A Note on Celestial Navigation and a Frigate Bird

Day 159/37

Noon Position: 06 58S 154 05W

Course/Speed: N5-6

Wind: E15-18 (20 – 25 all afternoon)

Bar: 1011, falling

Sea: E5

Sky: Cumulus to 20%

Cabin Temperature: 89

Water Temperature: 84

Sail: #2 jib full; main one reef, close reaching (double reefs in the afternoon)

Noon-to-Noon Miles Made Good: 137

Miles this leg: 4,512

Avg. Miles this leg: 122

Miles since departure: 21,619

Aeolus is a trickster god, it should be admitted. On the 28th day, he created the The Trade Winds, saying, “Blow trade will these winds. Now go forth and multiply.” And they do blow trade. But man, do they shift in velocity something fierce. I’ve reefed and un-reefed thrice today, which I think must entertain Aeolus. I sure hope he’s watching.

That tired complaint to one side, it’s been a fine day on Moli, for today my sun sights yielded an accurate fix.

If find celestial navigation to be something like the opposite of going to the dentist; it’s fun to do; but the procedure is eminently forgettable. Each time I go back at it (I did sun sights all the way down the Pacific in November and December of last year–and not since), it usually takes me three or so days of sights to work out the kinks. This time it was *just* three days.

What I know I’ve learned from Tom Cunliffe’s little book titled simply Celestial Navigation, and the method I’m most comfortable with goes by the name “Sun-Run-Sun.” In brief, it requires three shots of the sun throughout the day, one mid morning and another mid afternoon to fix lines of position that include longitude, and a noon shot line of position for latitude. The “run” refers to the running fix in pilotage, only here one is running up to noon and back to noon the morning and afternoon lines of position from the sun.

Beyond the taking of the sights themselves, there are only six steps to the computation, but these require eleven look-ups. By “look-ups” I mean eleven bits of additional information needed to make the computation possible–seven in the Almanac and four in the Sight Reduction Tables.

I use the Nautical Almanac produced by the UK Hydrographic office and Sight Reduction Tables for Air Navigation, known more broadly as HO 249. (These were produced for WWII bomber navigators; they are simpler and quicker to use than the Navy’s HO 229, and they are wee bit less accurate–a fair trade on a bounding boat.) Having got all one’s ducks in a row, the math is simple addition, subtraction and division. No calculator needed.

But holy cow, are there ever opportunities for error. Wrong date, inaccurate read of the time, bad conversion of local time to GMT; bad sight taking, bad reading of the altitude off the sextant; wrong page in the book(s), number transposition, sloppy conversion of base 100 to base 60 (when finding local noon); failure to remember that most addition/subtraction is base 60 (it is time, after all); wrong latitude name in the sight reduction tables; wrong column; wrong column, wrong column.

Then there’s taking the sight itself. The boat is acting like a washing machine that’s just swallowed an elephant, this while you are trying to get an altitude accurate to the second off a body so far away it takes eight minutes for light to travel from it to you.

But today, success.

Local Noon position by

GPS: 06 56S 154 04W

SEXTANT: 06 57S 154 07W

Someone on the site asked how often I use my sextant. I think the answer is “not often enough.” It’s immensely rewarding to find one’s position on the globe the “old way” (the *only* way until recent decades).  And once the procedure is habit, it’s not hard to keep it up. But when the going gets rough, it’s the first thing to fall away…because it can. The chart plotter offers a position to the 100ths of a second every second of the day. And I don’t even have to push a button.

This is one reason I admire the sailors in the Golden Globe Race that commences in a month or two. Those singlehanders, departing from Plymouth for a non-stop lap of the world via the Southern Ocean, will find their position by sextant or not at all.

First lone frigate bird sighting today. Easy to identify. They are the only pelagic that soars high up with the clouds.

8 Comments on “A Note on Celestial Navigation and a Frigate Bird

  1. Randall! I love every single post and feel I am right there with you and MO! In 1967, when Andy Wall sailed Little 30
    Timber CARRONADE, celestial Navigation and DR were all he had to round Cape Horn! And our circumnavigation in 1985 had a schedule much like yours every day the sun could be seen! Morning, noon, and afternoon! No electronics in those wonderful days! So I know all it takes to navigate with the sextant!! But it was easier for us as I could take the time for each shot when Andy would yell to me sitting at the chart table “Mark!”
    Your log gives me so many happy memories! THANK YOU!

    • Pam your comments on this blog elevate it from great to excellent, grand!!!!

  2. Recalibrate your chart plotter to match your sextant sights. 😉

  3. Thank you Randall. Great post. And it makes me feel much better that I’m not the only one who has to relearn and relearn how to do celestial, since I use it too infrequently.

  4. Oh yes, me too. But I have an additional problem to getting rusty and forgetting. The close work at the tables makes me seasick!! My bets passage is when I found mile-long Lord Howe island right on schedule after sailing 1,000 miles from Fiji. Haven’t had a successful celestial navigation since!!!

    And I’m with Pat, getting the site and the time by yourself is REALLY HARD!! Mark!

    • Hi Mary, I know just what you go through with celestial navigation. My husband taught me and I was lucky to have such an understanding teacher. Maybe he understood because of the first ocean passage he made when he was 22 years old aboard his tiny 30 foot sloop. His passage departed Pittwater Australia, his home port, in 1965 bound for Lord Howe Island. He used Mary Blewitts little book to teach himself how to celestial navigate. In the beginning you can imagine his worry and frustration getting those sights, and time ticks, Mark!!! and computing them to have a daily position. He was so concerned about his accuracy that when he heard and saw a seaplane overhead he hoped it was on its way to LHI! Andy quickly took a bearing on the plane before it disappeared and he followed its compass course the remainder of the passage along with his newly acquired celestial navigation. When that smudge of land first appeared, where it was supposed to be, his joy and surprise were unbound,,, You have to use every possible navigation aid to be a good navigator!!!

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