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Shopping Advice for Multifunction Display Chartplotters and Navigational Units


GPS Navigation Electronics and Software

chartplotter navigational display

Navigating the Multi-Function Choices

Selecting navigation electronics can be a bit overwhelming with all of the multifunction units out there. This overview should help you select the best fit for your needs.

If one unit is capable of so many things, by which name should you call it? In general, fish finders will offer the user a fair to very high resolution picture of the bottom, whereas a sonar simply reports a number for the depth. Add GPS to the mix, and the piece of electronics will report exact coordinates of your present location. Most GPS units on the market today combine the position fixing with a chartplotting software. This records your track, speed, distance and puts your fix into the context of a nautical chart or land map. Radar is a further integration capability in many high end navigation systems. This typically does not mean all features are included in the box. If a unit is called a "fishfinder" and you also desire chartplotting, be sure it is included in the package or look into the cost to buy the required navigation software separately. Some units come pre-loaded with all charts of North America out of the box. GPS electronics may also require a separate antenna. You need the antenna if not built in already or if you are mounting the GPS inside cabin space. If the suite of fishfinding and navigation software is included, many manufacturers will call it a fishing or navigation "system." Radar is nearly always a separate add on. It requires purchasing at minimum an array, either open array or radome. It may also require a switch box of sorts to manage network feeds from transducers, arrays, etc. Most major brand navigation electronics offer units that can do all these functions from the commands of one display. Be sure to investigate what is included in each box and evaluate the entire parts purchase when shopping. To integrate all of these functions into one display there is typically a link or hub which will speak to the monitor. The signal needs to be the same network language for all electronics concerned, either NMEA 2000 or older NMEA 0183 feed. (National Marine Electronics Association) With the common feed, a single display becomes a capable depth finder, nautical chart plotter, navigation instruments, engines, tank level sensors, and GPS receiver, even trim tab controller. If you intend to incorporate all these systems into one unit, a word of advice is to select a screen large enough. It is difficult to monitor all these at once unless the screen can provide quality resolution during split screen views.

So What is this NMEA thing?

NMEA stands for National Marine Electronics Association. To be certified NMEA 0183 or NMEA 2000 compatible devices go through a rigorous certification process overseen by the NMEA, and are permitted to display the "NMEA 2000 Certified" logo once they have completed the certification process. The certification process does not guarantee data content, that is the responsibility of the manufacturers. However, the certification process does assure that products from different manufacturers assemble and exchange data in a compatible way and that they can coexist on a network. The term "NMEA 2000" is a registered trademark of the National Marine Electronics Association. Devices which are not "NMEA 2000 Certified" may not legally use the NMEA 2000 trademark in their advertising.

Electronic Compass

A basic necessity on any boat, a magnetic compass is irreplaceable. Since at it's core it works as a magnet, it will function without power. An electronic compass is a great addition for improved accuracy. It is correctable for deviation. Electronic compasses will also provide required information to autopilots, radar displays and chart plotters. The magnetic heading information is detected through a magnetic flux gate. This is essentially four coils of thin wire wrapped around an easily magnetized metal core. AC voltage is introduced to one coil. The relative voltage strength induced in the three remaining coils depends upon alignment with Earth's magnetic core. Thus sensing the induced voltage will indicate vessel heading. For accuracy, a flux gate compass needs to be parallel to the earth's surface. It is therefore suspended in a housing like other style compasses, and usually filled with light oil. Instead of manual adjustment to a conventional compass, flux detector compasses self correct easily by pressing a button and turning the boat through the points of the compass for few minutes. They offer improved accuracy on most headings but still are prone to the same errors of a conventional compass in extreme northerly and southerly latitudes. They will also tend to lag behind in rapid accelerations or turns like a traditional compass. Rate of turn gyros are added in many modern autopilots to compensate for these momentary errors.



-Michael Reardon

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