jungpeter
Guru
Hi All,
I think I'm being confused by semantics here. Can someone explain this information (from the Airmar website) that is thoroughly confusing me:
"Virtually all mechanical and ultrasonic anemometers report apparent wind speed and direction. The Airmar WX Series is unique because it calculates both theoretical and apparent wind speed and direction. These wind readings are the same if the unit is mounted in a fixed location. However, if the WX Series is mounted on a moving vehicle, the apparent wind is the wind you would feel on your hand if you held it out the window while going down the highway. Since the WX Series has a built in GPS and compass, it calculates the theoretical wind based upon the apparent wind, speed of the vehicle, and compass heading. "
So far, so good. As a long-time sailor, I'm intimately familiar with the concept of true (never heard it called "theoretical" wind before!) and apparent wind, and the instrumentation and calculations necessary to determine one from the other. However, later in the same document from Airmar, they state:
"True Wind: True wind is the same as above BUT relative to True (or magnetic) North. In the case of a moving vehicle, True wind is not relevant because the vehicle will (almost) never be aligned to True (or Magnetic) North. In a mobile application True wind is a meaningless value."
Ehhh???? I be confused. True wind (and I believe Airmar's definition of Theoretical Wind) is the absolute direction on the surface of the earth from which the wind originates, and has nothing to do with the alignment and/or the speed of the vehicle (or boat in our case). AND it can be calculated and reported in true bearing, OR magnetic. So what the heck does Airmar mean by "...In a mobile application True wind is a meaningless value."???
Regards,
Pete
I think I'm being confused by semantics here. Can someone explain this information (from the Airmar website) that is thoroughly confusing me:
"Virtually all mechanical and ultrasonic anemometers report apparent wind speed and direction. The Airmar WX Series is unique because it calculates both theoretical and apparent wind speed and direction. These wind readings are the same if the unit is mounted in a fixed location. However, if the WX Series is mounted on a moving vehicle, the apparent wind is the wind you would feel on your hand if you held it out the window while going down the highway. Since the WX Series has a built in GPS and compass, it calculates the theoretical wind based upon the apparent wind, speed of the vehicle, and compass heading. "
So far, so good. As a long-time sailor, I'm intimately familiar with the concept of true (never heard it called "theoretical" wind before!) and apparent wind, and the instrumentation and calculations necessary to determine one from the other. However, later in the same document from Airmar, they state:
"True Wind: True wind is the same as above BUT relative to True (or magnetic) North. In the case of a moving vehicle, True wind is not relevant because the vehicle will (almost) never be aligned to True (or Magnetic) North. In a mobile application True wind is a meaningless value."
Ehhh???? I be confused. True wind (and I believe Airmar's definition of Theoretical Wind) is the absolute direction on the surface of the earth from which the wind originates, and has nothing to do with the alignment and/or the speed of the vehicle (or boat in our case). AND it can be calculated and reported in true bearing, OR magnetic. So what the heck does Airmar mean by "...In a mobile application True wind is a meaningless value."???
Regards,
Pete