Many shipwrecks have occurred when the crew of the ship allowed the ship to collide with rocks , reefs , icebergs , or other ships . Collision has been one of the major causes of shipwreck . Accurate navigation is made more difficult by poor visibility in bad weather . Also , many losses happened before modern navigation aids such as GPS , radar and sonar were available . Until the 20th century , the most sophisticated navigational tools and techniques available - dead reckoning using the magnetic compass , marine chronometer ( to calculate longitude ) and ships logbook ( which recorded the vessel 's heading and the speed measured by log ) or celestial navigation using marine chronometer and sextant - were sufficiently accurate for journeys across oceans , but these techniques ( and in many cases also the charts ) lacked the precision to avoid reefs close to shore . The Scilly naval disaster of 1707 , which claimed nearly 2,000 lives and was one of the greatest maritime disasters in the history of the British Isles , is attributed to the mariner 's inability to find their longitude . This led to the Longitude Act to improve the aids available for navigation . Marine chronometers were as revolutionary in the 19th century as GPS is today . However the cost of these instruments could be prohibitive , sometimes resulting in tragic consequences for ships that were still unable to determine their longitude , as in the case of the '' Arniston ''
Scilly naval disaster of 1707
Scilly naval disaster of 1707
Shipwrecking