I believe I found out why we were having difficulties registering nautical miles (1 tack is .49km). With Min Speed Settings set to 5 knots, it required that you had to gybe on port. Most folks are tacking on port to get back up wind so we do dip below 5 knots which in turn causes the GT-31 to stop recording. Below is a screen shot of two different sessions but one is set to record continuously.
You can see some missing tracks in mid tack when a min speed value is set.
Now the question to whether turning min speed off will affect 1 hour
speeds. Doesn't look like it will affect it that much...I guess it is better to have a nautical mile and hour reading than having just one reading!