Any chance you could consider adding a full 360 Degree dial with needle... like a compass to your pi controls? Iv already written python code to take the NMEA code from my yacht, interpret it, and display it on my iPad as text. However wind direction, apparent wind, heading etc need to be displayed as a graphic. Your app looks perfect for this if I were able to show this graphically on the iPad.
Once I'v completed the graphical front end I'm sure many people with boats will wish to utilise the software. It only requires a £3 interface available from eBay and a mini usb wifi dongle to take all the data from NMEA 183 (standard on most boats) and broadcast it to any iPhone / iPad. The alternatives a the moment cost hundreds.