Crossing the Archipelago Sea (in The Baltic, in Finland)
with a Nordic Folkboat, here at Gullkrona, alongside the H-boat with the longest yacht name ever.
Utilising Doppler shift, a single GPS-receiver can give not only the position but velocity (speed, direction) of a wave buoy and hence wave direction.
As I read "Research on the Algorithm Model for Measuring Ocean Waves Based on Satellite GPS Signals in China"