If you’re armed with a solid data connection and a recently-charged phone battery, it can be quite difficult to get lost these days. Whether you’re looking for your hotel, a local restaurant, or a tourist spot of interest, a service like Google Maps or Apple Maps will usually quickly point you in the right direction. We’re spoiled for choice when it comes to convenient ways to plan a trip or course-correct on the fly if things go awry, but it hasn’t always been that way. Far from it, in fact. Lots of today’s ships have the luxury of advanced GPS systems. When everything’s working properly, there are no surprises along the way as — for instance — a cruise ship follows its itinerary. It really makes you feel for seafaring pioneers like the Vikings and other historical figures like Ferdinand Magellan and Sir Francis Drake, who each led expeditions around the world in the 1500s.

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GPS technology wasn’t introduced until the mid-to-late twentieth century. Prior to this, a very different range of natural and human-made tools were used by sailors to determine their position and plot a course at sea. Lancaster University quotes physicist Dr Joe Kinrade as noting, “From about the 16th century, the world was opening up to exploration and trade … Ocean navigation shifted from the realm of astrology and ‘dead reckoning’ to astronomy and trigonometry.” A wide range of complicated and brilliant methods have been used by sailors, and some of them continue to be employed today alongside GPS technology. It was challenging enough at the time for surface ships, so try and imagine how early submarines navigated the depths.

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Nature can confound navigators with thick fog and other unfriendly weather conditions when it chooses, but the open ocean typically offers wonderful starry vistas. Sailors aren’t just interested in the stunning view, though; celestial navigation is a crucial tool, both before technological developments were made and now in tandem with them. One of the keys to doing so is the North Star. This bright and beautiful body faithfully points the way to the north pole, acting as something of a natural sky-mounted compass. Along with the sun, it can also be used to determine the ship’s latitude through a measurement of its height in the sky relative to the horizon. In shallow waters, sailors often compared depth measurements to charts to pinpoint their location. On the open sea they used a technique known as “dead reckoning,” where the ship’s known direction of travel was plotted over time on navigational charts, and objects were observed as they floated past the ship to make adjustments for current and wind.

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The longitude of a ship was far more difficult to determine than its latitude, though. As a result, vessels learned to use a technique that involved plotting a course further to the east or west of their intended destination, then traveling back along their latitude to find it. Another technique was coastal navigation. The concept is an obvious one: Sophisticated instruments aren’t needed if you stay close enough to land that you can still see exactly where you are from the landmarks of the region. Well-traveled routes, of course, would offer islands, cliffs, mountains, lighthouses, and other prominent features that veteran sailors became familiar with.

Human ingenuity, of course, led to our development of a range of instruments to be used on ships for navigation. One of the most important of these is the sextant, which goes back centuries. Philadelphia’s Thomas Godfrey introduced the double reflecting sextant in 1730.  This instrument boasts two mirrors and an arm that can be positioned along a scale. This allows the user to accurately measure the angle between two visible objects, like the North Star and horizon.

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Another crucial tool for ocean navigation was the backstaff. These typically wood-and-brass devices were positioned so that they provided the Sun’s height in the sky on the scale of the device. Both of these instruments, then, can be used to determine latitude, a crucial aspect of navigation. On ships, compasses have often been built into a binnacle, a mounting post near the ship’s helm. They did require some calibration, though, just as iPhone compasses do today. The introduction of the hourglass, meanwhile, was a huge boon for the timing that was central to accurate dead reckoning navigation.

Charts were not simple maps of an area, but — much like the paper road maps that motorists relied on before the introduction of GPS — were comprehensive guides dedicated to that form of transport. They provided information on port locations and tricky-to-navigate areas of waterways such as reefs and shoals,  although in centuries past some of their makers took creative liberties or repeated others’ inaccuracies. Charts were often used in conjunction with other instruments, and they still are.

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The classic methods haven’t become entirely obsolete. Modern technology can be fickle, and when any issues arise, it is often the electricity-free methods that users fall back on. As Dr Kinrade explained, “most ships still carry a sextant as a backup to modern satellite-based navigation systems.” Modern technology is far from infallible, and the pioneers of the sextant would surely be gratified to know that their instrument is still playing a pivotal role in navigation centuries later. The humble compass is another a common piece of gear that is still brought along on ocean voyages. Sailors are trained in the used of these tried-and-true low-tech tools in case any of their sophisticated instruments should fail in an inhospitable and lonely section of the ocean. It’s important that electronic and manual methods of navigation are used in tandem, as it’s easy for shipping accidents to occur.

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One such prominent case was that of the Leda Maersk, a container ship from Denmark that ran aground in New Zealand in June 2018. The Transport Accident Investigation Commission‘s comprehensive report into the incident determined that “neither the harbour pilot nor the ship’s bridge team recognised that the Leda Maersk was deviating from the planned track. This was because they were not fully using the electronic navigation aids.” The report continued, “the entire bridge team was primarily navigating ‘by eye.'”  Of course, knowledgeable nautical navigators can journey in such a fashion. The U.S. Navy website quotes 1st Lieutenant Tyler Gehr as noting that doing so serves as “a reminder that despite all of the high-tech tools we have on the bridge, we should not overlook the stellar skills of our Sailors.”

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