Glossary of Marine Electronics

Posted on August 25, 2010, 8:53 pm

Autopilots The first self-steering ratio has been set up in 1920 to control model yachts but it was not until 1948 that the principle has been applied to large scale yachts. Standing at the bar for long periods, monitoring instruments and keeping a good look, can be very tiring. An autopilot relieves the helmsman to steer the correct course leaving him free to maintain a proper lookout. The autopilot can be set to either steer a compass course or a course by the wind. A fluxgate compass or electronic vane feeds information to a microprocessor which then makes the necessary rudder movements to return the vessel to its required courses. The mechanical power is applied to the rudder by either electric linear activators, hydraulic pumps or rotary discs. GPS / card readers can be used to input navigation instructions to the autopilot. Battery Chargers will keep batteries fully charged thereby extending their working life. Chart Plotters Typically, a card reader comprises an antenna, mounted high on the boat, to track GPS signals and a display unit located either at the navigation station or the helm of ship. The boat position is sent from the antenna to the display unit, which in turn, shows graphically on the map. The table itself looks like its paper equivalent and show depth, land mass, navigational aids such as buoys and hazards in the form of wrecks and obstructions. The user can add waypoints to the map and zoom in and out of the screen. Card readers can be connected to drive an autopilot and / or send data to a GPS fish finder or radar. They can also interface with a laptop enabling complex passage planning to be away from the boat, then walked into the card reader after his arrival at the boat. Transmission Magnetic Compass work like traditional compasses using magnets to determine the direction of the magnetic field of ships land which they then send the boats to the electronic display. They are steering easier than conventional compasses because they display more stable position and do not suffer from “lag” that occurs during a turn. They can interface with card readers, autopilots and radar. Fluxgate compass composed of two pieces of magnetic material easily saturated with coils wound round them in opposite directions. The alternating current is passed through the coils and the material is saturated in one direction and then another. The Earth’s magnetic field affects slightly when the saturation occurs earlier in a coil, then the other. The difference is then calculated by taking an output proportional to the magnetic field of the earth. They are accurate to 0. 1 degree. Their output can be displayed digitally to the helmsman or they can interface with autopilots and radar card readers. Sounders work on the same principle as sonar. A transducer emits a narrow beam of high frequency sound. This is reflected by solid objects and the delay between transmission and reception of the echo is measured. The speed of sound in water is known and if the range or distance from the bottom of the sea can be calculated. Which is then displayed in meters. Forward Looking Sonar (FLS) enables you to see the underwater dangers before you actually above them. A typical range of FLS is 150 meters. An Emergency Position Indicating Radio Beacon (EPIRB) is a piece of equipment designed to float free of a ship in distress. It then sends a radio signal that can be detected by the search and rescue satellite Computer Aided Tracking (SARSAT) satellites. They send a message to a ground station which in turn may initiate a search operation and rescue. Fish finders use the same technology as sonar. A narrow beam of high frequency sound is transmitted by a sensor, which is reflected by solid objects such as the seabed. By developing this technology displays provide pollsters show where fish are and they can not differentiate between baitfish and larger speciesGlobal Positioning System (GPS Receivers) – This system was originally designed for military use and is owned and operated by the U.S. Department of Defense. 24 satellites are arranged in a bird cage “around the world, they are positioned so that anywhere on the surface of the earth line of sight can be set at a minimum of 4 satellites. A patch is obtained by accurately measuring the distance between a satellite and GPS receiver at a particular time. Because the exact position of the satellite is known, these distances provide position lines which are converted by a microprocessor in the GPS receiver to read outs of latitude and longitude. The log is used to measure the speed of boats in the water. A paddle wheel or impeller, mounted below the waterline is turned by water flow, which generates electrical impulses that are transmitted to a microprocessor that displays speed and distance traveled. Inverters – On most boats today you will find domestic equipment of one kind or another. For entertainment there are televisions on board and stereos. With the popularity of card readers is the PC or laptop. Maintenance often requires the use of power tools. Cruise could have a washing machine, dishwasher or microwave. May take 12V 24V or 48V supply and convert it into a stable 110 V or 220 V AC. Navtex can perhaps best be described as a telex service provides continually updated navigation and weather information within specified areas. A board on the receiver, tuned to 518kHz, frequency Navtex worldwide, if left turned on will either print or display the latest massages sent from a local station. The service is available up to 400 miles offshore . Radar lets you see what otherwise would be invisible. They offer more advantages in the night and in fog or rain and are of particular value when close to the coast or sea routes. They are made of an antenna and a screen. The antenna sends a stream of RF energy which is reflected by hard objects. When this energy is returned, it is converted into a signal that appears to the user. The antenna rotates every few seconds, the display continuously calculates the direction of the antenna and so a precise impact of the target is calculated. The time is measured by the energy to be taken into account and if the distance of the target is also displayed . Satellite phones consisting of an antenna, a modem and a regular phone. They are powered by a battery of iridium. Their range is anywhere covered by the Inmarsat Mini-M satellite. Voice, fax, email and data can be transmitted. satellite TV requires an antenna and of course television. The reception is available in a “fingerprint” that is based on EIRP (equivalent isotropic radiated power) of a satellite transmission. EUTELSAT satellites with ASTRA two cover Europe. Nilesat and Arabsat cover both Africa and the Middle East. Good coverage is also available in North America, Central and South America. SSB Radio has a range of several thousand miles. You need an FFC license, or equivalent in any country you plan to run it. Energy consumption is a consideration. Up to 100 Watts may be necessary for transmission. SSB radio requires several pieces of equipment. A transceiver capable of operating SSB, an antenna, it must be 8 meters long and in practice most boats use a backstay or shroud for the purpose of equipping the necessary insulation. A antenna tuner, the model transceiver. If you want to send an email, and you will also have a radio modem and computer. VHF power needed to transmit is minimal, every game has the possibility of transmission each 1 Watt or 25 Watts and less energy should be used whenever possible. Unlike phones that can both speak and listen at the same time most VHF sets require you to press a button issue before speaking. This is called simplex. Duplex sets are available but are much more expensive. VHF radio waves travel in straight lines, so the antenna must be mounted as high as possible, preferably masthead.