Antique Navigation

Where Next?
Bob Williams
Tue 25 Jan 2011 21:20

Noon Position: 11 57.0 S 127 46.5 W
Course: 295 Speed: 5.5 Knots
Wind: East F3-4 Gentle to Moderate breeze
Weather: Sunny, warm
Day’s Run (24 h 42 m): 149 miles



Now that I have gotten my antique trailing log working again to a reasonable degree of accuracy I have decided to refresh myself with a bit of antique navigation. I broke the antique sextant out of its case and shot a set of stars last night which came out well except for my sights of Jupiter. I tried working back through them to find out the error but with no success. I had taken three sights of the unmistakeable planet and they were all pretty close to one another, only they were a good 30 miles from where the other four stars I had taken placed me (three sights of each which makes for 12 position lines – I know Andy and Jan are following this). I might have misread the deck watch, this was not an uncommon problem back in the days of analogue watches when the time was close to the minute, but this seems unlikely as my watch is not in fact an antique analogue but digital (I am not a complete Luddite, I even use a programmable calculator to reduce my sights), and in any event one minute of time is 15 minutes of longitude, not 30. Hmm? Curious. We will try again tonight.

I intend to complete the rest of this passage without GPS, turned it off yesterday, so my noon to noon runs will now be the traditional local noon time, i.e. meridian passage when the sun is at its zenith. As we are travelling west this means my days will be slightly longer then 24 hours. (Back in Magellan's day it took the astronomers quite a while to work out why the few argonauts that made it back had lost a day in their accounts.)

I might even try for a lunar distance in a day or so, never done one of those before.

25 days out and five days to the Marquesas.

All is well.