Marine Navigational Equipment: The Sextant

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Is the sextant a carthorse in the 21st century?

The purpose of this report is to decide whether the sextant is outdated and effectively useless in the modern age or whether it still has a use in modern navigation. To decide this I explored modern navigation techniques, which is mostly done by global positioning systems, I researched the way that these work and the methodology behind the use of a sextant. The conclusion that I came to was that modern day sextant use is rare unless practicing for an emergency. Since its release GPS has dominated and is now the main source of navigation on most vessels (big or small). The reason for this dominance is the reliability and effectiveness of the GPS system. So unless there is a major problem it leaves the sextant as a practically useless device aboard a ship. This means that fewer people are learning how to use a sextant and are carrying spare GPS as a backup device rather than the sextant. However the sextant has been used for centuries as it is a reliable device but takes skill and knowledge to use which is dying out of modern sailing.


There are many different ways of navigating whilst at sea most of them involve taking a bearing from a landmark that you can see and then plotting that bearing on a chart and triangulating your position using landmarks. However this becomes hard when you are out in open water and cannot see any noticeable landmarks. This then requires another method of positioning such as a sextant or GPS system. The sextant has been used for century's and is one of the oldest and most reliable forms of navigation. This essay is about the differences and modern day relevance that the sextant has on current navigation techniques.

The sextant
The sextant was developed in 1760 by a man called John Hadley (Ifland 1998). He first developed a device that he called the Octant that is the basic design of the sextant. Until this point sailors had used several similar devices to determine the latitude of the vessel but determining longitude was much harder. This was due to it being necessary for the individual to know the exact time. Until a method of precise timekeeping was developed it was very hard for navigators to work out the longitude of the vessel causing many shipwrecks. They developed a technique that allowed them to work out the time by measuring the angle between the moon and a celestial body. The problem with this technique is that it was not particularly accurate causing there to be many mistakes. In 1759 John Bird built the first working sextant by making the original octant bigger allowing it to take reading up to 120 degrees rather than the octants 80 (Ifland 1998). This allowed for more accurate measurements to be taken of celestial and lunar observations. Sextants work by measuring the angle between any two objects that are visible. By measuring the angle between the sun and the horizon you can determine the latitude based on the time of day.

Brighthub Engineering. (2013)

"The optical principle used in a sextant is this: given that a ray of light is reflected from two mirrors in succession, then the angle between the first and last direction of the ray is twice the angle between the mirrors. (Manu 2013) " The time and the angle of when the object was measured are used to gain a position line on a chart. The sun is mainly used as a celestial object with the readings being taken at solar noon. There are several different terms for taking the measurement these include sighting/ shooting the object and taking a sight. The other main celestial object that is used is Polaris (the North Star) with the reading being taken at night. These readings along with a series of calculations allow the user to work out the latitude of ones vessel.

Global positioning system (GPS)

GPS is a modern system that is used as a navigation guide this system is more commonly considered a help to navigating rather than a...
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