B&G Hydra 2000, User Manual

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Hydra 2000 User Manual
Part 3 - Calibration
HB-0844-02
3-18
The idea is to sail on a steady course and drop markers over the
stern at regular intervals, the angle between them and the
centreline of the yacht is measured with a hand-bearing compass
and hence leeway angle is measured. Whilst this is happening the
boat speed and heel angle should be noted at intervals and an
average calculated. These values can then be used to calculate
the leeway coefficient from the following expression:
K = L x Bs x Bs
H
Once the leeway coefficient 'K' is known it is entered into the
system under:
NAVIGATE
→ →
LEEWAY, CALBRATE
→ →
CAL VAL1
3.6 TRUE WIND CORRECTION
It is finally time to go sailing and begin the calibration of the True
Wind Speed and Direction. But before we begin the 'how' a short
discussion of the 'why' is worthwhile.
3.6.1 True Wind Direction Calibration
Why you need to have further calibration for True Wind Direction
will become clear when you go sailing. The true wind might vary in
direction from tack to tack, independently of any wind shifts. This
phenomenon has come to be known as the true wind “tacking”.
This happens because the true wind angle that the instruments are
calculating is wrong.
Fig 3.4 - True Wind Direction