Marine Electronics - GPS, LORAN-C, Fish Finders, VHF Marine Radios
GPS receivers are one of the most popular electronic devices today. Equipment ranges from simple hand held units to programs driven by modules which attach to a PC.
Popular GPS features include waypoint lists, plotter, routes and upload/download functions. The waypoint list gives users the ability to keep track of the numerous waypoints that are saved while fishing. Plotters are used to see a user's position in relation to other waypoints.
The most revolutionary feature of the present day GPS units is their ability to upload and download data. This feature allows users to edit recent waypoints, upload files from other sources, and create backup files.
Coupled with the appropriate software, a mariner can manage waypoint lists, view waypoints overlaid onto digital charts and much more. Software for this feature is abundant but may be limited to specific GPS models. Some GPS units can also receive software updates right from the internet using the upload feature.
Disadvantages of portable GPS units include their lack of an external antenna, need for batteries, and small screen.
LORAN - C
LORAN was the first type of electronic navigation for many fishermen. It revolutionized fishing in a variety of ways. Prior to LORAN-C, most fishermen used a chart, ruler, and compass to navigate. Basic navigation was time consuming, distracting and sometimes dangerous.
When most people mention LORAN, they refer to LORAN C which is a refinement of earlier LORAN systems. LORAN C is widely misunderstood and does have it's peculiarities. The basic concept uses a radio receiver to determine a vessel's position by determining the time delays or TD's of an array (typically 2) of LORAN stations. The pair of numbers displayed on a LORAN equates to a certain geographic position. The exact value can be affected by several factors but the repeatability of a fix obtained by LORAN was excellent. Charts were overlaid with lines of position (LOP) for W, X, Y and Z stations. The predicted lines are very accurate over open water but cannot be predicted over land.
Converting LORAN-C TD's to geographic coordinates is upon several factors including the position, LORAN model from which the TD's originated, and other factors. Conversions of a batch of numbers within a limited area can be done using a computer program from Andren Software called "LORANGPS". Basically a fix needs to be taken for a test spot within the conversion file area with both the LORAN and a GPS. Additional secondary factors or ASF's can then be adjusted in the chosen program until the LORAN and GPS positions match. Once a value for ASF's is attained, it can be applied to all positions within the local area. The result is a group of old LORAN data which can now be used with a GPS.
VHF Marine Radios
VHF marine radios are essential equipment on most fishing boats. The usable range of a VHF radio system is dependant on several factors including weather, the type and placement of the antenna, and other factors. The most important part of the system is the antenna. Marine antennas should be mounted as high as practical. Another important quality of an antenna is it's gain.
Gain is rated in decibels (dB). Most experts recommend a quality antenna with 6 a gain of dB for powerboats under 50 ft. The antenna system can be tested by measuring the VSWR of the antenna. In most cases, VSWR should be not more than 1.5 to 1.
Other radio problems can stem from the radio or the vessel electrical system. One of the most frequent radio system failures on fishing boats occurs a poor connection exists between the radio and battery. The radio will normally come on but may transmit erratically or not at all. If other accessories are on the same circuit, keying the radio transmitter will likely affect those units as well.
Receivers, including VHF marine radios, GPS units, and other devices can all suffer from interference on a boat. Interference usually originates from other sources in the boat electrical system. One common example is "clicking" or "pinging" heard in the radio when a fish finder is on. This and other symptoms can be minimized by running the proper sized electrical power wiring for each device all the way to the battery switch. In some cases electrical filters will need to be installed to combat interference.
Two acronyms that boaters may want to learn about are Digital Selective Calling (DSC) and the Global Maritime Distress and Safety System (GMDSS). DSC is secure digital format which allows users to communicate with other DSC equipped radios. In a nutshell GMDSS is a system that allows a radio to send an automated distress call which can include vessel position information IF the radio is connected to a working GPS unit.
Fittings and Adaptors
There are several types of connectors found on marine electronics. UHF fittings are the most common, normally on VHF radios. Another common type is BNC which will often be used on LORAN or GPS antennas. Other types are mini-UHF, N, SMA and TNC.
The connectors pictured are from left to right:
TNC, BNC, UHF, MINI-UHF, N, SMA