Polar curves represent the boat speed for a given wind speed and angle : SOG = fpolar(TWS, TWA).
SailGrib WR uses the same polar format as Maxsea or Adrena. A polar file is a tab delimited text file where each line represents the boat speeds for a given true wind angle and each column represents a wind speed.
To avoid problems, the boat speeds can be formatted with “.” or “,” as decimal separators.
It is better if a polar file has a line for 0° and 180° and columns start with a wind speed of 0 knot.
Here are the rules if SailGrib does not have a value for a particular wind speed and angle:
- If the wind speed is greater than the highest wind speed value in the polar file, SailGrib WR will take the value corresponding to that highest wind speed.
- If the wind speed is lower than the lowest wind speed value in the polar file, SailGrib WR will interpolate between 0 and the value corresponding to that lowest wind speed.
- If the wind angle is higher than the highest wind angle value in the polar file, SailGrib WR will use the value corresponding to that highest wind angle.
- If the wind angle is lower than the lowest wind angle value in the polar file, SailGrib WR will use a 0 value for the boat speed.
It is highly recommended to include high wind speeds in the polar file and to have low boat speeds for these high wind speeds.
Just for illustration, a simple example of a polar lacking the high wind speed values would be:
SailGrib WR comes with a set of polar files that we have compiled from different sources like boat builders, naval architects or ORC certificates. They should be considered as a starting point for your specific boat and you should adjust them accordingly.
All of them are under the same format with boat speed values for TWA (true wind angle) equals to 0°, 5°, 10°, 15°, 20°, 25°, 32°, 36°, 40°, 45°, 52°, 60°, 70°, 80°, 90°, 100°, 110°, 120°, 130°, 140°, 150°, 160°, 170° and 180° and TWS (true wind speed) values for 0, 4, 6, 8, 10, 12, 14, 16, 20, 25, 30, 35, 40, 45, 50, 55 and 60 knots.
We keep adding polars to the app: more than 400 polars are already in our database.