Cuando el naufragio del barco Endurance de Ernest Shackleton se encontró a casi 10,000 pies debajo de la superficie del mar de Weddell en la Antártida en marzo de 2022, estaba ubicado a solo 4 millas de su última posición conocida, según lo registrado por el capitán y navegante del Endurance, Frank Worsley, en noviembre. 1915.

Ese es un grado asombroso de precisión para una posición determinada con herramientas mecánicas, tablas de números de referencia del tamaño de un libro, lápiz y papel.

La expedición que buscaba el barco había estado buscando en un área submarina de 150 millas cuadradas, un círculo de 14 millas de ancho. Nadie sabía qué tan preciso había sido el cálculo de la posición de Worsley, o qué tan lejos podría haber viajado el barco mientras se hundía.

Pero como historiador de la exploración antártica, no me sorprendió descubrir cuán preciso era Worsley, y me imagino que quienes buscaban los restos del naufragio tampoco.

La navegación fue clave

El Endurance había salido de Inglaterra en agosto de 1914, con el irlandés Shackleton esperando convertirse en el primero en cruzar el continente antártico de un lado al otro.

Pero ni siquiera aterrizaron en la Antártida. El barco quedó atascado en el hielo marino en el mar de Weddell en enero de 1915, lo que obligó a los hombres a abandonar el barco en tiendas de campaña instaladas en el océano helado cercano. La fuerza del hielo aplastó lentamente al Endurance, lo hundió 10 meses después y dio inicio a lo que se convertiría en una increíble, y casi increíble, saga de supervivencia y navegación de Shackleton y su tripulación.

El propio liderazgo de Shackleton se ha convertido en materia de leyenda, al igual que su compromiso de garantizar que no se perdiera un solo hombre del grupo bajo su mando, aunque tres miembros del grupo de 10 hombres de la expedición en el Mar de Ross perecieron.

Menos conocida es la importancia de las habilidades de navegación de Worsley, un neozelandés de 42 años que pasó décadas en la Marina Mercante británica y la Reserva de la Marina Real. Sin él, la historia de la supervivencia de Shackleton probablemente habría sido muy diferente.

Marcando el tiempo

La navegación requiere determinar la ubicación de un barco en latitud y longitud. La latitud es fácil de encontrar desde el ángulo del Sol sobre el horizonte al mediodía.

La longitud requería comparar el mediodía local, el momento en que el Sol estaba en su punto más alto, con la hora real en otro lugar donde ya se conocía la longitud. La clave era asegurarse de que la medición del tiempo para esa otra ubicación fuera precisa.

Hacer estas observaciones astronómicas y hacer los cálculos resultantes fue bastante difícil en tierra. En el océano, con pocos puntos terrestres fijos visibles, en medio del mal tiempo, era casi imposible.

Así que la navegación dependía en gran medida de la "navegación a estima". Este fue el proceso de calcular la posición de un barco utilizando una posición previamente determinada e incorporando estimaciones de qué tan rápido y en qué dirección se movía el barco. Worsley lo llamó "el cálculo de rumbos y distancias del marinero".

Apuntando a tierra

When the Endurance was crushed, the crew had to get themselves to safety, or die on an ice floe adrift somewhere in the Southern Ocean. In April 1916, six months after the Endurance sank, the sea ice on which they had camped began to break up. The 28 men and their remaining gear and supplies loaded into three lifeboats—the James Caird, Dudley Docker and Stancomb Wills—each named for major donors to the expedition.

Worsley was in charge of getting them to land. As the journey began, Shackleton "saw Worsley, as navigating officer, balancing himself on the gunwale of the Dudley Docker with his arm around the mast, ready to snap the sun. He got his observation and we waited eagerly while he worked out the sight."

To do that, he compared his measurement with the time on his chronometer and written tables of calculations.

And so began one of the most remarkable rescue missions in history. In a small open lifeboat, six men sailed 800 miles across some of the roughest seas on the planet to get help. We think they navigated with these instruments, on display in #PolarWorlds pic.twitter.com/4lxgzfR1BL

— Dr. Claire Warrior (@ClaireWarrior1) March 9, 2022

A last hope of survival

Once they managed to arrive on a little rocky strip called Elephant Island, off the coast of the Antarctic Peninsula, they still faced starvation. Shackleton believed that the only hope of survival lay in fetching help from elsewhere.

Worsley was ready. Before the Endurance was crushed, he had "worked out the courses and distances from the South Orkneys to South Georgia, the Falklands and Cape Horn, respectively, and from Elephant Island to the same places," he recalled in his memoir.

The men used parts of the other lifeboats to reinforce the James Caird for a long sea journey. Every day, Worsley "watched closely for the sun or stars to appear, to correct my chronometer, on the accuracy of which our lives and the success of the journey would depend."

On April 24, 1916, Worsley got "The first sunny day with a clear enough horizon to get a sight for rating my chronometer." That same day, he, Shackleton and four other men set off under sail in the 22.5-foot James Caird, carrying Worsley's chronometer, navigational books and two sextants, used for fixing the position of the Sun and stars.

The boat journey

These men, in this tiny boat, were going from one pinpoint of rock in the Southern Ocean to another, facing high winds, massive currents and choppy waters that could push them wildly astray or even sink them. The success of this voyage depended on Worsley's absolute accuracy, based on observations and estimations he made in the worst possible environmental conditions, while sleep-deprived and frostbitten.

They spent 16 days of "supreme strife amid heaving waters," as the boat sailed through some of the most dangerous sea conditions in the world, experiencing "mountainous" swells, rain, snow, sleet and hail. During that time, Worsley was able to get just four solid fixes on the boat's position. The rest was "a merry jest of guesswork" to determine where the wind and waves had taken them, and adjusting the steering accordingly.

The stakes were enormous—if he missed South Georgia, the next land was South Africa, 3,000 miles farther across more open ocean.

As Worsley wrote later:"Navigation is an art, but words fail to give my efforts a correct name. … Once, perhaps twice, a week the sun smiled a sudden wintry flicker, through storm-torn cloud. If ready for it, and smart, I caught it. The procedure was:I peered out from our burrow—precious sextant cuddled under my chest to prevent seas from falling on it. Sir Ernest stood by under the canvas with chronometer, pencil, and book. I shouted "Stand by," and knelt on the thwart—two men holding me up on either side. I brought the sun down to where the horizon ought to be and as the boat leaped frantically upward on the crest of a wave, snapped a good guess at the altitude and yelled "Stop." Sir Ernest took the time and I worked out the result. Then the fun started! Our fingers were so cold that he had to interpret his wobbly figures—my own so illegible that I had to recognize them by feats of memory."

On May 8, they saw floating seaweed and birds, and then spotted land. But they had arrived at South Georgia amid a hurricane, and for two days had to fight being driven by wind onto an island they had spent weeks desperately trying to reach.

Finally, they came ashore. Three of the six men, including Worsley, hiked across unmapped mountains and glaciers to reach a small settlement. Worsley joined a rescue boat back to get the other three. Shackleton later arranged a ship to collect the rest of the men from Elephant Island, all of whom had survived their own unimaginable hardships.

But the key to all of it, and indeed the recent discovery of the Endurance's wreck, was how Worsley had fought desperate conditions and still repeatedly managed to figure out where they were, where they were going and how to get there.