Tuesday, June 10, 2008

Wind & Points of Sail

Wind Direction

The direction and speed of wind is always graphically displayed on visual weather forecasts. The wind blows along the isobars, keeping low pressure to the left and high pressure to the right. The most reliable way to check wind direction and speed is to consult an anemometer (wind speed indicator).

The first thing you have to understand about the wind is its direction - the wind is named after the direction from which it blows - so a wind blowing from south to north is a south wind. However, the wind direction is only in very rare cases steady (for example the trade winds in the Atlantic are steady) - so you need to be on the alert and always watch what the wind is doing. You should know what to watch, and you'd better don't neglect the signs the wind gives you. For example - waves are created by it, but only the white ripples on the surface show the wind direction. Other boats at anchor or on mooring can give you clues - they float to point into the wind (unless in a case when there is a very strong current). Light and shallow boats prove to be the most reliable indicators. Beware - the sky is a trap! Do not look at it, because the movement of the high clouds have very little to do with the winds that determine what happens where you are. What you can do in advance is prepare the boat with your own indicators: you can adjust a flag or specially made windvane at the top of the mast. The so called the telltales are simple threads - you should put them on the shrouds as high as possible. People who use cloth sails sew very flashy-coloured threads (like magenta, or red) to the sail.

You will become good at that if you practise offboard - always when you are in the open, think about what is going on in the atmosphere around, and particularly what the behaviour of the wind is.

Points of Sail

Points of sail is a term describing different angles from the wind, on which a boat may sail. Depending on where you are going, and where the wind is blowing from, you will choose the direction. Some points of sail are easier to manage than others, and depending on the boat, they will also work differently for you than the others. Therefore, never assume that if someones boat sails fastest when close-hauled, this will be also the case with your boat.

Before we go to the specifics, remember the following:

  • port tack occurs when you have the wind on your port side (left).
  • starboard tack occurs when you have the wind on your starboard side (right).
Close-Hauled - Sailing as close toward the wind as possible without luffing (letting the sails flap); usually boats can sail up to 45 degrees to the wind, although even up to 38 degrees is not unusual.

Close Reach - Any sailing direction between the beam reach, and the close-hauled; the wind is still blowing from ahead (forward of abeam).

Beam Reach -
Sailing at a 90 degree angle from the wind; the wind is blowing from abeam.

Broad Reach - Any sailing direction (heading) between the beam reach and the run; the wind is blowing more from astern (behind).

Run (sometimes called 'Quartering Run", and "Running by the lee") -
Sailing with the wind pushing from astern (behind)

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