They are not too difficult to create, but it does take time.
Simply take many data points and plot with Excel as a circle plot.
Sail Delmarva: Speed Polars
You have to play some games with interpolation and smothing, since wave conditions and load will vary over time. In someways the targets of others are better (depending on how they were developed) and in some ways your own are more valid.
I found I mostly worked on this during long, dull watches.
(when asked how he reached the starting holds on a difficult rock climbing problem that clearly favored taller climbers - he was perhaps 5'5")
"Well, I just climb up to them."
by Joe Brown, English rock climber
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