How Did the Sinking of a Ship in 1707 Lead to the Invention of the Marine Chronometer?

2014 marked the 300th anniversary of the passing of the Longitude Act. It is also the year when the remains of the British second rate ship of the line, Association, were officially protected. The reason why the shipwreck changed the course of maritime history can be traced to a single navigational error, made one stormy night in 1707.

The perils of dead reckoning

Early sea navigators could find accurate latitude - their ship's position north or south of the equator - by observing the sun. Longitude - an east-to-west measurement - was calculated by estimations of speed and course from a given position at a given time, known as 'dead reckoning'. This method risked cumulative error, compounded by variables of wind, current and tide and the impossibility of keeping accurate time at sea, where motion and temperature could affect timepieces.

The possibility of miscalculating longitude at sea was a serious problem in an era that saw the expansion of both the Royal Navy and the mercantile marine. All too often, ship after ship - unaware of their exact location - made unexpected landfall on rocks and sandbanks and were wrecked. The British government realised that it was crucial to stop this high toll in ships and men, and a night in October 1707 was the final catalyst for action.

On 21 October a fleet of 21 ships, homeward-bound from the Mediterranean, entered the English Channel in stormy weather, led by their flagship Association, under Sir Cloudesley Shovell. Shovell conferred with his fleet about where they were longitudinally, and it was agreed that they had reached the French island of Ushant, off Brittany. In fact, they were much further north, near the Isles of Scilly, which mark the northern Channel approaches.

The following night, Association smashed into rocks west of Scilly, followed by the Eagle, Romney and Firebrand. All four - with over 2,000 men - were lost, and only 25 mariners survived.

The Scilly Naval Disaster: catalyst for change

The Scilly Naval Disaster provided the trigger for the Board of Longitude's quest to determine longitude at sea. The result was the Longitude Act 1714, which offered a reward of £20,000 to the first person to discover a reliable means of determining that measurement.

In reality, it took years to find a solution to the problem. It was clockmaker John Harrison's marine chronometer that provided the answer, but he was only awarded £8,750 in 1773 for his timekeeper (neither he nor anyone else ever obtained the full prize money).

Yet there is an aspect of Harrison's dedicated work that provides an enduring legacy. Determining accurate coordinates not only helps to prevent shipwrecks, it also provides a means by which shipwreck sites can be located, recorded and, ultimately, designated as heritage assets.

300 years on…

The remains of Association, which still lie scattered among the rocks off the Isles of Scilly, were recently designated under the Protection of Wrecks Act 1973, for their seminal archaeological importance. Before the wreck was protected, a large number of gold and silver coins were recovered and sold at auction, including ones from France, Belgium, the Netherlands and Spanish America, along with English coins from the reigns of Charles I, Charles II, James II and William III.

What remains on the seabed are iron cannon, cannon balls, anchors and smaller artefacts spread around the rocky gullies.

Find out more about how maritime remains are preserved.

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