If you've experienced sailing for a while, you know that the wind can be unpredictable. It's inescapably central to the experience, but learning how to take advantage of it can be very frustrating, and to further complicate matters, there are two different types of wind, true wind, and apparent wind. In this article, we’ll be discussing what is apparent wind and the difference between apparent and true wind.

What Is Apparent Wind?
Apparent wind is the wind that we feel and experience when we are in motion. It's a combination of the actual wind (the real wind) that blows over land and sea, and the wind we make as we move forward.

Apparent wind angle
Apparent wind speed also changes with your heading relative to the wind direction. The faster you move, the greater the apparent wind angle change. In short, the faster you go, the closer the apparent wind angle will be to your front.

Where Is Apparent Wind Used?
During sailing, especially at high speeds, apparent wind is a key factor determining whether a sailboat can sail effectively. A vessel traveling at an increased speed relative to the prevailing wind will encounter a reduced angle and increased speed of the wind driving the sails. Ultimately, the increased drag and reduced efficiency of the sail at very low angles will result in a loss of acceleration force.

Windsurfers and certain types of boats are able to travel faster than true wind. Ice sailors and land sailors also usually fall into this category because they have relatively little drag or friction. In fixed-wing aircraft, the apparent wind is what is experienced onboard and determines the speed required for takeoff and landing. Aircraft carriers usually sail directly against the wind at maximum speed to increase the apparent wind and reduce the necessary takeoff speed. For the same reason, overland airport traffic and most medium and large birds generally face upwind during takeoff and landing.

How Is Apparent Wind Measured?
Apparent wind is often quoted as the speed measured by a masthead sensor that contains an anemometer and a vane that measures wind speed in knots and wind direction in degrees relative to the ship's heading. Modern instruments can calculate true wind speed when entered with apparent wind and boat speed and direction.

Difference Between True Wind And Apparent Wind
True wind speed is the actual wind speed measured by a stationary object. Apparent wind speed is the speed of wind perceived by an object moving through the air, such as a boat or yourself. In other words, the apparent wind speed combines the actual wind speed and the effective wind speed produced by the motion.

The oncoming wind and the wind adjusting the sail while in motion are the obvious winds. It is a combination of true wind speed and direction and boat speed and heading. When you are sailing close, the true wind may be at a 45-degree angle to your windward bow. But your forward motion causes the apparent wind to blow from a slightly forward direction and faster than the true wind.

Apparent wind is important as it helps predict how much power the wind will produce. Apparent wind differs in speed and direction from the true wind experienced by a stationary observer and consists of true wind speed (TWS) and true wind direction (TWD). Modern instruments can quickly measure apparent wind speed and perform simple calculations based on boat speed and direction to immediately tell us the true apparent wind speed in milliseconds. However, it is very important to ensure that your instruments are regularly calibrated and checked, otherwise, the information you receive will be of no use.

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