Get an iphone and a waterproof case. Get iRegatta app and sail to all directions so you register your polar for the current wind speed. If you want to know your optimum tacking angle, look at the VMG polar.
It works if wind direction and speed are fairly constant, which is probably not so common though...
Cool app. Pair it with with some
Bluetooth waterproof headphones and you've got yourself a fun little training app.
