This has turned into a great topic. I forgot that radar
can calculate speed also. In a sense, radar
can also be a back up for a failed GPS
. I'm so low tech that I had never heard of doppler units. I probably could not afford one anyways. I also wonder why the manufacturers of knot
meters do not build them to be calibrated at low speed (say 2 knots) and a higher speed (say 6+ knots). This would certainly correct the problem I experienced. On Faiaoahe we were offshore
of the Ca. coast heading south towards tropical depression "Boris" this summer. With 50% of the Yankee only, the log read 6-7 knots. We were probably doing 8+. The vessel was doing fine but if I had known, I would have switched to the staysail.