Underway - Pacific Crossing Notes: A Sailor's Guide to the Coconut Milk Run - page 131

Wrapping Up
To recap: we focus on the essence of celestial navigation by letting electronic tools auto-
mate the tedious sight reduction procedure. Then we turn the traditional approach of using
LOPs from many different bodies on its head by taking a short series of sights of only two
bodies. Applying the median estimator to the resulting data improves our fix accuracy by
reducing random error and the impact of outliers. It also provides valuable feedback for im-
proving our technique by identifying and eliminating systematic errors.
With this approach, we recreational navigators get about 80% of our fixes within four naut-
ical miles of our GPS position and 97% within ten nautical miles. The method proves par-
ticularly useful in higher seas with a pronounced rolling of the boat. While the spread of
the intercept values increases in higher seas, the median remains surprisingly robust.
Perhaps the biggest benefit has been the confidence we developed in our sight taking and
our ability to judge the quality of our sights. As a result, a sometimes frustrating trial-and-
error experience has become a fun pastime in which we can actually see our progress.
The ultimate reward comes when we can switch off the GPS and experience the satisfac-
tion of practicing an old art on our small boat. And who knows? Now that we've got the
important parts down, we may even turn purist and dig out those logarithmic sight reduc-
tion tables again…