go — roughly 45° to 55° off it. Usually the most leeway.
Reaching: Sailing with the wind roughly on the beam. Usually less leeway.
Running: Sailing with the wind from astern. Little or no leeway.
Windage: The parts of a boat above the water that catch the wind: hull, cabin, rig.
Wake: The disturbed water left astern; it trails along the water track.
Steering up into the wind: Aiming upwind of the water track by the leeway angle, so the leeway carries you onto it.
Port / starboard tack: Sailing with the wind on the port / starboard side. The leeway changes sides when you tack.

Exercises

Check your understanding. You get a second try at each question, then the worked answer. Score 70% or more to complete the lesson — your progress is saved in this browser.

What is leeway?

You are steering 090°T with the wind from due north (000°T). Which way does leeway move your water track?

You have been steering 220°T. The wind is from 280°T and you estimate 5° of leeway. What water track do you lay off for your EP?

Your vector triangle gives a water track of 310°T. The wind is from 255°T and you expect 6° of leeway. What true heading should you steer?

The vector triangle gives a water track of 198°T. The wind is from 270°T and you expect 4° of leeway. Variation is 3°W. The deviation card (Lesson 10) gives 180°C 3°E, 225°C 0°. What compass course do you give the helmsman?

Close-hauled, you sight aft with the hand-bearing compass. Along the boat’s centreline it reads 300°M; along the wake it reads 295°M. How many degrees of leeway are you making?

On port tack you have been adding 6° of leeway to your heading to get the water track for your EP. You tack onto starboard tack. What do you do now?

Where does leeway go when you plot an EP?

When would you normally expect the most leeway?

At 0915 you pass close to No 1 buoy and take that as your fix. You steer 135°T with the wind from 185°T and estimate 5° of leeway. The log reads 1532.6 at 0915 and 1536.4 at 1000. The tidal stream for the period sets 235°T at 1.5 kn. Plot your 1000 EP: lay off the vectors on the plotting sheet, then tap the same spot on the second chart.

Plotting sheet: A starts on the 0915 fix. Move B until the readout shows the water track and the distance run, then pencil it in. The dividers then start from the end of your water track, ready for the tidal stream.

Distance A→B: 0.60 MBearing A→B: 225°TDrag A and B, or Tab to them and use the arrow keysZoom with + / −, drag to pan

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Leeway drill

Five fresh questions each time: a water track for an EP, a heading (or compass course) to steer, which side the wind is on or a wake reading, a quick concept check and an EP with leeway to plot.