This post dedicated to Pam Wall, who consulted with me on Mo’s suit of electronic navigational equipment and who will know, intimately, the foibles of manual navigation.
June 26, 2018
Noon Position: 39 22N 154 00W
Bar: 1023, steady
Sky: Fog, drizzle, then more fog
Cabin Temperature: 69
Water Temperature: 59
Sail: Twins, poled out, running
Noon-to-Noon Miles Made Good: 165
Miles this leg: 1,152
Avg. Miles this leg: 144
Since departing Hawaii, my morning and afternoon sun sights have been way out, like 20 miles out. These are the sextant shots that are timed to the second and that, in concert with the noon sun shot for latitude (not timed), can produce a running fix of one’s latitude and longitude.
Early on I attributed this grand error to the sun itself. Oahu lies at roughly 21 and a half north latitude, and when Mo and I departed, the sun’s own celestial latitude (called declination) was roughly the same. Essentially, we were sailing under the sun in the first few days of our cruise.
The effect of this on one’s sun sights is that the resulting morning, noon and afternoon shot lines don’t cross on the chart in an “x marks the spot” fashion. The noon latitude line runs east to west and the morning and afternoon lines run north and south, creating not the expected cocked hat but rather what looks more like a tic-tac-toe hash, inside of which somewhere one may be.
But in the last week we’ve sailed quickly north, and since June 21, the sun has begun its slow retreat south such that by now my sight workings do produce a cocked hat, of sorts, and it’s still 20 miles wrong.
How could this be? Finding the answer has consumed me.
The February knockdown in the Indian Ocean that broke one of Mo’s pilot house windows also drowned most of her electronics, including the Single Sideband Radio I used for WWV GMT Time Signals. I set my wrist watch to these accurate-to-the-second pings. Since the knockdown I’ve set my wristwatch to the GMT clock on the chart plotter, but I’ve noticed it sometimes skips a beat, and worse, is three to six seconds different from the GMT read-out on one of its other screens.
I factored these differences into my sun sights and it “corrected” my workings a mile or two, but nothing near the 20 miles needed.
So, maybe it’s a problem with the sextant, I reasoned. I did true-up the mirrors in Hawaii. Possibly I did more harm than good. Or maybe it’s that on Monday the weather was really rough, and I couldn’t get the sextant still enough for a good shot–actually, I could barely keep from being washed overboard. Or maybe the overcast of yesterday and the indistinct, “fuzzy” sun are to blame. Or maybe it’s that the fog we have today means the horizon is too close.
All good, all well reasoned, all possible…except that on each of these days my noon shots for latitude were spot on (respectively, out by a mile; out by 2 miles, and today, out by .1 miles…in fog and with an indistinct horizon). So, the problem is not with the sextant or my shooting.
It could well be that my arithmetic in the workings is wrong or maybe the look-ups themselves found the wrong page or the wrong column. I am prone to the simplest of simple errors: adding when I should subtract, carrying a non-existant one, going to the “Contrary” page when I want the “Same” page. But I’ve double and tripple checked for this. Besides, for the 20 mile error to be consistent day to day, I’d have to be making the same error consistently, and it would have to be a whopper.
No, the only answer is that it’s a problem of time. There’s just no other conclusion. But how could the chart plotter be reporting GMT so inaccurately? After all, it uses time to establish my position.
I hold my wristwatch up to the chart plotter and check it against the GMT readout, a thing I have done at least once a day since discovering the problem.
And then I see it.
Well I’ll be hornswoggled with watery grog but if the *minute* hand on the watch isn’t a *full minute* slow!
When I reset the watch in Hawaii, I must have been careless and missed the exact minute of set. All my readings have been a minute off since then.
I quickly redid the day’s shots, incorporating and correcting this error, and I found Mo’s noon position to within a mile.
And there we have a stunning example of the principle of Occam’s Razor, unemployed. The problem wasn’t that a perfectly good sextant had gone out of tune or that time, as managed by a network of satellites, had succumbed to chaos. No, the problem was simpler than that; its source was a $50 wrist watch, and more specifically, its wearer.