B&G Hydra 2000, User Manual

Page: 55 / 147

Hydra 2000 User Manual
Part 2 - Operating Information
HB-0844-02
2- 39
2.11.39 True Wind Speed
Menu Heading: WIND
Function Text: TRUE W/S
Update Rate: Once per second
Units: Knots, metres per second
Notes
1. Corrected for masthead and other errors via a Look-Up Table
(see Part 3 - Calibration).
2. Variable damping 0-99 seconds.
True wind speed is required by the Trimmers for decisions on
sails, and to check their trim as the wind changes.
When the boat is sailing downwind, the air passing over the mast
is accelerated and tends to make the true wind speed over-read
downwind. The Hydra has a calibration to correct for this which is
explained in
Part 3 - Calibration.
2.11.40 Velocity Made Good (VMG)
Menu Heading: SPEED
Function Text: VMG
Update Rate: Once per second
Units: Knots
Note
Upwind and Downwind.
Velocity Made Good (VMG) is calculated from the true wind angle
and the Boat Speed as shown in Fig 2.5. VMG is a measure of
your performance upwind and downwind and is more important
than Boat Speed, since it takes into account how close you are
sailing to the wind. However, it is not possible for the helmsman to
sail to it directly because of the momentum of the boat.
As you sail closer to the wind the VMG will initially rise, because
the boat will hold its speed due to its momentum. So VMG
increases and the helmsman, seeing this, would be encouraged
to sail even higher to increase the VMG even more. Of course if
you carry on like this you will eventually end up head to wind, the
boat will stop dead and the VMG will plummet.