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Trade Winds and Celestial Navigation

By Kate “Bob” Addison

The first Monday in January finds Picton Castle sailing merrily along in the South Pacific at 10º17’S 108º08’W. There is a steady Force 5 breeze on the port quarter which makes us all very happy, as well as driving us along at a steady 6 to 7 knots. Our compass course is SWxS and we are on a port tack, heeling over to leeward six degrees or so and rolling very gently – excellent conditions for learning and studying, ships’ work, and also good for sleeping, especially for those us with starboard bunks.

The weather is bright and sunny and fluffy cumulus clouds are rolling across the sky, dappling the decks with sunshine and making the bright blue ocean sparkle. We have bent on and set the flying jib (all the way forward) and the gaff topsail (all the way aft) and the royal sails nearly 100 feet up are now routinely being left on overnight. This reliable trade wind weather is just about perfect for a square rigged sailing ship – she practically purrs as she glides through the water, pushed along by the pressure of the spread of white canvas. “How silently they do their work!”

The square sails have all had their buntlines ‘nipped’ so that they don’t chafe on the sail when they’re set in the same position for an extended period of time, and it’s possible to go a whole watch of four hours without touching the sails. Plenty else going on though – rigging aloft and alow, sail making on the quarterdeck, engineering, woodwork, and maintenance all over – today the handrails on the aft deckhouse got a coat of black, which looks very sharp against the stone deckhouse – lessons in tidy painting obviously paid off!

Celestial navigation is progressing well – twice a day a different gang gathers for a celestial navigation workshop on the quarterdeck or the main hatch. Morning lessons are with mate Michael and the afternoons with second mate Sam. And then every day at noon or thereabouts, a self-selected group gathers on foc’sle head or quarter deck to practice with a sextant – bringing the sun down to the horizon, waiting ’til the sun ‘hangs’ for a second to get the exact time of local apparent noon and measuring the angle at that time, and then using the angle to work out our latitude. Sun runs are next and then stars – we’ll have longitude down before you know it.

We don’t have the same problem finding longitude that the early navigators did because exact time is so easy to determine accurately now. It blows my mind that my $10 quartz wrist watch is so accurate – keeps time to within seconds even after weeks at sea. And even if it wasn’t that accurate I could just use the time on the GPS. Of course I could just look up our position on the GPS, but that wouldn’t be the point at all. Celestial is WAY cooler, and this is the perfect passage to practice – day after day of steady progress across the Pacific with the seas small, the horizon mostly clear and the skies often cloudless.

Very basically the theory is that if you know what position a celestial body will appear at a certain point in time and space then you can work out your own position by measuring the difference between where it should be and where it actually is at that exact time. So we know the time relative to Grenwich, London, and we also have books of tables that give the computed position of the most important celestial bodies. These have been calculated and tabulated for sun, moon, planets and stars at every point on the planet for every moment of time each year – a fact which makes me very happy. There must have been so much cooperation between people, so much detailed, accurate work and smart thinking to first build up these tables – and to create them first without a computer or even a pocket calculator. It’s also sort of comforting to me to think that the stars and planets aren’t just doing whatever they feel like, but they are all processing across the skies in well ordered patterns according to the daily dictats of the almanac. Somehow very British of them to be so predictable. But mostly it makes me happy that I can do celestial navigation without having to solve any tricky spherical trigonometry, or even so much as look at a logarithm.

But so much for being able to solve the maths – it’s no use at all if you don’t have good skills with a sextant to get an accurate reading to start with, and it’s suprisingly difficult to get a good reading while standing on a rolling deck. The sun has been almost direct ahead of the ship at noon the last few days too, so the pesky sails keep getting in the way, and the other students lined up along the rail too – nothing more frustrating than bringing the sun down towards the horizon and then realising you’re actually focussing on someone else’s back and not the horizon at all. All frustrations shared by many generations of novice navigators before us no doubt.

celestial workshop
Noon sights
Signe s Danish Birthday
working in the headrig

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