LuckGrib supports importing all of the known polar diagram file formats. (If you have a polar file which will not import, please let Craig know about it.)
Sailing polar diagram files can be imported into LuckGrib in several ways.
On the Mac, there is a menu item in the File menu named Import Polar Diagram File… Use that menu item to import a polar diagram file. You can also open the Polar Diagram Manager and use its ability to import a polar file. The vessel settings editor has a menu which allows you to choose the performance settings for a vessel, that menu also allows you to import a polar file.
On an iPhone or iPad, open the Sidebar, and navigate to: Library / Routing / Sailing Polars. On that screen, there is an Import button in the top right corner. Tap the Import button and then select the polar diagram file.
After importing the polar file into the system, it will be available through the vessel performance editors performance menu.