B&G Deckman - Manual (Page 101)

Chapter 6: Polars
6.2
certainly the case on Deckman. It is better that the curve is close to the
real performance rather than extremely precise in places but wildly
wrong in others because it is too difficult and slow to adjust, or can only
be adjusted ashore. Moreover, performance curves are a bit of a
moveable feast and super precision is not possible. Deckman does allow
you to get your target speeds and angles right because these are two of
the points which define the curve.
Examples of the polars are available on the B&G website
If you select Polars from the icon bar you will be given the choice of
navigation polar, performance polar or startpolar (as discussed in
Part 1). Remember that the Navigation polar is used for the calculation
of all navigation functions (laylines, leg calculations and so on) and so it
is expected that this will be adjusted on a regular basis; the Performance
polar is used for the calculation of target values so if the helmsman gets
used to a particular set of numbers and doesn’t want them changed this
will not affect accuracy of the navigational calculations.
Deckman has the facility to store different versions of the three different
polars on your computer and then load whichever you choose. There are
a number of advantages of this – for example, you may wish to have
different polars for choppy and flat water, or want to save a version of
your current polars when making amendments to your polar tables. For
more information on this, see ‘Managing polars’ below.
To access the currently loaded polar, select polars followed by
navigation, performance or start polar (see above), then show>loaded.
This will bring up the polar: you will be presented with a table which
shows wind speeds in a column going down the left of the table, and five
pairs of data points going across defined as v1, a1 ... v5, a5; where v1 is
the boat speed at point 1 and a1 is the wind angle. The first point (v1,
a1) specifies the upwind target and so the maximum upwind VMG; the
fourth point (v4, a4) specifies the downwind target and so the maximum
downwind VMG. The second and third points roughly divide the gap
between these two, thus the second point is at a reaching true wind angle
around 50 to 60 degrees, and the third another reaching point around 100
degrees true wind angle. The final fifth point is dead downwind at 180