Try this multi purpose refreshment, friend enhancer and wind meter.
Take bottle of beer, drink beer, hold bottle to wind, if it starts whistling start rigging. If not whistling repeat until bottle starts whistling or you no longer remember why you were there in the first place

The higher the pitch the stronger the wind, bottle will start whistling between 16 - 18 knots.
Thats why I'm never without a trusty beer o meter in my hand


Elmo method for non drinkers:
Place empty flavoured milk carton on table, when the carton blows off table it's 18 knots !!!
I guarantee both of these methods are far more accurate than any IPhone app.