Raymarine Marine GPS System manual RayTech Navigator User’s Guide

RayTech Navigator User’s Guide

To read a Polar plot, refer to the example in Figure 5-18 and the following plot component definitions:

∙The bottom axis shows boat speed range in knots, with the minimum/maximum speed and speed interval determined by you, depending on the scale you want plotted.

∙The top axis describes an arc of 180° representing your boat’s direction with respect to the wind. At 0° you are sailing directly into the wind, at 180° you are sailing directly with the wind.

∙The lines that lie precisely on the 70° and 110° axes (in this example) correspond to the settings of the Twa1 and Twa2 variables found within the Polar Parameters screen. These lines are displayed in blue on the screen.

∙The lines that diverge between 30° and 50°, and 130° and 160°, represent the correlation between True Wind Angle (Twa) upwind and downwind (respectively) and boat speed.

These lines are also displayed in blue on the screen.

∙The line that describes a semi-circle (beginning from 0°, 0 Kts on the example plot) plots the optimum heading and resultant speed relative to the True Wind Speed (Tws) range you enter at the bottom of the screen (see Figure 5-18). As you increase the Tws range, 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 dot and coordinate-pop-up show the current boat speed and heading, as entered into the Data Test screen. The dot is displayed in red, and will only appear if the value entered can be plotted on the current graph.

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