Wind speed and direction never stay the same – they are constantly changing. While these changes are often small and subtle, they can be substantial. You will, with experience, develop a skill called wind sensing or wind feel which helps you detect the wind and anticipate its changes.
How can you tell the direction of the wind? The easiest way is to simply use your rig like a weather vane. Hold the rig upright and let it pivot freely. The front edge (luff) of the sail will point toward the wind (upwind) and the back edge will point away from the wind (downwind).
Other visual wind indicators are flags, smoke, and trees. Sometimes clouds can be used, since they often move in the same direction as surface wind.
As you become more experienced, you will also sense wind direction and speed by feeling the wind on your face and neck, and looking at the ripples or waves on the water. Ripples and waves are usually perpendicular to the wind.
Before your first sail, your instructor will show you how to determine wind direction and speed. By knowing where the wind is coming from, you will know the best way to prepare and carry the rig, launch, sail, and return to shore again.
Puffs, Lulls, True Wind and Apparent Wind
Sudden changes in wind speed are called puffs or lulls. A puff is an increase in speed for a short duration, and a lull is a decrease in speed, sometimes called a “hole” in the wind. It is a rare day when the wind is truly steady. Most of the time, you will sail in and out of many puffs and lulls.
You can see and feel puffs and lulls. A puff usually makes the water surface look darker. A lull is a bit more difficult to see – usually lighter in color and smoother than the surrounding water. Get in the habit of always watching the water for puffs and lulls.
Reading puffs on the water
In describing the speed or strength of the wind, the nautical term knots is frequently used. One knot is about 20% more than one-nautical-mile per-hour (1 knot = 1.2 mph, or 10 knots = 12 mph).
When first learning to sail you may be confused by how the wind speed seems to almost disappear when you sail downwind (wind coming from behind the board) and increase again when you sail upwind (wind coming from ahead). To understand why this happens, you need to know the difference between true wind and apparent wind.
True wind is exactly that – the speed and direction of the wind that you feel when you are not moving. Apparent wind is a combination of the true wind and the wind created by your own motion. When you stick your hand out the window of a moving car, what you feel is apparent wind – wind created by the motion of the car in combination with the true wind that is blowing. The same phenomenon occurs – to a lesser extent – when your board moves. The faster your board is moving, the more apparent wind you create.