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Discover the best angle for sailing into the wind. While it is impossible to sail directly into the wind, it is possible to move upwind by sailing at an angle across the wind. This is called tacking. Construct a simple model sail and test it to see what your minimal tack angle is. Materials
  • small lump of clay
  • protractor
  • pair of scissors
  • transparent tape
  • metric ruler
  • unsharpened pencil
  • clear plastic wrap
  • plastic straw
  • kite string about 30 cm (1') long
  • blow dryer
  1. To construct your sail, cut a piece of plastic wrap into an equilateral triangle whose sides are each 15 cm (6") long. Cut the straw to 14 cm and roll the clay into a ball. Insert the pencil into the clay so that it is standing vertically. This will be your mast. Wrap one side of the triangle around the pencil so that it overlaps about 1 cm and tape it in place. Thread the string through the straw and tie one loose end around the base of the pencil where it sticks into the clay. Hold the straw out from the mast and tape the bottom edge of the plastic wrap to it. The straw will be your boom.
  2. Place your protractor with the zero point directly under the mast and press the clay down to hold it in place. (The boom should line up parallel with the zero line on the protractor.) Place your hair dryer's barrel 30 cm (1') in front of the mast. Turn it on low and aim it directly at the mast. The sail should luff. If the sail and mast blow over, move the dryer farther back.
  3. Slowly pull the loose end of the string out at right angles across the protractor and watch the sail. As soon as the sail begins to fill with air, measure the angle that the boom makes with the zero line on the protractor. Repeat this so you get an accurate reading, and then average your readings.
  4. Place the hair dryer directly behind the sail at the same distance that you had it in front of the mast. Start with your sail out perpendicular to the barrel of the hair dryer and slowly use the string to pull the sail in until it ends up parallel with the wind direction. Watch the sail and mast and feel the tug of the string as you do this. Questions 1. At what angle did the sail first fill with air when you were running into the wind? What does this tell you about the minimum angle at which you can sail into the wind? 2. When you were sailing with the wind, at what angle did the sail appear to have the most power? 3. Can you calculate how far you would have to sail to move directly upwind one kilometer? 4. Why do you get maximum power out of a sail when it is at an acute angle to the wind?


    Additional resources

    1. Newton's Apple Show 1106 (windsurfing).
      GPN: (800) 228-4630. Or call your local PBS station to find out when it will be
    2. 3-2-1 Classroom Contact: Friction: Getting a grip. Videotape. GPN: (800)
      Additional sources of information

      1. Fiberspar
        West Wareham, MA 02576
        (508) 291-2770
        (ice board manufacturer)
      2. U.S. Windsurfing Association
        PO Box 978
        Hood River, OR 97031
        (503) 386-8708