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has stored the geographical coordinates of the two reference points and assumes that the wind direction is
the same as the heading from the downwind point to the upwind point. These points only serve to tell the
device the wind direction. They could be anywhere; on the beach, in the parking lot or on the water. The
only thing that matters is that one point at least 75m or more directly upwind of the other.
It is possible to set the reference points in the opposite order, i.e. upwind first, then downwind. Also, the
reference points can be reset independently. That is to say you could change the upwind reference point
while keeping the same downwind point.
Reference points are stored in non-volatile memory so they are not lost when the device is switched off. If
you often sail somewhere where there is a consistent seabreeze you don’t need to program in a new wind
direction every time you train with the S5.
3.
After you have stored the locations of the two reference points, the S5 will indicate both your upwind and
downwind VMG in real time. This will always be a positive number. When you are pointing higher than a
beam reach this will be your VMG upwind, if you are sailing lower than a beam reach it will be your VMG
downwind. If you sail on a beam reach the device will display a very small number no matter how fast you
are going.
Tip for Windsurfers:
Twist the S5 around your boom so that it faces your sail before you tack. You will then be able to read the display
(now upside down) through your sail window on the new tack.
Frequently Asked Questions
What is VMG?
A good way to understand Velocity Made Good (VMG) is
to imagine a power boat and a windsurfer traveling from a
leeward (downwind) mark to a windward (upwind) mark
together. The powerboat travels along a straight line
between the marks while the sailor tacks back and forth to
get upwind.
Now imagine that the driver of the powerboat controls the
powerboat’s speed to keep the windsurfer directly abeam
of the powerboat and not ahead of or behind it. The speed
that the powerboat must travel to keep even with the
windsurfer is the windsurfer’s VMG.
As shown in the diagram, the actual speed of the
windsurfer can be broken up into two perpendicular
components: useful speed (VMG) and wasted speed that
does not help the windsurfer get upwind.
All this also applies to a windsurfer jibing back and forth
to get downwind. In this case VMG represents how fast
the windsurfer is getting downwind.
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