Chuck Husick: Techno-Talk, March 2005 from BoatUS Magazine - Updated December 2008
are among today's most popular electronic navigation aids. The course
plotters built into many GPS receivers are the most basic. While presenting
no cartography data they plot the vessel’s course over the ground
to the accuracy of the GPS signal and are invaluable in preserving a
record of the path the boat traveled, making it easy to retrace one’s
course in an uncharted anchorage. Many boaters will find that a GPS
plotter and a good depth sounder should satisfy most of their electronic
Integrating cartography with the GPS position information creates a
true chart plotter rather then a simple course plotter. Systems in between
the course plotter and the chart plotter fall into two broad categories,
special purpose hardware using a fixed operating program and those that
operate on personal computers running a proprietary software program.
The way you intend to use the system should guide your choice.
Chart plotters used as real-time navigation aids should be located in
easy view of the helm and have display screens bright and clear enough
to be seen without excessively distracting the helmsman. These systems
work best when equipped with dedicated controls (either hardware buttons
or keys or “soft” keys) that provide direct access to the
desired data display, without the need to progress through menu choices
to access the needed data.
Regardless of screen size, the system should allow de-cluttering of
the display to enhance visibility of critical navigation information.
Most of the plotters that meet these criteria are dedicated hardware
/ software devices. Many of these units combine a number of display
functions; cartography, depth sounder / fish finder, radar, closed-circuit
TV monitor and weather data, either from a satellite link or from a
weatherfax receiver. It is increasingly common to refer to chartplotters by a more accurate name, Muti-Function-Displays (MFDs) since the navigation chart is only one of the types of navigation and vessel status information they present to the navigator.
In addition to real-time navigation, chart plotters are also used to
create voyage plans and to capture a detailed record of a vessel’s
operation, including the information needed to create “polars”
for a sailboat and cruise efficiency curves for a powerboat. In such
applications, the plotter may be located at a boat’s chart table,
a location amenable to laptop computer use. The navigation software
programs used usually run under Windows on a PC, however an outstanding
program that runs on the latest Macintoshes (www.GPSNavX.com) offers two chartplotter programs, GPSNavX and MacENC, the latter capable of superimposing the familiar raster navigation chart (RNC) on an electronic navigation chart (ENC) to provide the navigator with instant access to the entire chart database. The latest version of MaxSea, which runs under Windows offers TimeZero access to charts, eliminating the normal time-out other systems require for screen re-draw. This system is also a part of the Furuno NavNet3D system that has set a new standard for top of the line multi-function displays. These programs usually provide a broad range of capabilities,
including an interface with the boat’s wind velocity, heading
and hull speed sensors and the ability to capture and store a virtually
unlimited volume of data. However, the user interface of some software
programs may be significantly less user friendly than the dedicated
The most critical element in a chart plotter is the display screen.
Although large screens are just as attractive in a plotter as they are
in a TV set, you don’t have to have a big screen to make the data
you need visible. Placing a small screen unit close at hand will make
it easy both to manipulate the controls and to see the information on
the screen. Units with screens no larger than some PDAs can perform
very well. A number of applications for the Apple iPhone, including iNavX can provide fully functional chartplotter operation, including downloading any US RNC and integrating tide and current information. In addition, when in range of a wifi signal or a cell phone tower the iPhone can access real time images of National Weather Service Doppler radar and all other NWS products. Regardless of display screen size, the unit you choose must
be able to withstand exposure to its environment. Unless it is below
deck, waterproof is the way to go, something that may be a challenge
with a laptop computer.
Regardless of your choice of chart plotter remember that a prudent helmsman
never relies exclusively on a single source of navigation data. The
chart you see on the screen may be slightly or, in some cases, grossly
incorrect. Always use all available information, including paper charts.
Following the previously recorded plot of your successful course into
that delightful anchorage may get you in trouble if you fail to take
the height of the tide into account or if a storm has moved the sand
Putting too much data on the screen at one time can create undesirable
confusion. Viewing radar data overlaid on the chart can create problems
if the boat’s heading sensor is inaccurate or lags behind in heading
Often the simplest picture is the best choice.