Raymarine Ray 106 User's Guide Page 158

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148 RayTech RNS V6.2 - User’s Guide
To read a polar plot:
Refer to the example above and the accompanying definitions:
The bottom axis (1) shows boat speed range in knots. The maximum/
minimum speed and speed interval are determined on the scale
plotted.
The top axis (2) describes an arc of 180
o
representing the boat’s direc-
tion with respect to the wind. At 0
o
you are sailing directly into the
wind, at 180
o
you are sailing directly with the wind.
In this example the lines that lie precisely on the 70
o
and 110
o
axes
correspond to the settings of the Twa1 (3) and Twa2 (4) variables
entered in the polar parameters screen. These lines are displayed in
blue.
The lines that diverge between 30
o
and 50
o
, and 130
o
and 160
o
, repre-
sent the Target Twa upwind (5) and downwind (6). These lines are
displayed in blue.
The line that scribes a semi-circle, plots the optimum heading (7) and
resultant speed relative to the Tws range you enter at the bottom of
the screen. As the Tws range is increased, additional lines are plotted
onto the graph, showing the heading you should take to make
optimum progress as wind speed increases. These lines are displayed
in black.
The co-ordinate pop-up (8) shows the current boat speed and heading,
as entered into the data test screen.
Upwind, downwind and Vmc plot screens
The upwind, downwind and Velocity Made good on Course (Vmc) screens
enable you to directly analyze those aspects of the polar plot by reducing
the displayed information to only those elements.
Upwind plot
The upwind plot screen calculates the best angle and boat speed when
sailing upwind and displays:
Velocity Made Good (VMG) relative to Twa.
Click
Vmg
to view, then select Tws range to plot by clicking on the
Tws (kts))
up/down arrows or entering the numbers direct.
Boat speed relative to Tws.
Click
Bsp
to view.
True wind angle relative to Tws.
Click
Twa
to view.
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D8797_1
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