B&G H2000 Pilot *DISCONTINUED* - Manual (Page 75)

HB-0844-04
3-10
(13) Press Enter, the current boat speed will be converted to and
displayed in the newly selected units.
3.3 APPARENT WIND SPEED/ANGLE CALIBRATION
3.3.1
Principles of Wind Speed/Angle Calibration
Wind shear and wind gradient can be a problem when calibrating apparent
Wind Speed and Angle. It is easy to see how shear can affect the Apparent
Wind Angle; no sooner have you set it up than the shear changes and
everything is out again. This can lead to a circular situation if you are not
careful. The best solution is to do your calibration on a day when the shear is
minimal and thereafter leave it as an indicator of the Wind Angle at the
masthead, always remembering that this is not necessarily the wind angle
that you are sailing at.
How do you know the shear is minimal? If you are finding it easier to attain
speed on one tack than the other, then there is shear. A good look at the
general weather conditions is also helpful. Do not calibrate in building sea
breezes!
What of wind gradient then? Well, this is the biggest culprit for getting true
wind speeds accused of gross inaccuracy. The problem is that most people
use the wind speed as a measure of the pressure or force of the wind, which
it is not. It is a measure of the wind speed at the top of the mast, and that is
all. If it is 12kts at the top of the mast and only 4kts at the water, then the
breeze will feel a lot softer and provide less power for the rig than if the
breeze is twelve knots all the way down to the water.
This is why we recommend that the last thing you touch is the Apparent Wind
Speed. It is calibrated in the factory where wind tunnel calibrated units are
available, and apparent inaccuracies are more likely attributable to effects
such as wind gradient, rather than to a basic calibration problem.