There was much discussion of the difficulties facing mariners approaching the channel in the years both before and after the Scilly disaster.
In 1700, Edmond Halley published an "advertisement" (warning) concerning the dangers of ships mistakenly passing north of Scilly, rather than to the south, as intended, "not without great danger, and the loss of many of them".
He identified two factors, the failure to take account of magnetic variation, then about 7° west, and errors in the pilot books, placing the islands up to 15 miles north of their true position.
He recommended a course not more northerly than 49° 40' to stay safely to the south of both the Scillies and the Lizard.
Another possible factor, suspected by some mariners at the time, but not documented for nearly another 100 years was the existence of a north-setting current, Rennell's Current, that could run at 15 miles in 24 hours, quite sufficient to put a ship into danger.
The current builds up with strong westerly or south-westerly winds, as was the case in October 1707.

Writing about the Scilly disaster in 1720, Josiah Burchett wrote: "I cannot but have a lively idea of the danger fleets are exposed to upon entering the British Channel, when coming from foreign parts, but more especially when their officers have not the advantage of knowing their latitude by a good observation".
 Thus both these writers identified the importance of errors in latitude.

Longitude was also, obviously, important for a ship approaching the channel.
Before astronomical methods of determining longitude became available, navigators used soundings of the ocean depth with lead and line.
The continental shelf extends to about the 100 fathom line (180 m) then drops very sharply to thousands of metres.
A ship coming "into the soundings", where the depth could be measured with a 100-150 fathom sounding line thus knew its approximate longitude.

The information available to the fleet has been analysed using data from the numerous log books of the surviving ships.
It has sometimes been assumed that the bad weather on the voyage prevented the determination of latitude, but the weather cleared enough for some observations to be made.
Thus the positions calculated are a mixture of dead reckoning, soundings, and observations of latitude.
The approximate course of the fleet is shown at right, with positions shown for the last two days from the logs of ships that survived the disaster.
The chart also shows Halley's recommended northern limit.
They were clearly too far north to continue heading E by N. Again, this suggests an error in latitude.
May notes that while the latitudes recorded in the log-books was more accurate than the longitudes, there was still a spread of over 40 nautical miles in the recorded latitudes .

H.M.S. Orford, and Lieutenant Lochard's log, survived the disaster.
H.M.S. Association and her logs did not, so we have no way of knowing exactly what information Shovell had.
The account of a council of the ships' masters that discussed their position is almost certainly one of the myths of the disaster, as suggested above.
But if Shovell headed E by N towards the Channel at night-time, he presumably believed he was safely to the south of the Scillies.
The Captain of the Torbay wrote in his journal "We were much to ye Northward of what was expected, and likewise more to the Eastward".

While Dava Sobell's assertion that the disaster was mainly due to an error in longitude cannot be sustained, the disastrous wrecking of a Royal Navy fleet in home waters caused great consternation to the nation, and brought home the poor state of navigation.
The Royal Navy conducted a court-martial of the officers of the Firebrand, who were acquitted, but no officers survived from the other lost ships, so no other courts-martial took place.
The Navy also conducted a survey of compasses from the surviving ships and of those at Chatham and Portsmouth dockyards, following comments from Sir William Jumper, captain of the Lenox, that errors in the compasses had caused the navigational error.
This showed what
There was much discussion of the difficulties facing mariners approaching the channel in the years both before and after the Scilly disaster. In 1700, Edmond Halley published an "advertisement" (warning) concerning the dangers of ships mistakenly passing north of Scilly, rather than to the south, as intended, "not without great danger, and the loss of many of them". He identified two factors, the failure to take account of magnetic variation, then about 7° west, and errors in the pilot books, placing the islands up to 15 miles north of their true position. He recommended a course not more northerly than 49° 40' to stay safely to the south of both the Scillies and the Lizard. Another possible factor, suspected by some mariners at the time, but not documented for nearly another 100 years was the existence of a north-setting current, Rennell's Current, that could run at 15 miles in 24 hours, quite sufficient to put a ship into danger. The current builds up with strong westerly or south-westerly winds, as was the case in October 1707.
Writing about the Scilly disaster in 1720, Josiah Burchett wrote: "I cannot but have a lively idea of the danger fleets are exposed to upon entering the British Channel, when coming from foreign parts, but more especially when their officers have not the advantage of knowing their latitude by a good observation".  Thus both these writers identified the importance of errors in latitude.
Longitude was also, obviously, important for a ship approaching the channel. Before astronomical methods of determining longitude became available, navigators used soundings of the ocean depth with lead and line. The continental shelf extends to about the 100 fathom line (180 m) then drops very sharply to thousands of metres. A ship coming "into the soundings", where the depth could be measured with a 100-150 fathom sounding line thus knew its approximate longitude.
The information available to the fleet has been analysed using data from the numerous log books of the surviving ships. It has sometimes been assumed that the bad weather on the voyage prevented the determination of latitude, but the weather cleared enough for some observations to be made. Thus the positions calculated are a mixture of dead reckoning, soundings, and observations of latitude. The approximate course of the fleet is shown at right, with positions shown for the last two days from the logs of ships that survived the disaster. The chart also shows Halley's recommended northern limit. They were clearly too far north to continue heading E by N. Again, this suggests an error in latitude. May notes that while the latitudes recorded in the log-books was more accurate than the longitudes, there was still a spread of over 40 nautical miles in the recorded latitudes .
H.M.S. Orford, and Lieutenant Lochard's log, survived the disaster. H.M.S. Association and her logs did not, so we have no way of knowing exactly what information Shovell had. The account of a council of the ships' masters that discussed their position is almost certainly one of the myths of the disaster, as suggested above. But if Shovell headed E by N towards the Channel at night-time, he presumably believed he was safely to the south of the Scillies. The Captain of the Torbay wrote in his journal "We were much to ye Northward of what was expected, and likewise more to the Eastward".
While Dava Sobell's assertion that the disaster was mainly due to an error in longitude cannot be sustained, the disastrous wrecking of a Royal Navy fleet in home waters caused great consternation to the nation, and brought home the poor state of navigation. The Royal Navy conducted a court-martial of the officers of the Firebrand, who were acquitted, but no officers survived from the other lost ships, so no other courts-martial took place. The Navy also conducted a survey of compasses from the surviving ships and of those at Chatham and Portsmouth dockyards, following comments from Sir William Jumper, captain of the Lenox, that errors in the compasses had caused the navigational error. This showed what
Scilly naval disaster of 1707