Way back in the early 2000's when the Macquarie Innovation team decided they wanted to win back and improve on their previous Yellow Pages Outright WSSRC World Speed Sailing Record, they enlisted researchers from RMIT to see if they could use a GPS system to replace their previous video camera based timing system. They found there were many advantages with GPS and were instrumental in getting GPS timing measurement approved for WSSRC records. The GPS system they used was a Survey Grade, differential corrected system by Trimble. This system was very large and very expensive at that time compared with current technology. This RMIT paper describes a lot of how they did it (the rowing part is not as much interest to us):
www.researchgate.net/publication/239768624_GNSS_for_sports_sailing_and_rowing_perspectives
I just found the full detailed paper with all the Math and method in it. Good bedtime reading for insomniacs. 
www.researchgate.net/publication/267299688_SURVEYORS_GPS_AND_THE_WORLD_SAILING_SPEED_RECORD
