"wind text" polars where are they from?

[briar]

Where does the "wind texts" (best VMC/course) get calculated from? When I use the ruler function i'm getting the correct speed for the wind strength from the loaded polars file but the display in the wind grid doesn't show the correct speed for the suggested angle


Thanks

[omar]

Best VMC/best course are calculated using the
wind rectangle center and the selected destination.
The best course is the one that gives the
larger VMC to the destination.

[briar]

Omar
Thanks but how is the speed calculated if i use the ruler tool it will tell me a speed that matches the polars from th 2011_pro-full.csv file which matches the actual speed from the game but the speed on the wind rectangle is lower

[briar]

Re: "wind text" polars where are they from?
to clarify
Omar
Thanks but how is the "boat speed calculated" if i use the ruler tool it will tell me a "boat speed" that matches the polars from th 2011_pro-full.csv file which matches the actual "boat speed" from the game but the "boat speed" in the wind rectangle is lower

briar

Posts: 3
Joined: Fri Oct 02, 2009 8:57 pm

[omar]

The speed displayed when you activate wind text "best VMC/Course"
is the VMC, not the boat speed.

VMC (Velocity Made good to Course) is the projection
of the boat speed vector in the direction of the destination.
Frequently one cannot point directly to the destination
(wind may be blowing against). VMC is the "usable"
component of the boat speed.

Formula:
VMC = Boatspeed * cos(alpha)
where alpha is the angle between Course and Destination direction.
( destination direction uses great circle calculation )

The program calculates the VMC for all possible courses
and displays the larger value (best VMC)

[omar]

Note that the best VMC shown is in the
center of the wind rectangle (full degree position),
not the position of the boat.
If close to the destination, the best course for the boat
may differ from the one in the center of the rectangle.