NavList:

Greg Rudzinski, you wrote:
"Made possible by checking cross track error using naked eye horizon lower limb sun observations each morning for the four day return trip. The coincidence is that the horizon morning observation LOPs plot parallel to the vessels charted rhumb line track between Venus Point and Pearl Harbor."

Aha! I ran some special tutorials for the Marion-Bermuda Race this past Spring, and this was a key component. The Sun at sunrise (LL rise recommended) was almost exactly perpendicular to the Newport-Bermuda rhumbline which is used as a standard reference line for this race (thanks to the existence of a special NOAA chart apparently created specifically for the wealthy yacht traffic on this route). A sunrise sight like this --which requires no sextant, only a good watch-- can be a nice check on cross-track deviation, though it's subject to errors often as large as five miles from anomalous refraction, and it should definitely be adjusted for deviations from standard temperature and pressure. Working it is easy enough, either as a normal sight, or from pre-computed times. If you have a pre-computed time (which I provided for the racers since we knew exactly what days they would be at sea as well as their approximate locations on those dates), then for every four seconds the Sun rises ahead of schedule, you're one minute of longitude east of the rhumbline. So easy! A nice thing about this LOP, like any sight abeam, is that there is no adjustment for run during the day, unless you end up sailing on a non-perpendicular course for better winds, currents, weather, etc. If you happen to get another Sun sight later in the day, a line of position parallel to true course advances on top of itself (no advancing at all).

Incidentally, I still recommend using the sextant for that sunrise observation for the magnification and the shades. Just set it to zero and it provides a sharp, clear view of the instant of sunrise. I also recommend that if the Sun looks unusually "ragged" the observation should probably be ignored since that's an indication of anomalous refraction.

Frank Reed