Search results
Results from the WOW.Com Content Network
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.
A diagram of a typical nautical sextant, a tool used in celestial navigation to measure the angle between two objects viewed by means of its optical sight. Celestial navigation, also known as astronavigation, is the practice of position fixing using stars and other celestial bodies that enables a navigator to accurately determine their actual current physical position in space or on the ...
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 ...
The fourth and final stage of voyage planning is the monitoring stage. Once the voyage has begun the progress of the vessel along its planned route must be monitored. This requires that the ship's position be determined, using standard methods including dead reckoning, celestial navigation, pilotage, and electronic navigation.
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]
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.
A marine chronometer is a precision timepiece that is carried on a ship and employed in the determination of the ship's position by celestial navigation.It is used to determine longitude by comparing Greenwich Mean Time (GMT), and the time at the current location found from observations of celestial bodies.
In order to calculate the position line, the time of the sight must be known so that the celestial position i.e. the Greenwich Hour Angle (Celestial Longitude - measured in a westerly direction from Greenwich) and Declination (Celestial Latitude - measured north or south of the equational or celestial equator), of the observed celestial body is ...