She struck at about half past eight in the evening, at high water, running for Sydney with 117 people aboard. The obstruction was a reef the charts called Las Roccas — today the Rocas Atoll, the only atoll in the South Atlantic — a ring of coral and red algae some 260 kilometres off the Brazilian coast whose highest point is a six-metre sand dune. In October 1865 nothing marked it; no lighthouse would be built there for another sixty-eight years. What happened over the ten days that followed is the reason anyone still remembers the Duncan Dunbar. Everybody lived.
She went down the ways on 18 May 1857 from James Laing's yard at Sunderland, the twelfth ship Laing had built for Duncan Dunbar & Company and, at that moment, the largest vessel ever launched on the River Wear. A crowd turned out for it, and Mrs W. R. Robinson of Silksworth did the christening. She was wood throughout — English oak frames, East India teak for planking and masts — fastened with copper bolts and braced with iron trusses and knees: 260 feet overall, 229 feet 2 inches at the keel, a beam of 36 feet 3 inches, a hold 23 feet deep, 1,447 tons register against a burthen of 2,500. The name honoured a Duncan Dunbar, though sources differ on which one, since the firm's owner and his father shared it. She spent her working life on the England–Australia run, carrying passengers and freight. When Dunbar died in 1862 she passed to Gellatly, Hankey, Sewell & Co.
She left London on 28 August 1865 and cleared Plymouth on 2 September, bound for Sydney under Captain Swanson. Five weeks out, in darkness, she came onto the reef. Rocas is a difficult thing to see and an easy thing to hit: an oval barely 3.7 kilometres by 2.5, ringed by coral that breaks only at low water, with a shallow lagoon inside and two small sand cays — Farol and Cemitério — that between them amount to a third of a square kilometre of dry land. Everyone got off the ship and onto the coral. Then they moved to the cay that stood about seven feet above ordinary high-water mark, which was as much elevation as the South Atlantic had to offer them.
For the first two days each person had a pint of water a day. The temperature on the sand was recorded at 112 °F — 44 °C. There was no shade worth the name, no fresh water, and no reason to think anyone ashore knew where they were. A hundred and seventeen people, among them the passengers who had paid for a berth to Australia, waited on a bar of sand seven feet above the tide and watched the horizon. They stayed there ten days.
On 11 October, four days after the wreck, Captain Swanson put out in a lifeboat and set a course for Pernambuco on the Brazilian mainland. He had covered about 120 miles when the American ship Hayara picked him up. Word travelled from there, and the Royal Mail Steam Packet Company's steamer Oneida turned for the atoll, came in to the island and took every one of them off. They were landed at Southampton. The accounts record no loss of life: 117 people onto the coral, 117 people home.
There is a coda, and it is a grim one. Eight years earlier a different ship, simply the Dunbar, had been driven onto the cliffs of South Head at the entrance to Sydney Harbour on 20 August 1857. Of the 122 aboard — 59 crew and 63 passengers — 121 died. One able seaman, James Johnson, clung to the rock face until he was found. Mark Twain described that disaster in Following the Equator and, in the telling, called the ship the Duncan Dunbar, permanently muddling the vessel that killed almost everyone with the vessel that saved everyone. Rocas Atoll itself is now a Brazilian biological reserve open only to researchers, and has been a UNESCO World Heritage Site since 2001. A derelict lighthouse from 1933 and a working Navy light stand on Farol Cay, on the sand where the survivors waited.
Rocas Atoll lies at 3.867°S, 33.750°W, roughly 260 km northeast of Natal and 145 km west of Fernando de Noronha. From 3,000–6,000 ft the whole oval reads clearly — a bright turquoise lagoon inside a near-continuous ring of surf, with the two pale sand cays on the western side. The lighthouse on Farol Cay is the only structure. Nearest fields are Fernando de Noronha (SBFN), about 145 km east, and Natal / Governador Aluizio Alves International (SBSG) on the mainland. The reserve is closed to landing and low overflight should be avoided; seabird activity is heavy. Light is best mid-morning, when the sun angle brings out the lagoon colour.