SEA HISTORY for kids In October of 1707, leading a British fleet of 21 ships home from duty in the Mediterranean Sea, a high-ranking and experienced admiral-Sir Cloudesley Shovell- steered his ship directly onto the rocks off the Isles of Scilly, 28 miles west of England in the Atlantic Ocean. Following close astern, three more ships smashed up on the rocks and were wrecked before they could change course and get into deeper water. All told, nearly 2,000 men died that day, making it the worst naval disaster in British history. How could Admiral Shovell, who at that point had been in the navy for 43 years, have made such a grievous navigational error ? The captains on the surviving ships reported that the fleet had been sailing through very bad
Not being able to get a fix on the nautical chart led many a ship to its doom. weather and could not get an accurate fix , or location, on the nautical chart fo r some time. In those days, mariners determined their location at sea by keeping track of their course direction and speed, called dead reckoning, and by taking measurements of the sun, stars, moon , and planets relative to their position on earth . There was considerable guesswork involved, as navigational tools were not all that accurate. The basic tools available in that era were the magnetic compass, nautical charts, a quadrant or backstaff, and t he leadline. If any of these items lacked in accuracy, then the mariner using them could only estimate his pos ition at sea. Shovell's fleet captains testified that they had been unable Sir Cloudesley Shovel! was a serious and to determine their position on the chart for several days and that they assumed experienced navigator, but the limita- they were much fu r ther south than they really were. When the admiral had the tions of his tools kept him from being fleet turn east, thinking he was heading into the Eng lish Channel, instead they turned right into the tiny but jagged and rocky Scilly Islands. able to keep his ship offthe rocks. Let's take a look at two of the basic tools sailors used then that they still use today: the nautical chart and the lead line.
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CHART AND GLOBE IMAGES Ai'lD I N FORMATIO N COURTESY NOAA OFF ICE O F COAST SU RVEY
The nautical chart is a type of map, which has unique characteristics and a detailed representation of the coastline. It includes lots of information about local tide ranges and geographical features that are critical to the navigator. Unlike regular maps that include details about the land and only blue space where there is water, the nautical chart only includes landmarks and features ashore if they might be easy to recognize from seaward, such as a tall building or tower. Most of the details ar e in the water, such as depth (or soundings), seafloor characteristics (is it muddy, sandy, rocky?), aids to navigation (buoys and lighthouses), and local information that might be relevant, such as strong currents, protected areas, anchorages, shipping lanes, etc. All those numbers in th1e water (blue and white areas) on this chart note the wateer depth in either fathoms or feet. A fathom is 6 feet and iis used to label deeper water.