The wireless, solar-powered Wind Instrument RB
set a new standard as the first masthead anemometer with a digital compass inside the wind direction arrow. Traditional masthead anemometers use a potentiometer to measure changes in voltage resistance as the arrow turns with the wind. But those anemometers have to be calibrated to the bow of the boat when installed since they are intended to measure wind angle, and they have a dead zone in the range of 7 degrees where the rotation and voltage resistance starts over.
The Wind Instrument RB does not need to be calibrated; it contains a 9 degree of freedom Inertial Motion Unit (IMU) with a gyro, accelerometer and digital compass. So it knows which way it is pointing even if you just wave it around in the air. But how does it calculate True Wind, and all of the different combinations shown on the menu below?
The raw data measured by the Wind Instrument RB is Apparent Wind Direction and Apparent Wind Speed. It is actually so unusual have a digital compass in a masthead anemometer that the NMEA 0183 format does not include any sentence for Apparent Wind Direction (AWD).
Apparent vs. True: Once we have the measures for Apparent, our software (the SailTimer API) can convert to True wind speed, wind direction and wind angle by accounting for the boat's movement. Apparent is what the wind cups and arrow measure. But when you are sailing along, the boat's movement will cause air flow (the same as if you put your hand out the window of a car while driving). So True Wind accounts for the movement of the boat.