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Estimating a position by plotting a record of courses run and distances sailed.

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Twin rulers hinges side by side that can be used to walk from one line on a chart to another that is parallel. Used for plotting a position or a course line on a chart


  1. Charts are constructed on many different scales, ranging from about 1:2,500 to 1:14,000,000 (and even smaller for some world charts). Small-scale charts are used for voyage planning and offshore navigation. Charts of larger scale are used as the vessel approaches land. Several methods of classifying charts according to scale are in use in various nations. The follow- ing classifications of nautical charts are those used by the National Ocean Survey: Sailing charts are the smallest scale charts used for planning, fixing position at sea, and for plotting while proceeding on a long voyage. The scale is generally smaller than 1:600,000. The shoreline and topography are generalized and only offshore soundings, the principal navigational lights, outer buoys, and land- marks visible at considerable distances are shown. General charts are intended for coastwise navigation outside of outlying reefs and shoals. The scales range from about 1:150,000 to 1:600,000. Coast (coastal) charts are intended for inshore coastwise navigation where the course may lie inside outlying reefs and shoals, for entering or leaving bays and harbors of considerable width, and for navigating large inland waterways. The scales range from about 1:50,000 to 1:150,000. Harbor charts are intended for navigation and anchorage in harbors and small waterways. The scale is generally larger than 1:50,000. 2. The classification system used by the National Imagery and Mapping Agency differs from the system in definition 1 above in that the sailing charts are incorporated in the general charts classification (smaller than about 1:150,000); those coast charts especially useful for approaching more confined waters (bays, harbors) are classified as approach charts.


A device for projecting a set of precomputed altitude curves onto a chart or plotting sheet, the curves moving with time such that if they are properly adjusted, they will remain in the correct position on the chart or plotting sheet.


For a relatively small area, a good approximation of a Mercator position plotting sheet, constructed by the navi- gator by either of two methods based upon graphical solution of the secant of the latitude which approximates the expansion. A partially completed small area plotting sheet printed in advance for later rapid completion according to requirements is called UNIVERSAL PLOTTING SHEET.


Mooring lines which run from forward to an after position on the dock and aft to a forward position on the dock. These lines prevent forward and aft movement when a vessel is moored.


The most probable position of a craft determined from incomplete data or data of questionable accuracy. Such a position might be determined by applying a correction to the dead reckoning position, as for estimated current; by plotting a line of soundings; or by plotting lines of position of questionable accuracy. If no better information is available, a dead reckoning position is an estimated position, but the expression estimated position is not customarily used in this case. The distinction between an estimated position and a fix or running fix is a matter of judgment.


In the operation of automated radar plotting aids, the process of observing the sequential changes in the position of a target to establish its motion.


A line of position which has been moved forward along the course line to allow for the run since the line was established. The opposite is RETIRED LINE OF POSITION.


An object which has rest-mass and an observable position in space, but has no geometrical extension, being confined to a single point. Also known as particle.


A system which uses a standard-scaled grid square, based on a point of origin on a map projection of the earth’s surface in an accurate and consistent manner to permit either position referencing or the computation of direction and distance between grid positions.

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