Sextant: A Voyage Guided by the Stars and the Men Who Mapped the World’s Oceans

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From my father I learned something about surveying and the use of trigonometry – the mathematical technique for deducing the size of the unknown angles and sides of a triangle from measurements of those that are known. On our walks in the New Forest we sometimes came across the concrete triangulation pillars on which the British Ordnance Survey maps were based. Each pillar formed the corner of a triangle from which the other two corners were visible. Starting from a very accurately measured baseline, a network of such triangles extended across the whole country. By measuring the angles between the pillars using a theodolite, surveyors could determine the relative positions of each pillar with great accuracy, thereby providing the map-makers with an array of fixed points on which to build. In those days this system was still the key to land-based cartography.

Every marine chart was liberally sprinkled with ‘soundings’ – numbers representing the depth of water in old-fashioned fathoms (1 fathom to 6 feet), which crowded in even greater profusion round hazardous patches of sea. Particularly sinister were the places in the mid-ocean depths where a tight cluster indicated an isolated shoal – perhaps the tip of a ‘sea mount’ that did not quite break the surface. The Chaucer Bank, some 250 miles north of the Azores in the middle of the North Atlantic, is an example. On Admiralty chart no. 4009 (North Atlantic Ocean – Northern Portion, published in 1970) it rose up to a ‘reported’ minimum depth of 13 fathoms from waters that slide down rapidly to 1,000 fathoms or more. In heavy weather, seas would break on such a shoal – an alarming sight so far from land, and a potential hazard too. Before the advent of the electronic echo sounder in the 1920s all these soundings would have been taken with lead-lines – nothing more than a lump of lead on the end of a long, calibrated rope or wire. Triangulation could have been used the fix the positions of soundings along the coast, but what about those offshore, far out of sight of land? Of the vital part the sextant had played in hydrography – the mapping of the seas – I had as yet no idea.

As a teenager I sailed to Normandy and Brittany and around the west coasts of Ireland and Scotland. These excursions offered plenty of navigational challenges – the English Channel with its strong tidal currents and heavy shipping traffic is a dangerous stretch of water and the many rocky shoals of Brittany, Ireland and Scotland demand respect – but they did not call for the use of a sextant. Instead we relied on dead reckoning (DR – using the distance travelled and the course followed to estimate your position) corrected by radio direction-finding (RDF – fixing the boat’s position by taking compass bearings of radio beacons). If sailing at night, compass bearings of lighthouses were helpful too. While these methods worked well enough for short coastal passages, I wanted to know more: I was determined that one day I would learn how to navigate the open ocean by the sun and stars. I had not yet even seen a sextant, but the mysteries of celestial navigation already had me under their spell.

*

Just ten years after seeing Mutiny on the Bounty I got my first chance to handle a sextant when a family friend invited me to help him sail across the North Atlantic in his 35-foot sloop, Saecwen.

Colin McMullen was a retired Royal Navy captain and like many naval officers he was easy-going, relaxed and charming – useful if not essential qualities when sharing cramped accommodation for any length of time. Colin loved nothing better than an impromptu party. On the slightest pretext he would get out his accordion and start a ‘sing-song’, and if he was in particularly high spirits he might even put on a false beard and impersonate an ancient mariner with a strong west-country accent.

Colin was also fond of practical jokes, one of which almost cost him his life. As a young midshipman on board a small yacht being towed by a much larger vessel, he decided it would be amusing to climb along the tow rope and appear – as if by magic – on the deck of the mother ship. This meant scrambling along a heavy hawser, the middle of which frequently dipped beneath the surface of the sea. Colin was barely able to hold his breath long enough and nearly lost his grip as the cold, fast-moving water tugged at his submerged body. He was carpeted for this crazy escapade, but in the Royal Navy of the 1920s there was room for colourful characters, and it did his career no harm.

Colin had been messing about in boats since his childhood days at Waterville in County Kerry during the First World War. When he was posted to Malta in the 1930s he was given the enviable task of delivering the Commander-in-Chief’s official yacht to Venice, and I remember him talking rapturously about the summer days he spent along the Croatian coast aboard this large and elegant vessel. Most of his sailing, however, had been on a much more modest scale – notably in a small yacht called Fidget that he shared for a time with a group of fellow naval officers.

Colin bought Saecwen after retiring from the navy, and I first crewed for him when the two of us sailed her along the south coast of England from Dartmouth to her home port, Lymington, in early January 1972. It was an overnight trip and the weather was clear, cold and windless. As we motored slowly across the wide expanse of Lyme Bay I watched the ‘loom’ of French lighthouses, one of which – on the notorious Roches Douvres reef off the coast of Brittany – was nearly 80 miles away, far beyond the range at which it would normally be visible. The distant pencil beam of light rose briefly from below the horizon, sweeping up and over like the headlamps of a car making a sharp turn on the far side of a hill.

In the middle of my watch I heard the hatch slide back, and there was Colin – who should have been asleep – with two cups of hot cocoa. While I steered we sat together looking up at the night sky, our breath smoking in the cold. It was then that we first talked about celestial navigation. Colin pointed out the stars to me and recalled his days as a young naval cadet, just after the First World War, when learning to handle a sextant and plot a line of position had been nothing but a chore. Now he was planning a transatlantic cruise in Saecwen and was looking forward to brushing up his old skills. Nothing was said at the time, but later that year Colin asked if I might be free for six weeks or so the following summer; the trip to America was going ahead and he was looking for crew on the return voyage to England. As a university student with time to spare I eagerly accepted the invitation: here was a chance not only to cross an ocean under sail but also to learn the art of celestial navigation from a professional whom I admired. But transatlantic passages in small boats were not yet the fairly routine events they have since become. Looking back I am amazed that my mother, who had been widowed not long before, raised no objections. She must have felt the risks were worth taking.

*

On a sticky evening in early July 1973 I arrived at Falmouth, a small town on the coast just north of Portland, Maine. It was my first visit to the USA, and I had travelled up from New York on the Greyhound bus. The licence plates on the cars announced that I was in ‘Vacationland’, the temperature was in the 90s and the humidity was only slightly less than in Manhattan, though the still air was refreshingly clean. From the bus terminal I took a cab to the Portland Yacht Club, and as I walked down the jetty I caught sight of Saecwen lying at a mooring only 50 yards away. Rocky islands covered with hemlock and spruce lay further offshore. Colin was watching out for me and pulled across at once in the rowing dinghy to pick me up. It was strange to step aboard Saecwen again in such different surroundings, but as the deck gently rocked beneath my feet I felt almost as if I had come home. I slung my bag into the starboard quarter berth where I was to sleep for the coming weeks, absorbed the familiar smells, and came up on deck where Colin handed me a can of beer – very welcome in that heat. He was not alone on board Saecwen. There were two other crew members at this stage – Colin’s sister, Louise de Mowbray, and his cousin, Alexa Du Vivier, who was just seventeen. We talked about Saecwen’s voyage out across the Atlantic – it had been tough going, with several gales, and one member of the crew had suffered so badly from seasickness that he had been forced to leave the boat in the Azores. Transatlantic passages by small yachts were then sufficiently rare that Saecwen’s British ensign had caused a lot of excitement when she arrived in Gloucester, Massachusetts. The news media had soon discovered Colin who, playing the role of old British sea-dog to perfection, had been interviewed on TV and radio. He was delighted by all the attention.

We set sail the next morning. Wherever Saecwen dropped anchor, as we cruised north and east through the rocky, wooded islands that sprinkle the coast of Maine, complete strangers appeared offering food, showers and lifts to the shops – and we did not hesitate to accept. I started to read Samuel Eliot Morison’s classic account of the early European voyages of discovery to the Americas, which I found on board. I learned – to my surprise – that it was French rather than British mariners who had first properly charted the seaboard along which we were now sailing. The north-east coast of America is notorious for its cold fogs, but luckily we encountered little until we set out across the Bay of Fundy, from Grand Manan Island, past Yarmouth towards Cape Sable at the southern end of Nova Scotia. Fog is strangely disorienting and at times it was so thick that we could hardly see the bows of the boat from the cockpit. Colin was busy plotting our position by RDF as we rounded Cape Sable by night when we had a bizarre encounter with a ferry whose approach first became apparent when we heard the distant beat of pop music. It grew steadily louder until at last the thump-thump of the ship’s propellers also became audible. By now we were really worried, but there was little we could do to reduce the risk of a collision apart from tooting feebly on our small foghorn, all too well aware that we had little or no chance of being heard. Suddenly the blurry outline of a big ship, brilliantly illuminated, emerged from the fog, and the air was filled, bizarrely, with Bill Haley’s ‘Rock Around the Clock’.

The ferry shot past us at a distance of no more than a quarter of a mile, disappearing again very quickly, while the music gradually faded. We were carrying a radar reflector and ought to have been plainly visible on the ship’s radar, but we had the uncomfortable feeling that no one had seen us – and we knew that if we had been run down, the slight bump would probably have passed unnoticed. There was an inflatable life raft lashed to the foredeck, but even if we could have launched it in time, in those cold waters rescue would have had to come quickly. On the open sea, collision is the biggest risk faced by a well-managed yacht, as we were dramatically reminded a few weeks later, far out in the Atlantic.

*

Our last port of call was the magnificent and historic natural harbour of Halifax, Nova Scotia, where we spent a week busily preparing for the crossing. Louise now flew home, leaving just Colin, Alexa and me aboard Saecwen.

Halifax served as the Royal Navy’s main base in America during the Seven Years’ War, a pan-European conflict that formally broke out in 1756 (though hostilities between the British and French and their native allies had already begun in America) and was fought in many different parts of the world. It was here that James Cook – who was to become one of the greatest European explorers – began to learn the science of surveying from Samuel Holland, a military engineer serving with General Wolfe.

In 1759 Cook played a key part in the daring survey work in open boats on the narrow and dangerous ‘Traverses’ of the St Lawrence River below Quebec City. The safe channels having been marked, the British fleet was able to pass the Traverses without a single loss, thereby permitting Wolfe to land his forces upstream of Quebec. The French Governor angrily commented: ‘The enemy have passed 60 ships of war where we dare not risk a vessel of 100 tons by night or day.’

Wolfe and his French opposite number, Montcalm, both lost their lives in the famous battle on the Plains of Abraham that followed, but Quebec fell to the British, and the final expulsion of the French from North America soon followed.

Cook, who had not yet received an officer’s commission, continued surveying throughout his time on the American coast and in 1761 he was given a bonus of £50 ‘in consideration of his indefatigable Industry in making himself Master of the Pilotage of the River St Lawrence &c’ – a most unusual distinction.

The following year, while assisting in the recapture of the port of St John’s, Newfoundland, Cook worked with another remarkable military engineer, Joseph DesBarres, and carried out important surveys that brought him to the attention of the Admiralty in London.

He was starting to make his name.

*

Colin’s original plan had been to carry on to St John’s, Newfoundland, calling on the way at the small islands of St Pierre and Miquelon – the last remaining French outposts in North America, which Cook surveyed in 1763

just before they were returned to France at the end of the Seven Years’ War. However, the icebergs emerging from the Arctic had drifted much further south than usual in the summer of 1973, and we decided that it was wiser not to go any further north. Dodging icebergs in a wooden boat is risky. The most dangerous kind are the ‘growlers’ – small pieces of ice but still weighing many tons, completely awash and therefore almost invisible above the surface – and bumping into one of them might have brought our voyage to a quick and fatal conclusion.

The last couple of days in Halifax were filled with lists. There were loads of provisions to buy, including a whole chicken in a tin to be saved for a special occasion. Everything had to be carefully stowed in one of Saecwen’s many lockers, and a record kept of its location. Having removed their paper labels – which might well get washed off – we marked the tinned goods with a waterproof felt pen. Fresh vegetables and fruit went into cargo nets hanging from the low cabin roof. We checked the rigging for signs of wear, and I was hoisted in a bosun’s chair to make sure that all was well at the masthead. Looking down from that height Saecwen seemed very small indeed. Finally we did our laundry, filled up with diesel fuel, paid the harbour dues and said farewell to our Canadian friends. Early the next day we topped up the water tank, cast off and motored down the harbour.

The taking of Departure [wrote Joseph Conrad], if not the last sight of the land, is, perhaps the last professional recognition of the land on the part of a sailor … It is not the ship that takes her departure; the seaman takes his Departure by means of cross-bearings which fix the place of the first tiny pencil-cross on the white expanse of the track chart, where the ship’s position at noon shall be marked by just such another tiny pencil-cross for every day of her passage.

We took our Departure from a whistle buoy just off the harbour entrance. Thousands of miles of ocean and weeks of sailing lay ahead of us. We had no way of telling what weather we might face and would not be able to receive forecasts. We could only keep an eye on the barometer and hope for the best. I felt like an actor stepping on to the stage at the start of a big performance as I hauled up the sails. We hardened the sheets and Colin cut the engine. Apart from the sound of the wind and waves all was quiet. Saecwen heeled to the south-easterly breeze and began to dip her bows into the Atlantic swells. Cold spray rattled over my oilskins. Here we go, I said to myself.

Chapter 2 (#ulink_a7e686d8-0230-54d3-9378-01a094ee0f46)

First Sight (#ulink_a7e686d8-0230-54d3-9378-01a094ee0f46)

Days 1–2: Didn’t sleep much. Up at 0730 for breakfast very conscious it would be the last meal on dry land for a while. Took shower in the club house. Our Canadian friends came to see us off and we set sail at 0930 for England. There was little if any wind and a thick cold fog soon rolled in. At 1115 we heard the outer whistle buoy close by. The wind picked up from SE about 4–5 but with a confused sea. Alexa felt sick and went below and I started feeling queasy too.

Colin and I had tinned beef stew and potatoes for supper. Now seem to be getting my sea-legs back but Alexa still curled up in the fo’c’s’l out of action neither eating nor drinking.

I took the watch from midnight until 0400. The far end of my sleeping bag was soaking wet when I turned in. Up again at 0800. Dull, grey morning, but no more fog.

Bumpy seas, as we plugged on to the south of Sable Island under reefed main. At 1200 things brightened up and the sun came out. Wind eased to force 3. Put up genoa [the largest foresail] and got a bit more speed. Had a nap before supper, then took watch from 2000 until midnight when the skies started to clear and the stars shone brightly all around.

The thick, chilling fog that closed around us as we left Halifax reduced our world to a damp, grey circle no more than 50 yards across. Once we were clear of the land it lifted, but the sea was lumpy and the sky overcast. Shearwaters glided quickly past us on stiff wings eyeing us coldly, and stormy petrels fluttered over the surface, dabbling their feet in the water, taking no notice of us at all. The spray flew back, wetting our faces and stinging our eyes, as we butted, close-hauled, through the short, steep waves, out into the Atlantic.

Coming off watch on the first night out I curled up at the far end of my bunk trying to keep clear of the drips coming through the deck just above me. This is no fun, I reflected – no fun at all. I am cold and scared, and there are nearly 3,000 miles of ocean ahead of us. What the hell am I doing here? Why did I agree to come on this trip? I kept thinking of all the comforts I had left behind, especially warmth and dry clothes. The leaks would eventually stop – more or less – but only when the sun-baked teak was thoroughly soaked and the seams had tightened up.

The following day we crossed the edge of the continental shelf south-east of Sable Island, a menacing sliver of sand and grass that lies right in the shipping lanes – the scene of countless wrecks. Perhaps the first of these to be recorded (by the great compiler of accounts of early voyages, Hakluyt)

occurred in August 1583, when one of the vessels in a small squadron led by the Elizabethan adventurer Sir Humphrey Gilbert ran aground there and broke up. Her crew suffered terribly from thirst and hunger before they reached the coast of Nova Scotia in an open boat. There they were rescued by Basque fishermen (who were by then routinely taking cod from the Grand Banks) and eventually managed to get back to Europe – unlike Gilbert who, having coolly turned his back on his shipwrecked companions, was lost on the return voyage.

Sable Island is a desolate spot, inhabited only by wild ponies and sometimes a few research scientists, with a lighthouse at either end. Colin – who relished a difficult pilotage challenge

– had been planning to land there, but even he did not feel like making the detour in these conditions. I was quietly relieved. The first accurate chart of Sable Island was published in 1779 by Cook’s mentor, DesBarres. From 1763 to 1773 DesBarres charted the heavily indented coast of Nova Scotia, and he devoted two summers to Sable Island alone. Apparently the surf often broke ‘mast high’ on the two sand bars at either end of the main island, which were ‘strewn with wrecks for seven leagues’ (21 miles).

It was difficult and dangerous work, but of vital importance, and DesBarres’ chart was one of the first to show longitudes (a word that Colin taught me to pronounce – naval fashion – with a soft ‘g’) based on the Greenwich meridian.

We had now reached the real ocean, where the seabed plunges from a few hundred feet in depth to ten or twenty thousand. The ‘abyssal plain’ stretched out gloomily beneath us. The Canadian Navy had promised us that no icebergs would drift this far south, so the only likely hazards from now on – apart from bad weather – were other vessels. Nevertheless, it was disconcerting to know that we were suspended over several vertical miles of water, kept afloat only by an inch or two of wood.

Standing watch alone on the second night out, I was confronted by an overwhelming sight: half the visible universe, velvet black from horizon to horizon, filled with the brightest stars I had ever seen. Their brilliance was undimmed by the orange glow of man-made light that veils the skies over so much of the land and they seemed infinitely numerous. Three stars, named by the old Arab astronomers, formed a brilliant triangle above us, with the Milky Way – a glowing river of light – running among them: Vega, the falling eagle; Deneb, the tail of the hen; and Altair, the flying eagle.

The light from the nearest of them had taken sixteen years to reach my eyes. Very occasionally, a shooting star slid soundlessly across the blackness, momentarily animating a spectacle of timeless grandeur and serenity.

As we sailed into the Atlantic, leaving the land further and further astern, I watched the night sky as I had never done before. I recognized some of the main constellations, and, with the help of a star chart, picked out a few of the fifty-odd ‘navigational stars’ whose coordinates are listed in the Nautical Almanac. Aldebaran, Alkaid, Alioth, Antares, Arcturus, Capella, Mirfak – as well as the three stars of the so-called Summer Triangle – were all in sight. The planet Jupiter shone brightly, low in the south east, while Mars rose later, to be followed shortly before dawn by Saturn. On Colin’s advice I was reading Mary Blewitt’s classic introduction to celestial navigation for yachtsmen,

and a solitary four-hour watch gave me time to watch how the heavens moved. Above me the entire night sky, with all its stars, was slowly revolving anticlockwise around a stationary Polaris. Stars lying closest to the northern celestial pole (the point vertically above the geographical north pole, or in its zenith) never touched the horizon, while the others rose at different points along the eastern horizon, just like the sun by day, climbing up in long majestic arcs before declining slowly in the west. The poet Homer had closely observed the same phenomenon early in the first millennium BCE, as this passage from The Odyssey reveals:

[Calypso] gave him a warm, fair wind, and Odysseus joyfully spread his sail before it, while he sat and steered skillfully with the stern oar. He never allowed sleep to close his eyes, but kept them fixed on the Pleiades, on Arcturus that sets so late, and on the Great Bear … which revolves, keeping watch on Orion, alone never dipping into the stream of Okeanos – for Calypso had told him to keep it on his left.

I knew, of course, that this celestial motion was in a sense unreal – that it was the earth that turned while the distant stars maintained their imperturbable stillness – but the illusion is too powerful to resist. The earth remains firmly at the centre of the sailor’s universe, just as it did for the Greek astronomer Ptolemy in the second century CE. It is easy to understand how difficult it was for people of the sixteenth and seventeenth centuries to adapt to the heliocentric view of the universe, and for the purposes of the working navigator the Copernican revolution might never have occurred.

*

Day 3: Came on watch at 0400. A fabulous dawn with scarcely a cloud in sight. On a close reach under full main and genoa making 5–6 knots. The seas were much calmer and there was a striking change of colour. Instead of a dull green, the water is now an amazing sparkling azure. Also much warmer – the Gulf Stream. Alexa is feeling better. The sun shone brightly all day and we had bread and cheese for lunch with beer.

Took a meridian altitude with the sextant – my first. Latitude 43° 17' N.

Colin cooked another excellent stew for supper and we all had some whisky. Everyone cheerful.

Though I was very sleepy, the brilliant light and warmth instantly lifted my spirits. The wind had shifted into the south and we were sailing fast, surging smoothly across the waves rather than crashing through them. At last the decks were dry and we could do without oilskins.

We had crossed the ‘Cold Wall’ that marks the division between the frigid, soupy Labrador Current that pours southwards out of the Arctic and the vast body of crystalline, lapis-lazuli-blue water that surges out of the Gulf of Mexico between Cuba and Florida and sweeps northward off the east coast of the USA. The volume of the Gulf Stream is so huge that it retains its separate character until well out into the Atlantic, and its vital warming influence is felt across the whole of northern Europe.

A hundred yards ahead of us, dozens of shearwaters were diving on a shoal of fish, and suddenly the surface of the water exploded in their midst: for a startled moment I thought a missile had been launched from a submarine. An enormous streamlined shape emerged, rising at least 10 feet in the air. Turning and catching the sun, its flank flashed silver, before it crashed clumsily back into the sea in a colossal shower of spray. I had never seen such an enormous fish – it was a tuna, perhaps half a ton in weight, a seaborne sprinter that could keep pace with a cheetah. The astonishing spectacle lasted only a couple of seconds. Soon the small fry that had attracted the predators had been consumed, and all was still again.

As the sun approached its highest point above the southern horizon, Colin appeared in the main hatch, his silver hair sticking out in all directions, wearing an old guernsey jumper that was full of holes. In his hands was the sextant that had, until now, lain unused in the cabin down below, firmly secured in its square wooden box. Before handing it to me Colin warned me with unusual solemnity never, ever to drop it. ‘Care of the sextant’ was a serious matter: it was a precision instrument and our lives depended on its accuracy. My first lesson in celestial navigation was about to start.

There are many kinds of sextant, and they come in many different sizes – from pocket ones just a few inches across to heavyweight models on a much grander scale. And many materials have been employed in making them, from brass and steel to plastic and even cardboard. The essential design, however, has varied little since the eighteenth century, and a good sextant has the reassuring heft and feel of something really well made. With familiarity comes the recognition that this is an instrument perfectly adapted to its purpose: a solution to a practical problem so elegant and efficient as to be quite simply beautiful. But although I had studied a diagram, the sextant now in my hands was bafflingly unfamiliar. Attached to a triangular black steel frame with a wooden handle on one side were two mirrors, several dark shades, a small telescope and an index arm with a micrometer drum that swung along a silvered arc marked in degrees. Colin showed me how to hold it, with the handle in my right hand and my eye to the telescope.

I had to measure the height of the sun above the horizon just as it reached its highest point in the sky due south of us – as it crossed our meridian. Colin first adjusted the shades on the sextant, then, looking through the telescope, moved the index arm until the sun’s lower edge (or ‘limb’, in astronomical jargon) was more or less on the horizon. I then took his place in the main hatch, braced against the slow roll of the boat, and, gripping the handle firmly, peered tentatively through the telescope at the southern horizon.

Fig 1: Principles of the Meridian Altitude

All I could see at first was a circle divided vertically between a light half and a dark: the left-hand side was the direct view through the plain glass side of the horizon mirror, and the darker right-hand side was the reflected view of the sky above us through the heavily shaded index mirror. Then I found the horizon and, scanning to left and right, caught a glimpse of a brilliant white disc floating just above the dark line of the sea. In a moment it had gone, but then I caught and held it, fascinated to see it moving steadily upwards, the gap between the disc and the horizon widening all the time. It was the sun and I was watching the earth turn.

Fig 2: Diagram illustrating the sun’s varying declination. (G.P. is the geographical position: see Glossary (#ubc99ec1b-d650-5737-95ff-f4f58f3e6cf7).)

If I rocked the sextant from side to side, the sun swung in an arc across the sky. By adjusting the micrometer, I brought the disc slowly down until, when the sextant was held vertically, its lower limb was just kissing the horizon. The sun was still moving upwards, but much more slowly now as it neared our meridian. After a minute or two, the white disc paused at the top of its arc. Taking the sextant away from my eye, I looked at the scale and read off the angle: 64° on the main scale and 41 (60 minutes to one degree) on the micrometer. This was the sun’s meridian altitude, or ‘mer alt’.

Colin took the sacred instrument from me and confirmed the reading. I looked up the sun’s declination in the Nautical Almanac and made a few corrections to the observed angle. In a few minutes, to my astonished delight, I completed the simple addition and subtraction sums that yielded our latitude.

We were somewhere on the parallel of 43° 17' North, and – as Colin observed – I was now as well equipped to find my way safely across an ocean as any European mariner before the time of Captain Cook.