Home Page Forums Bluewater Racing General Polar Data clarification

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      Each route has an option named “Boat Type (polar)”. This is a simple string, like “J120”, that tells the program which polar data to use for sailing time calculations. If the boat type is J120, then the program looks for the polar data in a file named “J120.pol” or “J120.txt”.

      When a route is first created, either through the graphical editor, or by importing it from GPS or some other source, the “Default Polar File” entry of the Preferences is copied into the Boat Type option. In other words, the new route is initialized to have the default boat type. After that, you can view or change the boat type by opening the route options window and typing in a new one. This is the only way to change the boat type.

      Changing the “Default Polar File” name in the Preferences window will not affect existing routes, but routes that are subsequently created will be assigned the new default polar file as their boat type. The only way to change the boat type for existing routes is to edit the options for each individual route.

      Normally, the program loads polar data automatically, as needed. For example, if you have a route with boat type J120 and you load a wind grib, then the program will detect that it needs the J120 polar data to calculate the sailing time for the route. If polar data named “J120” has already been loaded, it uses that data. Otherwise, it looks for J120.pol or J120.txt in the polar folders (which you set in the Preferences window) and then loads the data from the file into the program. This is all done quietly in the background with no need for action on your part. You don’t need to load the polar yourself with file->load polar.

      The polar data for a boat type isn’t loaded into the program until it’s needed. Programmers call this “lazy evaluation.” The polar manager only lists the polars that have actually been loaded into the program. You can load additional polars in to examine, however.

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