To maximize your investment and minimize down time, every boater should take a little time and get to know your marine GPS.  GPS (Global Positioning System) has made precise navigation a breeze for everyone from the wilderness hiker to the offshore boater.  They’re small, relatively inexpensive, and generally easy to operate.  However, knowing the basics on just how the system works and a few particulars about the unit you’re using is a good idea. 

     Automation is nice but can lull us into a false sense of security.  Granted, today’s GPS units and the system itself are very reliable and perform flawlessly most of the time.  However, given enough time, things can and will go wrong.  That’s when just a little knowledge could come in handy and go long way toward helping you understand why your GPS isn’t doing its thing.

     The first thing you should keep in mind is that your GPS unit receives its information directly from satellites.  Therefore, having an unobstructed view of the sky is critical.  Not all of the sky, but a significant portion of it.  Fortunately there are multiple GPS satellites and it only takes 2 or 3 of them for you to get an accurate and reliable fix. 

     Almost all GPS units have a way of monitoring the number of satellites it can see and measuring the strength of the signal from each one.  You should make sure you know how do find this function in your particular GPS receiver.  You shouldn’t be concerned about which satellites you’re receiving, just how many and their signal strength.  That information is normally presented in a standard bar graph display.  Some units also show a circular pattern with the position and ID number of the satellites currently in view.  The figure below is typical of what you may see.

     It’s a good idea to know at a glance whether the satellite data display indicates a problem or not.  Reading your owners manual is always a good idea but you can also simply establish a benchmark that will tell you at a glance if something is obviously different than it usually is.  When things are working normal, check the satellite display and notice what it looks like.  Make note of the number of satellites and the average signal strength levels.  If you have a portable GPS, move to different locations and watch what happens to the signal strength.  Know just how much blockage your unit will tolerate until it looses enough signal to no longer lock on.

     Boaters should be aware that external interference can negatively effect the performance of the your GPS.  You should set your benchmark with everything else on the boat turned off.  Turn things on one at a time while watching the satellite signal strength display.  Particularly watch when you start your engines and turn on pumps and motors.  Even TV’s, especially with amplifiers on the antenna, can cause a reduction or even complete loss of satellite signals.  If you find that to be the case, the problem may be cleared up or at least improved by grounding the TV antenna cable.  However, simply turning the TV and/or amplifier off usually restores normal operation to your GPS.         

     Familiarizing yourself with your GPS unit as well as the other marine electronics on your boat will better prepare you to deal with those unexpected malfunctions and glitches that inevitably show up at the worse possible times.  For more information on this and other things a boater should know about marine electronics, visit Marine Tools & Info and Technical Articles in the Marine Support section at www.NavShack.com.

Dave has spent almost 40 years in the marine electronics industry as a technician, manager, and business owner. He earned a 1st Class FCC Radiotelephone License with Ship Radar Endorsement in 1972 and has received numerous accreditations from
manufacturers, and trade associations.

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