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Navigation and location of the ship by geopositioning techniques based on the observation of the stars and other celestial bodies. The variables measured to find the location are: the observed angular height of the stars above the horizon , measured with the sextant (formerly with the astrolabe or other instrument), and the time , measured with ...
Aboard ship a dead reckoning plot is considered important in evaluating position information and planning the movement of the vessel. [8] 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.
The system works by triangulating the ship's position based on directional reference to known transmitters. Global Positioning System (GPS) : GPS was designed by the US military with the primary purpose of addressing "drift" within the inertial navigation of Submarine-launched ballistic missile (SLBMs) prior to launch.
Inertial systems are devices that measure a vessel position over time with motion sensors and gyroscopes. These devices estimate future positions based off velocity, acceleration, and orientation measurements. Detected anomalies that stray from the expected pattern can be flagged for closer inspection.
When a vessel (ship or boat) is within radar range of land or fixed objects (such as special radar aids to navigation and navigation marks) the navigator can take distances and angular bearings to charted objects and use these to establish arcs of position and lines of position on a chart. [32]
In his notes on Ptolemy's geography, Johannes Werner of Nuremberg wrote in 1514 that the cross-staff was a very ancient instrument, but was only beginning to be used on ships. [36] Prior to 1577, no method of judging the ship's speed was mentioned that was more advanced than observing the size of the vessel's bow wave or the passage of sea foam ...
The longitude rewards were the system of inducement prizes offered by the British government for a simple and practical method for the precise determination of a ship's longitude at sea. The prizes, established through an act of Parliament, the Longitude Act 1714 (13 Ann. c. 14), in 1714, were administered by the Board of Longitude.
The intersection of these lines is the current position of the vessel. Usually, a fix is where two or more position lines intersect at any given time. If three position lines can be obtained, the resulting "cocked hat", where the three lines do not intersect at the same point, but create a triangle, gives the navigator an indication of the ...