Chuck Husick: Techno-Talk, March 2005 from BoatUS Magazine -

Chartplotters

Chart plotters 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 navigation needs.

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.

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) was introduced recently. 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 hardware systems.

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. 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 about.

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 changes.

Often the simplest picture is the best choice.