page_title: Dead reckoning
section_title: Marine navigation
hierarchical_section_title: Dead reckoning / Marine navigation
caption_attribution_description: English: Basic Marine Navigation tools for Dead Reckoning from the Canadian Yachting Association Coastal Navigation course. The objects are photographed on top of a nautical training chart. The purple book is "Chart 1"; on top of Chart 1 is a navigator's notebook with a Dead Reckoning navigation plan at the top of the page. A dead reckoning navigator must be able to tell time, so he has a rugged watch. He needs a Tide Table in tidal waters so he can determine the effects of tidal currents on the vessel's progress. Dividers are used to meaure distance. A plotter is used to draw course lines, bearings, and fixes on the chart. The navigator's pencil is marked off in 10 nautical mile intervals, to make estimating and double-checking easy. The tip of the pencil points to an area on the chart with several DR course lines, bearings, and fixes plotted.
context_page_description: In navigation, dead reckoning is the process of calculating one's current position by using a previously determined position, or fix, by using estimations of speed and course over elapsed time. The corresponding term in biology, used to describe the processes by which animals update their estimates of position or heading, is path integration.
  Dead reckoning is subject to cumulative errors. Advances in navigational aids that give accurate information on position, in particular satellite navigation using the Global Positioning System, have made simple dead reckoning by humans obsolete for most purposes. However, inertial navigation systems, which provide very accurate directional information, use dead reckoning and are very widely applied.
context_section_description: In marine navigation a "dead" reckoning plot generally does not take into account the effect of currents or wind. Aboard ship a dead reckoning plot is considered important in evaluating position information and planning the movement of the vessel.
  Dead reckoning begins with a known position, or fix, which is then advanced, mathematically or directly on the chart, by means of recorded heading, speed, and time. Speed can be determined by many methods. Before modern instrumentation, it was determined aboard ship using a chip log. More modern methods include pit log referencing engine speed (e.g. in rpm) against a table of total displacement (for ships) or referencing one's indicated airspeed fed by the pressure from a pitot tube. This measurement is converted to an equivalent airspeed based upon known atmospheric conditions and measured errors in the indicated airspeed system. A naval vessel uses a device called a pit sword (rodmeter), which uses two sensors on a metal rod to measure the electromagnetic variance caused by the ship moving through water. This change is then converted to ship's speed. Distance is determined by multiplying the speed and the time. This initial position can  then be adjusted resulting in an estimated  position by taking into account the current (known as set and drift in marine navigation). If there is  no positional information available, a new dead reckoning plot may start from an estimated position. In this case subsequent dead reckoning positions will have taken into account estimated set and drift.
  Dead reckoning positions are calculated at predetermined intervals, and are maintained between fixes. The duration of the interval varies. Factors including one's speed made good and the nature of heading and other course changes, and the navigator's judgment determine when dead reckoning positions are calculated.
  Before the 18th-century development of the marine chronometer by John Harrison and the lunar distance method, dead reckoning was the primary method of determining longitude available to mariners such as Christopher Columbus and John Cabot on their trans-Atlantic voyages. Tools such as the traverse board were developed to enable even illiterate crew members to collect the data needed for dead reckoning. Polynesian navigation, however, uses different wayfinding techniques.
caption: Dead reckoning navigation tools in coastal navigation
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