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What is Dead Reckoning?

written by: Raunekk • edited by: Lamar Stonecypher • updated: 12/30/2009

Dead reckoning is an ancient navigational technique which helps a sailor to determine the current position of the ship on the basis of its past courses and speeds. Learn more about the dead reckoning navigational method in the article inside.

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    Introduction

    Dead reckoning is an ancient navigation technique which was used to find the direction and distance traveled by a ship. Dead reckoning is one of the oldest navigational techniques, which still has an influence on the present day navigational systems. The method facilitates the sailor to determine its current position on the basis of the paths and speeds already traveled by the ship. Moreover, dead reckoning also allows the sailor to plan his future courses along with the required speed.

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    Understanding Dead Reckoning

    Though Dead reckoning is the navigational method of the past, many modern navigation systems are based on the same principle. In fact, dead reckoning is supposed to be the first method in the history of marine navigation that required keeping a daily log.

    In the early days of using dead reckoning, the sailor used to measure the position and distance traveled by the ship from a fixed position or point, for e.g., the port from where the ship started. The sailor accordingly used to make a chart, marking the points with pins. The points would represent the course and direction traveled along with the speed. For measuring the direction magnetic compass were used, whereas speeds were measured by using chip log or other similar methods. Along with the chart, all the details were also recorded in a report log, which was updated every hour or within regular interval of time.

    Measuring a ship’s speed involved throwing a wooden log in the sea water just ahead of the ship's forward. The ship was marked with a sign both on the forward and aft side. The sailor would make a note when the wooden log passed the forward and aft mark. Then using the time required by the log to pass between the two marks and some conversion techniques the exact speed of the ship was found. These measurements were carried out every hour and were noted down on the chart and log book. A track of the course and speed was taken with the help of equipment known as transverse board.

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    Modern Application

    Coming to the modern age, dead reckoning has been the reason behind many of the modern navigation equipments. As the working principle of the modern charts is the same, contemporary methods are used to measure the various parameters needed. Pit log is one of the famous methods, which is used for measuring the speed of the ship. The device used for this purpose is known as pit sword or rod meter. The measurements are taken at predetermined intervals and the duration between the intervals varies according to the requirement. In modern applications also, the port or any known fixed point is taken as the reference point. If a known point is not available then any estimated point is considered as the reference point.

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    Additional Information

    It is to note that dead reckoning is just an approximation and thus not count factors such as current and wind speed while calculating the parameters. Moreover, dead reckoning also allows predicting sunset and sunrise and various other natural phenomena.

    Though currently, GPS has taken over all methods and is considered the most accurate and easy way for navigation, it might become unreliable in case of network or equipment failure. In such cases a habit of keeping a dead reckoning log might be extremely beneficial.

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