Understanding Polar Diagrams

Posted by: “C Spear” spear.c@comcast.net freespearitsailboat

Polar diagrams show the boat speed at various points of sail. Let’s look at the innermost curve (labeled 6.0) as an example.

Polar_Diagram_387 Wing Keel, 150 Genoa

1. First delete all the other curves in your mind so you are looking at only one curve
2. Now look at the two scales
a. The horizontal scale goes from 1 knot to 9 knots – it represents boat speed
b. The vertical scale at the bottom represents wind speed from 6.0 to 20 knots
c. The numbers on the outside of the half-circle represent the angle you are sailing relative to the true wind direction – straight up (0 degrees) is directly into the wind and straight down (180 degrees) is dead down wind
3. Back to the inner curve the true wind speed is 6.0 knots (not apparent wind speed)
4. Following that inner

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