And why is wind data so important? Every sailor must know which way the wind is blowing in order to perform even the simplest maneuvers and calculate routes. Wind can make the difference between a great trip and a terrible one.

The Wind Triangle

Wind direction calculation can be easily explained through the “Wind Triangle”, which shows the relationship between boat speed, Apparent Wind (the wind you feel while sailing), True Wind (the wind relative to the water surface) and compass heading.

True Wind Direction

True Wind Direction is the direction of the wind according to the compass relative to the water. It is measured from the boat, which can be facing any direction and hopefully sailing at a good speed. So, to get an accurate reading, the wind direction must be calculated by multiple sensors and not just one. Simply put: True Wind = Boat Speed ​​+ Apparent Wind.

Angles vs. Directions

An important distinction needs to be made when talking about instruments, and sailing in general: We usually refer to a value relative to the boat as an Angle (for example, the Apparent Wind Angle is 35 degrees starboard of the bow). A value relative to an external point such as water or another point on Earth is a Direction (for example, the True Wind Direction is 315 degrees magnetic).

Unfortunately, it is quite common to see True Wind Direction used to actually refer to True Wind Angle – even by instrument manufacturers who should know better. When using your instruments you should always know the difference between angles and direction.

Advanced wind calculations

Using Heading and True Wind Angle data to calculate True Wind Direction is an accurate enough formula to monitor wind shifts. However, it does not take into account how the boat is sailing through the water.

When you are heeling into the wind, the effect of leeway (when the boat moves sideways through the water) will come into play. If you add the leeway angle to the boat's heading you will get the Course. Advanced instrumentation systems calculate wind using the Course and not the Heading.

Course is the direction you sail through the water. You shouldn't confuse it with the COG, which is the Course Over the Ground.

And that’s all for our tips for this week, but don’t miss the next chapter where we’ll go a little deeper into the topic of “Displaying data.” See you soon.