1707 - Fleet Shipwreck

On the 22nd of October, three ships of the line, the 90-gun Association, the 70-gun Eagle, and the 50-gun Romney run aground on the Western reefs of Scilly islands. They founder with all hands but one. The fireship Firebrand also goes ashore and sinks with half her crew. The 90-gun St George and the fireship Phoenix strike on the reefs too but manage to get off. On her own, the 100-gun Royal Anne escapes the rocks within a hair. A thousand and three hundreds sailors drown.

Those ships belong to Admiral Cloudesley Shovell’s fleet. Shovell, 57 years old, is a highly distinguished officer endowed with splendid record of serving at the battles of Barfleur (1693), Gibraltar (1702), Malaga (1704) and Barcelona (1705).

On the way from Gibraltar to Portsmouth, returning from a campaign in the Mediterranean sea, Shovell’s fleet has encountered bad weather all journey long. They nevertheless achieved to make a position, through the usual Davis’ backstaff, at noon on the 21st of October which located them at 200 miles West-Southwest of the Scilly islands. Their latitude is supposed1 to be 48°50’ which is one degree South of the 49°53’ of Bishop Rock, the most Western Scilly islet at 4 miles off St Agnes island. The ships also sound the seabed to assess longitude, which seems to be confirmed. The fleet headed then East-by-North, which sounded comfortable to evade the reefs based on flagship’s measured latitude – which remains unknown to us but was most likely erroneous.

¤ We say ‘supposed’ latitude for it was measured on a surviving ship but other surviving logs gave a range of latitudes spread over 25 minutes. The 80-gun Torbay’s captain noted in his log that they might be Northward from the supposed position.

¤ The Davis' Backstaff is not an accurate instrument. Handled with skill and much care, it meters altitude with some 15' accuracy. Add rolling & pitching, remove skill, and we get 30 or 45'.

The Scilly islands are especially dangerous, being the place of twenty previous shipwrecks recorded. In 1680, a coal-burning lighthouse was therefore set on St Agnes island, despite the objection from the Governor of the Scilly’s who feared to loose the revenue of plundering wrecks...

In 1700, Edmund Halley, the famous astronomer who also produced data crucial to navigation as everybody knows, published ‘An Advertisement Necessary to All Navigators Bound up the Channel of England’ : he reminded the reader of the existence of a magnetic deviation of 7° West which may mislead them to North and warned of a mistake in pilot books which place the islands fifteen miles North off their real position ; thus he prescribed to keep below a latitude of 49°40’, a precaution that seems to be theoretically taken by Shovell.

At the last minute before the shipwreck, several sailors aboard a few ships have seen the glow of the lighthouse three miles away and the dim light of the waves shattering on the reefs nearby. It ultimately saves the St George and the Royal Anne. We can see the benefit of setting lighthouses.

An error of longitude is widely incriminated for the shipwreck. It seems not to be the case but it paves the way to tackling the difficult question of measuring longitude. Actually, the disaster likely stems from a cumulation of uncertainties on latitude, on read course and on real one owing to compass variation and a to drift bearing to North, and on real positions of the rocks against their locations on the charts.

¤ Longitude was not that uncertain in so much as soundings ascertained a position on the edge of the continental shelf on the 21st of October – a usual way of readjust position which has been carefully performed by Shovell.

¤ Four in 112 compasses on surviving ships will be considered as serviceable according to the variation control performed afterwards.

It demonstrates : (1) inaccuracy of the Davis’ backstaff on a rolling & pitching ship ; (2) loss of accuracy of compass with time spent aboard which may induce a difference of one or two points on the course ; (3) existence of mistaken charts, even on Royal warships, which place the islands northward of their real position ; (4) ignorance of possible currents but the main coastal ones ; (5) usual underestimation of drift causes ; (6) usual mistake of not sharing data and of not confronting navigation discrepancies within a fleet.

¤ Such a deviation of one or two points may be responsible for a drift in latitude by 10 or 20’ over the 200-mile course. A half-a-knot drift to North may be considered as likely in this case.

¤ Backstaff refers to an instrument meant to measuring altitude of the sun by its shadow when you set it at your back. The device is not depicted in its position of shooting. Let us imagine the operator on the right of the picture, lifting the cumbersome device. He has set the sun at his back and approximately positioned the shadow vane on the top of the small arc so as to see sun shadow falls on the slit on the left. He then adjusts the sight vane to displace horizon in coincidence. The altitude is the sum of the two arcs.

The later fault is accountable to Shovell. The procedure weaknesses, the material deficiencies and the map defaults are attributable to the Admiralty, which cynically lets the public believe and chatter about the longitude issue as the cause of the disaster.

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SUGGESTED BIBLIOGRAPHY

Anonymous (Abel Boyer) – The Annals of Queen Anne’s Reign for 1707 – London - available on the Internet

W. E. May – The Last Voyage of Sir Clowdisley Showel in Journal of Navigation – London, 1960

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CREDIT

Michael Dahl's studio – portrait of Cloudesley Shovell - oil on canvas, 1702 - © National Portrait Gallery

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