They lived in the cramped hold, crawling in and out through a small hatch to take watches. Hot meals came every four hours from a small Primus stove that was their only source of warmth. Water froze in the containers; they melted ice for drinking and cooked with seawater when fresh water ran short. The sleeping bags became saturated with salt water and provided almost no insulation. Sleep was possible only in the intervals between swamping.
Worsley’s navigation was the factor on which everything else depended. He had a sextant, a chronometer, and the accumulated knowledge of a lifetime at sea. He had almost no opportunities to use them. In the 16 days of the crossing, he managed to take only four sun sights: on April 26 and May 3, 4, and 7. The rest of the voyage was dead reckoning — his own best calculation of where the boat was based on speed, direction, and elapsed time, what he called, with the black humor appropriate to the situation, “a merry jest of guesswork.”
The mechanics of taking a sun sight from the James Caird required two men. To lean far enough out of the boat to bring the sun to the horizon through the sextant, Worsley had to hang over the side with his chest on the rail. Someone had to hold the chronometer and read off the seconds, because Worsley’s hands were occupied with the instrument. Shackleton held the chronometer. Worsley’s fingers were too numb from cold to read his own figures, and Shackleton had to read them from his hands.