William E. Carter and Merri Sue Carter in American Scientist:
Travel by sea was slow and dangerous during the age of sail. Many ships intending to carry cargo or passengers to distant ports, to wage war or to discover new lands, met disaster at sea and were never heard from again. It was not at all uncommon for coastal vessels simply transporting goods from port to port along the rugged British coastlines to get caught up in fast-moving storms and be driven ashore, at the cost of cargo, ships and lives. But it was extraordinary when, in 1707, a fleet of British naval vessels under the command of Admiral Sir Cloudesley Shovell sailed headlong into the Isles of Scilly off the coast of Cornwall. Having the bodies of hundreds of British seamen, including members of some of the nation’s leading families, wash up on homeland beaches was simply unacceptable. People demanded that an effort be made to prevent such a tragedy from occurring again.
Shovell and his fleet had sailed from Gibraltar bound for England on or about October 10, 1707. They suffered stormy weather nearly continuously for the next 10 days. They were unable to make reliable astronomic observations and were forced to navigate by dead reckoning, a process that combined compass readings and speed estimates. On October 21, soundings found the water depth to be some 90 fathoms, suggesting that the fleet was nearing land, and the skies cleared enough to permit some astronomic observations. The results were inconsistent but seemed to indicate that the fleet was just offshore of Ushant, France. If that was the case, sailing northeast would carry the fleet safely into the English Channel and Admiral Shovell issued orders to do just that.