GPS Chartplotters

May 12, 2015
By Bill Jennings
originally posted March 1, 2012.
Helping you get where you want to go.

Most of us have used a GPS – a Global Positioning System.  If not in our boat, we have one in our car. Did you know that the inspiration and development for GPS dates back to WWII. In 1960, the first navigation system utilizing satellites had the ability to interface with five satellites and provided a ‘fix’ about once per hour. Obtaining US government approval for the billions necessary for further development of the system can be credited to the ‘cold war’. At that time a superior system was needed by the Navy for its submarine missiles, the Air Force for its bombers, and the army for ICBMs.

The updated system for the GPS we know today began with the launch of satellite one in 1989 and the twenty fourth satellite in 1994. Average orbital altitude for these satellites is 12,547 miles and their average velocity is 4,666 mph, which takes them twice around the earth each day. Initially, the highest quality signal was reserved for military use, but in the year 2000, “selective availability” as it was referred to, was turned off, improving the accuracy for civilian-use from about 300 feet down to just 65 feet.  (That’s still too much room for error to rely solely on your GPS for navigation.)  None-the-less, the US government controls the export of GPS units that are capable of operating above eleven miles or a speed of 1,001 Knots per hour. These are classified as ‘munitions’ and as such, require State Department licenses. There are few other restrictions on GPS units for civilian use.

With GPS satellites providing the exact longitude/latitude for your position, it was a relatively simple process to match this information up to the longitude/latitude on marine charts, thereby creating today’s electronic chartplotters. A multitude of electronic manufacturers offer a selection of GPS chartplotters. When you buy be sure to check the date on the charts used in your unit and that the screen is large enough and bright enough for your application.

So how good is a GPS unit for marine navigation? It’s excellent!  I recently discussed navigating and electronics with a senior navigational officer working for a major cruise line. He confided in me that prior to a cruise he looks up online the current electronic British American charts. BA charts are approved for commercial use and are updated every week. He then downloads these charts from the Internet into his $700 iPad and carries it onboard with his personal gear. On the bridge, he uses a suction cup to attach the iPad to the front windscreen and proceeds to use this as his primary navigational reference.  He notes that inertia systems and celestial navigation are good to have available, but in practice today they are seldom used. Such iPad usage for navigation extends to aviation, where pilots download detailed airport information, approach plates and charts then refer to an iPad for both VFR and IFR flights.  Such applications indicate we may soon see carry on tablets replacing the more bulky fixed units found in
today’s boats.

What boaters need to remember is that while GPS gives you a good idea of where you are relative to buoys and shorelines shown on a chart, it does not tell you anything about the on-water boat traffic around you; nor does it account for outdated nautical charts. For this information we must rely on our eyes and/or the radar system – if your boat is so equipped. Another point to remember is that buying a current GPS system can be very different than installing it in your boat.  Installation can be tricky. If you are handy with electronics you shouldn‘t have a problem, but if you are like me, there is always some little thing that takes forever to figure out. So to be on the safe side, budget an extra cost for professional installation assistance.

In addition to the US system, there are other GPS systems now available, or under development. The Russian GLONASS was made fully available to citizens in 2007. As well, the European “Galileo”, the Indian “RNSS” and the Chinese “CNS” are soon to be released. So in addition to being a simple and accurate satellite navigation aid, it seems that GPS systems will be available to boaters for many years to come. And there is no doubt that GPS gives the weekend boater the ability to navigate in a variety of weather conditions with much improved confidence and safety.