We were going to Santa Cruise Island about 50 miles and 11 hours out. I turned all instruments off and had only the compass to guide me. Did DED reconing using a guessing system for speed and drift. Only had the helm compass, a paper chart and the ships clock. After 9 hours was less than 1 mile off my deduced position when I took the cover off the chartplotter.
I thought that was pretty good. It was only an exercise but I believe a necessary one. A bit like doing man overboard drills.