B&G H2000 Pilot *DISCONTINUED* - Manual (Page 70)

HB-0844-04
3-5
3.2 BOAT SPEED/LOG CALIBRATION
3.2.1
Principle of Log Calibration
To calibrate the log it is necessary to work out the number of revolutions of a
paddle-wheel, or sonic pulses per second that correspond to each knot of
Boat Speed. The Boat Speed/Log calibration value is always shown as
Hertz/Knot (Hz/Kt).
The Hydra 2000 allows you to calibrate both a single or a dual sensor unit.
Under normal circumstances with a sensor mounted on the centreline the
single calibration value should be all that is required.
However, if the sensor unit is not installed close to the centreline, or if dual
paddle-wheels are installed, then calibration on each tack will be necessary.
The Hydra 2000 will always use the calibration value for the leeward paddle-
wheel/sensor, using the heel angle if it is fitted or the Apparent Wind Angle if
it is not.
3.2.2
Preparation for Log Calibration
Before calibrating the log you should ensure that the underwater unit is
correctly aligned as follows:
Paddle-wheel - The moulded arrows on top of the unit must be
pointing forward along the fore and aft line of the hull. The unit must
also be totally free of any weed or other fouling.
Sonic Speed - Check that the unit is operating correctly as per the
owner's manual.
3.2.3
Calibration Runs
Consecutive runs, under power, at a constant speed, should be made over a
known distance. To eliminate the effect of tidal conditions, it is advisable to
perform at least two runs, preferably three, along the measured track.
There are three available options for calibrating the log, Automatically (AUTO
CAL), Manually (MANL CAL) or Reference (REF CAL).