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Understanding the GPSThe GPS system is based on a network of 24 satellites which orbit around the world at an altitude of 20 178 km (base orbit.) These satellites emit information on their position and the exact hour (atomic clock)… This information is received by the GPS receiver and permits it to calculateposition. On a GPS receiver everything is automatic, it captures signals from the satellites it surveys and works out its position. In order to do this from a position without altitude, it must receive signals from at least 3 satellites. The more satellites viewed, the more accurate the position. Fixed or portable, regardless of brand or price, all GPS receivers work with the same satellites and display the same position, within a precision of the order of tens of metres f
Choosing your cartographyBefore selecting a card reader, it is necessary to choose its cartography. Each device operates with a unique brand chart. You can explore the characteristics of each of three brands of charts available today in our, “cartography,” dossier. Note that with the exception of Garmin, which has cartography useable only on its own brand’s devices, Navionics and C-Map charts may be read by different brands of readers. There i though, no universal reader. A reader designed to read Navionics charts cannot read C-Map charts and vice versa.
RegulationsSince the 1st January 2010, the presence of paper charts on board is no longer obligatory, provided they are replaced by electronic versions. This measure was dictated by the fact that more and more pleasure sailors are travelling with electronic charts. Still, no one is safe from electrical problems on board. All responsible sailors should take paper charts too, in case of emergencies.
Raster or vector mapping?To make electronic charts there is a choice between two methods: scanning
How does it work?All sounders, graphic or not, function on the same principle. A transmitter/receiver (sensor,) located under the boat sends a sonar signal vertically toward the bottom. When this signal encounters an obstacle, itis returned to the sensor. The sensor’s clock calculates the time taken (transmission/reception) and calculates the depth. This is then displayed, digitally or graphically.
Selection criteria-The number of vertical pixels
Whether monochrome or colour, the screen must be very fine to displaythe details. This i
How does radar function?The signal emitted by the antenna is reflected when it encounters an object and returned to its starting point. This principle may be compared with that of sonar. Radome or apparent, the antenna rotates at about 24 rev/min covering 360°around the boat. To minimize energy consumption, the signal (from 2 to 6 kW, depending on the model,) is sent as short pulses and for optimizing the range as a narrow beam (5 ° in the horizontal plane and 25 ° vertically. ) In normal use the boat is at the centre of the screen, boat’s heading at the top. To measure the bearing and distance of a target relative to the boat, we use the VRM (variable range) and EBL (alidade mobile.) It positions the VRM circle and the EBL on the target (boat, coast, rock…) The VRM indicates precisely the di