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Course to steer: a worked example

A course to steer is the heading that gets you to your destination despite the tide pushing you sideways. It's one of the core chartwork skills for Yachtmaster, and it's the same triangle every time.

What you need

  • Your start point and destination on the chart.
  • Your expected boat speed through the water.
  • The tidal stream (set and rate) for the time you'll be on passage, from a diamond or atlas. Our tidal stream guide shows how to get it.
  • Variation, your deviation card, and an estimate of leeway if you're sailing.

The one-hour triangle, step by step

You're at A and want to reach a buoy B about 6 miles due east (090°T). Boat speed is 6 knots. The tidal stream for the next hour sets 180°T at 2.0 knots.

  1. Draw the ground track from A to B and beyond. This is the line you want to travel along over the ground.
  2. From A, lay off one hour of tide: 2.0 miles towards 180°T. Call the end of it C.
  3. Open your dividers to one hour of boat speed, 6 miles. With one point on C, swing an arc to cut the ground track. Call where it cuts D.
  4. The line from C to D is your water track: the direction to point the boat through the water. Measure it: about 071°T.
  5. The distance A to D is your speed over the ground: about 5.7 knots, so the 6 miles to B take a little over an hour.

Why it works: in one hour the boat moves 6 miles through the water (C to D) while the water itself moves 2 miles south (A to C). Added together, the boat ends up at D, on the line to B.

Adding leeway

Under sail the wind also pushes the boat sideways. Estimate leeway (say 5°) and steer that much further into the wind. With a northerly wind pushing you south, steer 5° further north: 071 − 5 = 066°T.

Converting to compass

With 2°W variation, 066°T is 068°M. If your deviation card gives 1°W on that heading, the course to give the helm is 069°C. Our variation and deviation guide covers the sign rule.

Passages longer than an hour

Work out roughly how long the passage will take, and get the tidal stream for each hour of it. From A, lay off each hour's tide end to end, so the vectors add up to the total tide over the passage. Then, from the end of the last one, swing an arc of boat speed × the number of hours to cut the ground track. The line from the end of the tide vectors to that cut is the single course to steer for the whole passage.

Don't work out a new course for each hour. Steering a different course every hour to stay exactly on the line means fighting each hour's tide separately, which covers more water and takes longer. One course lets the tides of different hours cancel each other out, and you arrive at B even though you drift off the line along the way.

If the passage isn't a whole number of hours, use the tide for the part hour as a fraction of that hour's vector, and the same fraction of an hour of boat speed.

Course to steer vs estimated position

They're the same triangle used in reverse. An estimated position starts from the course you actually steered and adds the tide to find where you are. A course to steer starts from where you want to go and works back to the heading. If you're asked to check a course to steer, plot an EP from it an hour later: it should land on your ground track.

Common mistakes

  • Swinging the boat speed arc from A instead of from the end of the tide vector.
  • Measuring the course along the ground track (A to D) instead of the water track (C to D).
  • Applying leeway the wrong way: always steer up into the wind.
  • Using the tide for the wrong hour, or mixing UT and BST.
  • Giving the helm a true course instead of converting to compass.

Test yourself, free

Quizzes with every answer explained, and flashcards. No account needed.

Questions

How do you work out a course to steer?

From your start point lay off the tide for one hour, then from its end swing an arc of one hour's boat speed to cut your ground track. The line from the end of the tide vector to that cut is the course to steer.

Which way do you apply leeway?

Steer into the wind by the amount of leeway, so the wind pushes you back onto the water track you want.

Should I work out a new course to steer every hour?

No. For a passage of several hours, lay off all the hours of tide end to end and work out one course for the whole passage. It's shorter than fighting each hour's tide separately.

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Last checked 27 October 2026. DeckPrep is an independent revision tool and is not affiliated with, endorsed by, or operated by the RYA. Always check current requirements with the RYA.